EP3591081B1 - Method for producing a case-hardened steel component - Google Patents
Method for producing a case-hardened steel component Download PDFInfo
- Publication number
- EP3591081B1 EP3591081B1 EP18182024.2A EP18182024A EP3591081B1 EP 3591081 B1 EP3591081 B1 EP 3591081B1 EP 18182024 A EP18182024 A EP 18182024A EP 3591081 B1 EP3591081 B1 EP 3591081B1
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- European Patent Office
- Prior art keywords
- steel
- steel component
- weight
- temperature
- hardening
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- 238000004519 manufacturing process Methods 0.000 title claims description 17
- 229910000760 Hardened steel Inorganic materials 0.000 title claims description 6
- 229910000831 Steel Inorganic materials 0.000 claims description 153
- 239000010959 steel Substances 0.000 claims description 153
- 229910052757 nitrogen Inorganic materials 0.000 claims description 25
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 22
- 229910052758 niobium Inorganic materials 0.000 claims description 21
- 229910052719 titanium Inorganic materials 0.000 claims description 21
- 229910052720 vanadium Inorganic materials 0.000 claims description 21
- 229910001563 bainite Inorganic materials 0.000 claims description 20
- 229910052799 carbon Inorganic materials 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 19
- 229910052782 aluminium Inorganic materials 0.000 claims description 17
- 238000001816 cooling Methods 0.000 claims description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 12
- 229910052796 boron Inorganic materials 0.000 claims description 9
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 9
- 229910052750 molybdenum Inorganic materials 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 8
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- 229910000734 martensite Inorganic materials 0.000 claims description 7
- 229910052710 silicon Inorganic materials 0.000 claims description 7
- 229910052717 sulfur Inorganic materials 0.000 claims description 7
- 229910000859 α-Fe Inorganic materials 0.000 claims description 7
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 238000005496 tempering Methods 0.000 claims description 5
- 229910001566 austenite Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 235000019362 perlite Nutrition 0.000 claims 1
- 239000010451 perlite Substances 0.000 claims 1
- 239000010955 niobium Substances 0.000 description 22
- 239000002344 surface layer Substances 0.000 description 22
- 239000010936 titanium Substances 0.000 description 22
- 238000005255 carburizing Methods 0.000 description 21
- 230000015572 biosynthetic process Effects 0.000 description 16
- 238000009792 diffusion process Methods 0.000 description 15
- 239000011651 chromium Substances 0.000 description 14
- 239000011572 manganese Substances 0.000 description 13
- 230000000694 effects Effects 0.000 description 12
- 238000005121 nitriding Methods 0.000 description 11
- 239000010410 layer Substances 0.000 description 10
- 229910045601 alloy Inorganic materials 0.000 description 9
- 239000000956 alloy Substances 0.000 description 9
- 238000005256 carbonitriding Methods 0.000 description 9
- 230000009466 transformation Effects 0.000 description 9
- 230000008569 process Effects 0.000 description 8
- 239000011159 matrix material Substances 0.000 description 6
- 238000005275 alloying Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910001562 pearlite Inorganic materials 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 4
- 238000003754 machining Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 3
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000005242 forging Methods 0.000 description 3
- 239000011733 molybdenum Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 239000003921 oil Substances 0.000 description 2
- 238000004663 powder metallurgy Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- -1 chromium nitrides Chemical class 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 230000001131 transforming effect Effects 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/28—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for plain shafts
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/06—Surface hardening
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/32—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for gear wheels, worm wheels, or the like
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/02—Pretreatment of the material to be coated
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
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- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/20—Carburising
- C23C8/22—Carburising of ferrous surfaces
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
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- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/24—Nitriding
- C23C8/26—Nitriding of ferrous surfaces
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/28—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in one step
- C23C8/30—Carbo-nitriding
- C23C8/32—Carbo-nitriding of ferrous surfaces
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/34—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in more than one step
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/80—After-treatment
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2221/00—Treating localised areas of an article
- C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
Definitions
- the invention relates to a method for producing a case-hardened steel component. If "%" information is given below about alloys or steel compositions, these relate to weight, unless expressly stated otherwise.
- the steel components considered here are typically components that in practice come into metallic contact with other components in a rolling or rolling movement and are therefore exposed to high mechanical loads in the area of their contact surface.
- Typical examples of such components are gears, shafts or axles. Comparable loads can occur in the case of tool holders, for example cutting tools and the like, come in the area of the contact surfaces between the holder and the respective tool.
- case hardening steels are typically used today for gear manufacturing, examples of which are the steels with 16MnCr5 / 16MnCrS5 (material numbers 1.7131 /1.7139) and 18CrNiMo7-6 (material number 1.6587).
- Tool holders such as holders for cutting bodies produced by powder metallurgy, are often made from relatively expensive tool steels, such as steels with the material numbers 1.2311, 1.2312, 1.2738, 1.2343 or 1.2343.
- Case hardening in which the surface layer of the steel component is first subjected to a carburizing or carbonitriding treatment to increase the carbon content, is one of the common methods with which gearwheels and components that are subjected to comparable loads in use can be provided with a hardened surface layer and then the component undergoes hardening in order to achieve maximum hardness in the hardened surface layer, and nitriding or nitrocarburizing (see leaflet 477), in which the increase in hardness of the surface layer is essentially achieved by diffused nitrogen, with an additional increase in hardness by can be achieved in combination with the nitrogen diffused carbon.
- the object of the invention was to name a method for producing a steel component which has the optimum combination of properties in those surface-hardened by a thermochemical diffusion treatment Steel components that are in rolling or rolling contact with another component during use.
- a surface-hardened steel component is also disclosed, which has an optimal combination of hardness in its surface layer and toughness in its core area bearing the surface layer with regard to its fatigue strength.
- the invention includes the method according to claim 1.
- the steel to be used according to the invention opens up a robust and cost-effective production route for the production of steel components to be surface hardened by a thermochemical diffusion treatment, namely gear wheels, axles, shafts or tool holders with special application conditions.
- a thermochemical diffusion treatment namely gear wheels, axles, shafts or tool holders with special application conditions.
- the components produced from steel used according to the invention have a higher toughness in their core area, also called “matrix", than is the case with steels commonly used for this purpose today.
- the invention is based on the knowledge that a modification of a steel forming a bainitic structure, which is basically from the publication EP 3 168 312 A1 a European patent application is already known for the forging production of components, is also particularly suitable as a material for the production of steel components with a thermochemically hardened surface layer. It has surprisingly been shown that the alloy concept intended for forging applications also has considerable advantages in terms of the toughness of the steel component in its core area due to the high tempering resistance of the bainitic structure of the steel proposed for use according to the invention.
- the steel known per se from the publication of the aforementioned European patent application, as in FIG EP 3 168 312 A1 explained in detail, has a wide bainite window in the time-temperature diagram ("ZTU diagram"), i.e. reliably forms a bainitic structure dominated by bainite to at least 80% by volume over a large range of cooling speeds.
- ZTU diagram time-temperature diagram
- the known alloy specification ensures these properties of the steel even if the steel is not cooled from the forging heat, as originally intended, but is subjected to a thermochemical diffusion treatment. This also applies if the respective steel component is subjected to hardening after the diffusion treatment, as is usual with case hardening.
- EP 2 357 262 A1 discloses a crankshaft and a manufacturing method therefor.
- JP 2006 169637 A discloses a method of making a high strength, carburized component.
- EP 1 070 760 A2 discloses a high-pressure-resistant component and its manufacturing method.
- Steel components produced from steel used according to the invention are distinguished by a particularly homogeneous structure with a low variance in hardness. This optimally even distribution of the structural properties is also included
- the homogeneous structural condition that occurs when the steel is used according to the invention also results in low internal stresses in the component.
- the steel components produced from steel used according to the invention tend to warp and cracks or other stress-related damage at most in the course of the thermochemical hardening of the surface layer.
- a steel component which is a gear wheel, a shaft, an axle or a tool holder, with a thermochemically hardened surface layer
- a thermochemically hardened surface layer which consists of (in% by weight) 0.1-0, 30% C, up to 0.80% Si, 0.20 - 2.00% Mn, up to 4.00% Cr, 0.5 - 1.80% Mo, 0.004 - 0.020% N, up to 0, 40% S, 0.004 - 0.020% Al, up to 0.0025% B, up to 0.20% Nb, up to 0.02% Ti, up to 0.40% V, up to 0.5% Ni, 0.3% Cu, up to 1.5% Co and the remainder of iron and unavoidable impurities, with the Al content% Al, the Nb content% Nb, the Ti content% Ti, the V content % V and the N content% N of the steel meet the following conditions: % Al / 27 + % Nb / 45 + % Ti / 48 + % V / 25th > % N / 3.5
- the steel to be used according to the invention is alloyed and can be processed in such a way that the steel component that is made from it has a structure consisting of at least 80% by volume of bainite in its core area.
- the impurities of the steel to be used according to the invention which are unavoidable as a result of the production process, include all elements that are present in amounts which are ineffective in terms of alloying technology and due to the properties of interest here
- the route chosen in each case to produce the steel powder or the selected starting material (scrap) get into the steel.
- the unavoidable impurities also include P contents of up to 0.0035% by weight.
- a steel component produced from steel to be used according to the invention is thus characterized in that it has a structure consisting of at least 80% by volume of bainite.
- the rest of the structure of a maximum of 20% by volume of the total structure is taken up by residual austenite, ferrite, pearlite and / or martensite.
- the contents of non-bainitic structural constituents of a steel component made of steel to be used according to the invention are so greatly minimized that it has a completely bainitic structure in the technical sense.
- the alloy concept on which the steel to be used according to the invention is based avoids expensive alloy components, such as are usually required today for the case-hardening and tool steels used for the production of steel components in question, in order to set the required hardness.
- Carbon Carbon
- By adding 0.01% by weight in each case an increase in strength of approx. 70 MPa can be achieved.
- This effect starts in particular from a content of at least 0.09% by weight of C, in particular at least 0.12% by weight of C,.
- the steel By limiting the C content to a maximum of 0.30% by weight, in particular a maximum of 0.25% by weight, the steel has good elongation and toughness properties despite its maximized strength.
- the comparably low C content in a steel to be used according to the invention also contributes to the acceleration of the bainite transformation, so that the formation of undesirable structural components is avoided.
- An optimized effect of the presence of C in the steel to be used according to the invention can be achieved by setting the C content to 0.12-0.25% by weight.
- Si Silicon
- the Si content of a steel to be used according to the invention is therefore limited to 0.80% by weight, in order to allow the bainite transformation to take place as early as possible. At the same time, Si contents up to this upper limit contribute to increasing the strength through solid solution strengthening.
- the Si content is therefore preferably at least 0.2% by weight, in particular more than 0.45% by weight, such as at least 0.46% by weight .-%, adjusted.
- Manganese is present in contents of 0.20-2.00% by weight in the steel to be used according to the invention, in order to adjust the tensile strength and yield point by means of solid solution formation.
- a minimum content of 0.20% by weight Mn is required so that there is an increase in strength. If this effect is to be achieved particularly reliably, an Mn content of at least 0.4% by weight can be provided. Too high an Mn content would, however, lead to a delay in the bainite transformation and thus to a predominantly martensitic transformation. Therefore, the Mn content is limited to at most 2.00% by weight, particularly at most 1.5% by weight. Negative influences of the presence of Mn can be avoid particularly safely by limiting the Mn content of the steel to be used according to the invention to a maximum of 1.2% by weight.
- chromium of up to 4.00% by weight contribute to the hardenability and corrosion resistance of the steel to be used according to the invention due to the formation of special carbides and chromium nitrides during one of the nitriding treatment carried out according to the invention.
- Cr chromium
- at least 0.5% by weight or at least 0.8% by weight of Cr can be provided.
- An optimal effect of the presence of Cr results with a Cr content of at least 1.00% by weight.
- Cr contents above 4.00% by weight would promote undesirable martensite formation in the structure of the steel to be used according to the invention.
- the Cr content can be limited to up to 3% by weight or up to 2.5% by weight.
- Molybdenum (“Mo”) is present in the steel to be used according to the invention in contents of 0.5-1.8% by weight in order to delay the transformation of the structure into ferrite or pearlite and to enlarge the window for the bainite transformation. This effect occurs in particular when at least 0.6% by weight is present in the steel. With contents of more than 1.8% by weight, based on the use of the steel to be used according to the invention, which is the focus here, there is no longer any economically justifiable further increase in the positive effect of Mo. By limiting the Mo content to 1.8% by weight, the formation of a carbide phase rich in molybdenum, which would negatively affect the toughness properties, is reliably excluded. Optimal effects of Mo in the steel to be used in the present invention can be expected when the Mo content is at least 0.7% by weight. Mo contents of at most 1.5% by weight or at most 1.0% by weight have proven to be particularly effective.
- N in the contents of 0.004-0.020% by weight provided according to the invention enables the formation of nitrides and carbonitrides to increase strength and increase fine-grain resistance without embrittlement occurring.
- Al and N form aluminum nitride, which contributes to fine-grain stability.
- the content of sulfur ("S") in the steel to be used according to the invention can be up to 0.4% by weight, in particular at most 0.1% by weight, in order to support the machinability of the steel.
- S sulfur
- an S content of at least 0.001% by weight can be provided. If the S content is above 0.4% by weight, there is a risk of red brittleness.
- Optimal effects of the presence of S in the steel to be used according to the invention can be achieved with contents of 0.003-0.1% by weight.
- B in contents of up to 0.0025% by weight, in particular at least 0.0001% by weight or at least 0.0005% by weight, in the steel to be used according to the invention delays the formation of ferrite or pearlite and secures it thus the formation of the desired bainitic structure in the steel to be used according to the invention.
- B contents above 0.0025% by weight would entail the risk of embrittlement.
- the optionally present micro-alloy elements Nb, Ti and V form carbonitrides and can thus make a significant contribution to optimizing the fine-grain stability and strength of the steel to be used according to the invention.
- the alloying fine adjustment with regard to the mechanical properties and the structure of a steel used according to the invention is carried out according to the alloy concept used according to the invention via a combined microalloy made up of the elements Boron (“B”) in optional contents of up to 0.0025% by weight, in particular in contents of 0.0001-0.0025% by weight B or 0.0005-0.0025% by weight B, Nitrogen (“N”) in contents of 0.004-0.020% by weight, in particular at least 0.006% by weight N or up to 0.0150% by weight N, aluminum (“AI”) in contents of 0.004-0.020% by weight .-% and niobium (“Nb”) in optional contents of up to 0.020% by weight, in particular up to 0.015% by weight and in particular at least 0.003% by weight or at least 0.005% by weight of Nb, titanium (“ Ti ”) in optional contents of up to 0.02% by weight or up to 0.015% by weight, in particular at least 0.001% by weight or at least 0.005% by weight Ti, and vanadium (“ V ”)
- the micro-alloy elements and of aluminum In order to safely use the advantages of the presence of the micro-alloy elements and of aluminum, it can be expedient to reduce the Al content to at least 0.005% by weight, the Ti content to at least 0.001% by weight, and the V content to at least 0 , 02% by weight or the Nb content to at least 0.003% by weight.
- the micro-alloy elements V, Ti, Nb on the one hand and Al on the other hand can be present in each case in combination with one or more elements from the group "Al, V, Ti, Nb" or alone in amounts above the minimum contents mentioned.
- the contents% Al,% Nb,% Ti,% V and% N of Al, Nb, Ti, V and N are above the condition in the steel to be used according to the invention % Al / 27 + % Nb / 45 + % Ti / 48 + % V / 25th > % N / 3.5 linked together in such a way that the nitrogen contained in the steel to be used according to the invention is completely bound via the respective existing contents of Al as well as the optionally additionally added contents of Nb, Ti and V and boron can thus have a conversion-retarding effect.
- the binding of N according to the invention also enables the optionally present boron to act as a dissolved element in the matrix of the steel and suppress the formation of ferrite and / or pearlite.
- Ni up to 0.5% by weight improve the toughness of the steel to be used according to the invention. If this effect is to be used, it occurs from a Ni content of at least 0.1% by weight, in particular at least 0.15% by weight.
- the alloying elements that enter the steel to be used according to the invention via the starting material or are added in a targeted manner also include Cu, the content of which is limited to a maximum of 0.3% by weight in order to avoid negative influences in the steel to be used according to the invention.
- Co Cobalt
- contents of up to 1.5% by weight causes the bainite formation to be shifted to shorter times.
- the positive influence of Co can be used in particular with Co contents of at least 0.25% by weight, in particular at least 0.5% by weight, with Co contents of up to 1.0% by weight have proven to be particularly effective.
- a steel alloy particularly suitable for the purposes according to the invention accordingly consists of (in% by weight) 0.12 - 0.25% C, 0.20 - 0.80% Si, 0.40 - 1.20% Mn, 1.0-3.0% Cr, 0.5-1.8% Mo, 0.004-0.020% N, up to 0.40% S, 0.004-0.020% Al, 0.0005-0.0025% B, up to 0.10% Nb, up to 0.015% Ti, up to 0.20% V, up to 0.5% Ni, and / or up to 1.5% Co, the remainder being iron and unavoidable impurities, for which the explanations given above in this regard also apply here.
- the steel to be used for the production of steel components is suitable for all of the thermochemical diffusion processes "carburizing", “carbonitriding”, “nitriding” or “nitrocarburizing” described in the above mentioned leaflets 452 and 477.
- carburizing or carbonitriding is carried out as a thermochemical diffusion treatment.
- carburizing carburizing, carbonitriding
- hardening takes place during conventional case hardening in accordance with the hardening methods "direct hardening (type A)", “single hardening (type B)", “isothermal hardening”, which are also described in detail in leaflet 452 Converting (Type C) "or” Double Hardening (Type D) ".
- direct hardening type A
- the steel component is quenched directly from the heat of the preceding carburizing or carbonitriding treatment.
- the steel component With single hardening (type B), after the previous carburizing or carbonitriding treatment, the steel component is first cooled to room temperature and then heated again to an austenitizing temperature above the Ac1 and below the Ac3 temperature of the steel and then quenched.
- type C hardening after isothermal conversion
- the steel component is initially cooled from the heat of the preceding carburizing or carbonitriding treatment to a temperature range in which certain carbide precipitates are formed, and then, starting from this temperature range, it is again heated through to an austenitizing temperature above the Ac1 and below the Ac3 temperature of the steel, in order then to be quenched.
- double hardening (type D) after the steel component has been cooled to room temperature from the heat of the previous carburizing or carbonitriding treatment, as with single hardening type A, it goes through a hardening process twice, which is only performed once with single hardening type A.
- the cooling to be carried out must in any case be set so that, on the one hand, the carburizing or carbonitriding hardness-increasing precipitates on the carburized edge layer and, in the non-carburized core area of the component, a structure consisting of at least 80% by volume of bainite according to the stipulation explained above.
- the temperature range of 800-500 ° C. must be passed through in a time t8 / 5 of at least 6 s, in particular at least 10 s, and at most 600 s, during the cooling process.
- thermochemical diffusion treatment is to be carried out as nitriding or nitrocarburizing for the purpose of forming the hardened surface layer, which is not covered by the present invention, then the procedure described in detail in leaflet 477 can be selected.
- the steel component After being heated to an austenitizing temperature above the Ac3 temperature of the steel from which the steel component is made, the steel component is continuously cooled so that the temperature range of 800 - 500 ° C in a time t8 / 5 of at least 6 s, in particular at least 10 s, and a maximum of 1000 s, in particular a maximum of 200 s, is run through in order to form in the component a structure consisting of at least 80% by volume of bainite in accordance with the stipulation explained above.
- the nitriding or nitrocarburizing step in which the steel component is placed in a nitrogen or nitrogen and carbon-containing atmosphere at a temperature below the Ac1 temperature of the steel from which the steel component is made, in accordance with the instructions and stipulations contained in leaflet 477 exists, the lying temperature is maintained and then cooled.
- the duration for which the steel component is held under the carbonaceous medium during the carburizing step is set in a manner known per se, depending on the size of the component and taking into account the carbonaceous medium used and the temperature at which the carburization is carried out, as follows chosen so that a carburized surface layer with a thickness lying within the specifications according to the invention is achieved.
- the shortest duration can be indicated, for example, for smaller components, such as gear parts, in particular gears, shafts and axles, of automobile transmissions and the like, whereas the longest duration can be appropriate for large components, such as gear parts, in particular gears, shafts and axles, of large gears that are intended for slewing bearings such as those used in wind turbines or ship propulsion systems.
- the temperature at which the steel component is kept during the carburizing step (step b.1) is typically up to 950 ° C.
- the carburizing process can be accelerated and the duration required for the required carburizing can be shortened accordingly.
- step b1) the steel component is hardened in a hardening step b2) heated to an austenitizing temperature which is at least 20 ° C above the Ac1 temperature and below the Ac3 temperature of the steel from which the steel component is made, and based on the austenitizing temperature with a cooling rate of 0.5 - 50 K / s , in particular at least 1.5 K / s or more than 1.5 K / s, cooled to room temperature.
- the steel component made of steel according to the invention can optionally be subjected to a stress-relieving anneal between steps b1) and b2), in which it is heated for a period of 15 - 120 min Range of 150 - 680 ° C is maintained.
- the steel component can optionally be subjected to a tempering treatment in a manner known per se, in which it is kept at a temperature of 150-275 ° C for a period of 30-180 minutes and then cooled to room temperature in an uncontrolled manner becomes.
- a tempering treatment in a manner known per se, in which it is kept at a temperature of 150-275 ° C for a period of 30-180 minutes and then cooled to room temperature in an uncontrolled manner becomes.
- Such tempering can further reduce the risk of cracking.
- a case-hardened steel component according to the invention can be produced that is made from the steel to be used according to the invention, which consists of (in% by weight) 0.12-0.25% C, 0.20-0.80% Si, 0.40-1.20% Mn, 1.0-3.0% Cr, 0.5-1.8% Mo, 0.004-0.020% N, up to 0.40% S, 0.004-0.020% AI, 0.0001 - 0.0025% B, up to 0.10% Nb, up to 0.01% Ti, up to 0.20% V, up to 0.5% Ni, up to 1.0% Co and as the remainder iron and unavoidable impurities, is made and a surface layer with a hardness of 500 - 800 HV and according to the invention in its core area consists of at least 80% by volume of bainite, which consists of highly tempered bainite, which comes from the structure that the steel component after insertion (step b.1) and before hardening (step b.2 ), and newly formed bainite
- This structural composition results from hardening of the components according to the invention in the two-phase area.
- the existing bainitic structural components that have arisen from the "old", i.e. prior to hardening (step b.2) can be separated from the "new" bainitic structural components that have arisen in the course of the hardening by a slight brown coloration of the new bainite from the old,
- highly tempered bainite which has a grayish color and an indicated grainy structure.
- the structure of a component that has gone through the above-explained case hardening process modified in accordance with the invention is characterized in that it has a Charpy-V notch impact energy of more than 40 J, in particular more than 40 J, determined in accordance with DIN EN 10045, in the core area of the steel component 60 J.
- Cr, V, Nb or Ti contents of the steel used in accordance with the invention arise from the formation of nitrides for a high surface hardness.
- the bainitic core area (matrix) experiences an increase in hardness of approx. 100 - 150 MPa during nitriding or nitrocarboring due to the formation of Special carbides, in particular from the Mo content (molybdenum-rich carbide) contained in the steel.
- the specifically set parameters "duration” and "temperature” of the nitriding or nitrocarburizing treatment are set in a manner known per se, depending on the component size, so that a hardened surface layer is achieved with a thickness within the specifications according to the invention.
- steps B1) and B2) on the steel component which is still relatively soft after step B1), in order to reduce tool wear compared to machining in the final hardened state Reduce.
- the steel to be used according to the invention is particularly suitable for the production of surface-hardened gear wheels, axles, shafts or tool holders for cutting tools produced by powder metallurgy.
- a gear was formed from steel S1.
- the gear was then subjected to a conventional manner in accordance with the procedure described in leaflet 452, initially to carburizing at 920 ° C. over a period of 300 min under a carbon-containing atmosphere composed in a manner known per se for this purpose.
- the gear is through thermochemical diffusion created a carburized surface layer with a thickness of 520 ⁇ m.
- the gearwheel was then cooled to room temperature, the cooling rate being 2 K / s and the critical temperature range of 800-500 ° C. being passed through in a t8 / 5 time of 10 minutes.
- the resulting gear was then heated to an austenitizing temperature of 920 ° C. and held at this temperature for 30 minutes.
- the gear was then quenched at a cooling rate of 2 K / s.
- the critical temperature range of 800 - 500 ° C was passed through in a t8 / 5 time of 600 s.
- the gear wheel case-hardened in this way had a hardness of 750 HV on the surface of its hardened edge layer and a completely bainitic structure in its core area (matrix) bearing the hardened edge layer.
- the gear was then quenched in oil to room temperature.
- the critical temperature range of 800 - 500 ° C was passed through in a t8 / 5 time of 17 s.
- the gearwheel then went through a stress-relieving heat treatment, in which it was held at 650 ° C. for one hour in order to relieve the stresses that had arisen during the previously performed carburizing treatment.
- the component was heated in a hardening step to an austenitizing temperature and held at this temperature for one hour, which was 40 ° C. below the Ac3 temperature of steel S2, the Ac3 temperature of steel S2 previously known per se Way has been determined by means of a dilatometer experiment.
- the gearwheel was then quenched in oil again, so that here too the t8 / 5 time was 17 s.
- the gear was subjected to a conventional tempering in which it was held at 180 ° C. for one hour.
- the case-hardened gear wheel had a hardness of 750 HV on the surface of its hardened edge layer and a completely bainitic structure in its core area (matrix) bearing the hardened edge layer, which consisted of newly formed and old, highly tempered bainite.
- a gear with a diameter of less than 40 mm was formed from steel S3.
- the gearwheel was then first subjected to carburizing at 920 ° C. over a period of 30 minutes under a carbon-containing atmosphere that is usually used for this purpose.
- a carbonized (carburized) surface layer with a thickness of 530 ⁇ m was created on the gear wheel by thermochemical diffusion.
- the gear was then quenched in water at a cooling rate of 3 K / s to room temperature.
- the critical temperature range of 800 - 500 ° C was passed through in a t8 / 5 time of 300 s.
- the component was heated in a hardening step to an austenitizing temperature and held at this temperature for one hour, which was 920.degree.
- the gearwheel was then quenched in water, the t8 / 5 time being 300 s.
- the gear wheel case-hardened in this way had a hardness of 760 HV on the surface of its hardened edge layer and a completely bainitic structure in its core area (matrix) bearing the hardened edge layer.
Description
Die Erfindung betrifft ein Verfahren zur Herstellung eines einsatzgehärteten Stahlbauteils. Wenn nachfolgend "%"-Angaben zu Legierungen oder Stahlzusammensetzungen gemacht werden, so beziehen diese sich jeweils auf das Gewicht, soweit nichts ausdrücklich anderes angegeben ist.The invention relates to a method for producing a case-hardened steel component. If "%" information is given below about alloys or steel compositions, these relate to weight, unless expressly stated otherwise.
Sämtliche der im vorliegenden Text angegebenen mechanischen Eigenschaften des erfindungsgemäß zu verwendenden Stahls und der gegebenenfalls zum Vergleich angeführten Stähle sind, soweit nicht anders angegeben, nach DIN EN ISO 6892-1 bestimmt worden.Unless otherwise stated, all of the mechanical properties of the steel to be used according to the invention and of the steels that may be listed for comparison have been determined in accordance with DIN EN ISO 6892-1.
Bei den hier betrachteten Stahlbauteilen handelt es sich typischerweise um Bauelemente, die in der Praxis mit anderen Bauteilen in einer Abwälz- oder Abrollbewegung in metallischem Kontakt kommen und daher im Bereich ihrer Kontaktfläche hohen mechanischen Belastungen ausgesetzt sind. Typische Beispiele für solche Bauteile sind Zahnräder, Wellen oder Achsen. Zu vergleichbaren Belastungen kann es bei Haltern von Werkzeugen, beispielsweise Schneidwerkzeugen und desgleichen, im Bereich der Anlageflächen zwischen dem Halter und dem jeweiligen Werkzeug kommen.The steel components considered here are typically components that in practice come into metallic contact with other components in a rolling or rolling movement and are therefore exposed to high mechanical loads in the area of their contact surface. Typical examples of such components are gears, shafts or axles. Comparable loads can occur in the case of tool holders, for example cutting tools and the like, come in the area of the contact surfaces between the holder and the respective tool.
Dabei besteht die besondere Herausforderung, dass solche Stahlbauteile in der Regel komplex geformt sind und nur durch aufwändige spanabhebende Bearbeitung gefertigt werden können. Eine solche spanabhebende Bearbeitung lässt sich dann besonders wirtschaftlich durchführen, wenn die Bauteile aus Stählen mit niedrigen Kohlenstoffgehalten bestehen, also eine geringe Härte besitzen. Gleichzeitig erweist sich eine vergleichbar geringe Härte und damit einhergehend hohe Zähigkeit des Stahls, aus denen solche Bauteile bestehen, im Hinblick auf deren Dauerfestigkeit insbesondere unter Betriebsbedingungen als günstig, in denen die vom jeweiligen Bauteil aufzunehmenden Belastungen dynamisch auftreten.The particular challenge here is that such steel components are usually complexly shaped and can only be manufactured by means of complex machining. Such machining can be carried out particularly economically if the components are made of steels with a low carbon content, i.e. have a low hardness. At the same time, a comparably low hardness and the associated high toughness of the steel from which such components are made are found to be favorable with regard to their fatigue strength, especially under operating conditions in which the loads to be absorbed by the respective component occur dynamically.
Beispielsweise für die Zahnradfertigung werden heute typischerweise Einsatzstähle verwendet, zu denen exemplarisch die Stähle mit der 16MnCr5 / 16MnCrS5 (Werkstoffnummern 1.7131 /1.7139) und 18CrNiMo7-6 (Werkstoffnummer 1.6587) zu nennen sind.For example, case hardening steels are typically used today for gear manufacturing, examples of which are the steels with 16MnCr5 / 16MnCrS5 (material numbers 1.7131 /1.7139) and 18CrNiMo7-6 (material number 1.6587).
Werkzeughalter, wie beispielsweise Halter für pulvermetallurgisch erzeugte Schneidkörper, werden häufig aus relativ teuren Werkzeugstählen, wie Stählen mit den Werkstoffnummern 1.2311, 1.2312, 1.2738, 1.2343 oder 1.2343, hergestellt.Tool holders, such as holders for cutting bodies produced by powder metallurgy, are often made from relatively expensive tool steels, such as steels with the material numbers 1.2311, 1.2312, 1.2738, 1.2343 or 1.2343.
Es sind verschiedene Wärmebehandlungsverfahren bekannt, mit denen sich die Lebensdauer von aus solchen von Haus aus vergleichbar weichen Stählen gefertigten Werkstücken und Werkzeugen verbessern lassen. Diese Verfahren basieren darauf, dass in einer Randschicht, die die im Gebrauch belastete Kontaktfläche trägt, eine höhere Härte erzeugt wird, als im die betreffende Randschicht tragenden Kernbereich des Bauteils, in dem auch nach der Wärmebehandlung weiterhin eine hohe Zähigkeit vorliegt.Various heat treatment processes are known which can be used to improve the service life of workpieces and tools made from steels that are made from steels that are comparatively soft. These methods are based on the fact that a higher hardness is generated in an edge layer that bears the contact surface that is stressed during use than in the core area of the component bearing the respective edge layer, in which a high level of toughness is still present even after the heat treatment.
Wie in den Merkblättern 452 "
Zu den gängigen Verfahren, mit denen sich insbesondere Zahnräder und im Gebrauch vergleichbar belastete Bauteile mit einer gehärteten Randschicht versehen lassen, gehören das Einsatzhärten (s. Merkblatt 452), bei dem zunächst die Randschicht des Stahlbauteils eine Carburierungs- bzw. Carbonitrierungsbehandlung eine Erhöhung des Kohlenstoffgehalts und anschließend das Bauteil ein Härten durchläuft, um in der gehärteten Randschicht eine maximale Härte zu erzielen, und das Nitrieren bzw. Nitrocarburieren (s. Merkblatt 477), bei dem die Härtezunahme der Randschicht wesentlich durch eindiffundierten Stickstoff erzielt wird, wobei eine zusätzliche Härteerhöhung durch in Kombination mit dem Stickstoff eindiffundierten Kohlenstoff erzielt werden kann.Case hardening (see leaflet 452), in which the surface layer of the steel component is first subjected to a carburizing or carbonitriding treatment to increase the carbon content, is one of the common methods with which gearwheels and components that are subjected to comparable loads in use can be provided with a hardened surface layer and then the component undergoes hardening in order to achieve maximum hardness in the hardened surface layer, and nitriding or nitrocarburizing (see leaflet 477), in which the increase in hardness of the surface layer is essentially achieved by diffused nitrogen, with an additional increase in hardness by can be achieved in combination with the nitrogen diffused carbon.
Vor dem Hintergrund des voranstehend erläuterten Standes der Technik bestand die Aufgabe der Erfindung darin, ein Verfahren zum Herstellen eines Stahlbauteils zu nennen, das optimale Eigenschaftskombination bei solchen durch eine thermochemische Diffusionsbehandlung randschichtgehärteten Stahlbauteilen ergibt, die im Gebrauch im wälzenden oder abrollenden Kontakt mit einem anderen Bauteil stehen.Against the background of the prior art explained above, the object of the invention was to name a method for producing a steel component which has the optimum combination of properties in those surface-hardened by a thermochemical diffusion treatment Steel components that are in rolling or rolling contact with another component during use.
Ebenso ist randschichtgehärtetes Stahlbauteil offenbart, das eine im Hinblick auf seine Dauerfestigkeit optimale Kombination aus Härte in seiner Randschicht und Zähigkeit in seinem die Randschicht tragenden Kernbereich besitzt.A surface-hardened steel component is also disclosed, which has an optimal combination of hardness in its surface layer and toughness in its core area bearing the surface layer with regard to its fatigue strength.
Zur Herstellung von randschichtgehärteten Stahlbauteilen, die einen optimal zähen Kernbereich aufweisen die Erfindung das Verfahren nach Anspruch 1 vor.For the production of surface-hardened steel components which have an optimally tough core area, the invention includes the method according to claim 1.
Vorteilhafte Ausgestaltungen der Erfindung sind in den abhängigen Ansprüchen angegeben und werden nachfolgend wie der allgemeine Erfindungsgedanke im Einzelnen erläutert.Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below, like the general inventive concept.
Der erfindungsgemäß zu verwendende Stahl eröffnet einen robusten und kostengünstigen Fertigungsweg für die Erzeugung von durch eine thermochemische Diffusionsbehandlung randschichtzuhärtenden Stahlbauteilen, nämlich Zahnräder, Achsen, Wellen oder Werkzeughalter mit speziellen Anwendungsbedingungen. Dabei weisen die aus erfindungsgemäß verwendetem Stahl erzeugten Bauteile nach der jeweils für ihre thermochemische Randschichthärtung durchgeführten Wärmebehandlung eine höhere Zähigkeit in ihrem Kernbereich, auch "Matrix" genannt, auf, als dies bei heute üblicherweise zu diesem Zweck verwendeten Stählen der Fall ist.The steel to be used according to the invention opens up a robust and cost-effective production route for the production of steel components to be surface hardened by a thermochemical diffusion treatment, namely gear wheels, axles, shafts or tool holders with special application conditions. After the heat treatment carried out for their thermochemical surface hardening, the components produced from steel used according to the invention have a higher toughness in their core area, also called "matrix", than is the case with steels commonly used for this purpose today.
Die Erfindung geht von der Erkenntnis aus, dass sich eine Modifikation eines ein bainitisches Gefüge bildenden Stahls, der grundsätzlich aus der Veröffentlichung
In dieser Hinsicht erweist es sich als besonders vorteilhaft, dass der aus der der Veröffentlichung der voranstehend genannten Europäischen Patentanmeldung an sich bekannte Stahl, wie in der
Aus erfindungsgemäß verwendetem Stahl erzeugte Stahlbauteile, also Zahnräder, Wellen, Achsen oder Werkzeughalter, zeichnen sich durch ein besonders homogenes Gefüge mit einer geringen Varianz der Härte aus. Diese optimal gleichmäßige Verteilung der Gefügeeigenschaften liegt auch bei unterschiedlichsten Abmessungen der aus erfindungsgemäß zu verwendenden Stahl herzustellenden Stahlbauteile und bei den durch diese Abmessungsunterschiede bedingten, über eine große Spanne variierenden Abkühlbedingungen vor. Der bei erfindungsgemäßer Verwendung des Stahls sich einstellende homogene Gefügezustand bedingt darüber hinaus geringe Eigenspannungen im Bauteil. Dementsprechend neigen die aus erfindungsgemäß verwendetem Stahl erzeugten Stahlbauteile im Zuge der thermochemischen Randschichthärtung allenfalls geringfügig zu Verzug und zur Entstehung von Rissen oder anderen spannungsbedingten Schäden.Steel components produced from steel used according to the invention, that is to say gear wheels, shafts, axles or tool holders, are distinguished by a particularly homogeneous structure with a low variance in hardness. This optimally even distribution of the structural properties is also included The most varied dimensions of the steel components to be produced from steel to be used according to the invention and the cooling conditions that are caused by these dimensional differences and vary over a large range. The homogeneous structural condition that occurs when the steel is used according to the invention also results in low internal stresses in the component. Correspondingly, the steel components produced from steel used according to the invention tend to warp and cracks or other stress-related damage at most in the course of the thermochemical hardening of the surface layer.
Erfindungsgemäß wird somit zur Herstellung eines Stahlbauteils, bei dem es sich um ein Zahnrad, eine Welle, eine Achse oder einen Werkzeughalter handelt, mit einer thermochemisch gehärteten Randschicht ein Stahl verwendet, der aus (in Gew.-%) 0,1 - 0,30 % C, bis zu 0,80 % Si, 0,20 - 2,00 % Mn, bis zu 4,00 % Cr, 0,5 - 1,80 % Mo, 0,004 - 0,020 % N, bis zu 0,40 % S, 0,004 - 0,020 % Al, bis zu 0,0025 % B, bis zu 0,20 % Nb, bis zu 0,02 % Ti, bis zu 0,40 % V, bis zu 0,5 % Ni, 0,3 % Cu, bis zu 1,5 % Co und als Rest aus Eisen und unvermeidbaren Verunreinigungen, besteht, wobei der Al-Gehalt %Al, der Nb-Gehalt %Nb, der Ti-Gehalt %Ti, der V-Gehalt %V und der N-Gehalt %N des Stahls folgende Bedingung erfüllen: 
Der erfindungsgemäß zu verwendende Stahl ist dabei so legiert und lässt sich so verarbeiten, dass das Stahlbauteil, das aus ihm hergestellt ist, in seinem Kernbereich ein zu mindestens 80 Vol.-% aus Bainit bestehendes Gefüge aufweist. Dabei gehören zu den herstellungsbedingt unvermeidbaren Verunreinigungen des erfindungsgemäß zu verwendenden Stahls alle Elemente, die in Bezug auf die hier interessierenden Eigenschaften in legierungstechnisch unwirksamen Mengen vorhanden sind und aufgrund der jeweils gewählten Route zur Erzeugung des Stahlpulvers oder des jeweils gewählten Ausgangsmaterials (Schrott) in den Stahl gelangen. Insbesondere gehören zu den unvermeidbaren Verunreinigungen auch Gehalte an P von bis zu 0,0035 Gew.-%.The steel to be used according to the invention is alloyed and can be processed in such a way that the steel component that is made from it has a structure consisting of at least 80% by volume of bainite in its core area. The impurities of the steel to be used according to the invention, which are unavoidable as a result of the production process, include all elements that are present in amounts which are ineffective in terms of alloying technology and due to the properties of interest here The route chosen in each case to produce the steel powder or the selected starting material (scrap) get into the steel. In particular, the unavoidable impurities also include P contents of up to 0.0035% by weight.
Ein aus erfindungsgemäß zu verwendendem Stahl erzeugtes Stahlbauteil zeichnet sich somit dadurch aus, dass es ein zu mindestens 80 Vol.-% aus Bainit bestehendes Gefüge besitzt. Das übrige Gefüge von in Summe höchstens 20 Vol.-% des Gesamtgefüges wird dabei von Restaustenit, Ferrit, Perlit und/oder Martensit eingenommen. Typischerweise sind jedoch die Gehalte an nicht bainitschen Gefügebestandteilen eines aus erfindungsgemäß zu verwendendem Stahl bestehenden Stahlbauteils so stark minimiert, dass in ihm im technischen Sinne ein vollständig bainitisches Gefüge vorliegt.A steel component produced from steel to be used according to the invention is thus characterized in that it has a structure consisting of at least 80% by volume of bainite. The rest of the structure of a maximum of 20% by volume of the total structure is taken up by residual austenite, ferrite, pearlite and / or martensite. Typically, however, the contents of non-bainitic structural constituents of a steel component made of steel to be used according to the invention are so greatly minimized that it has a completely bainitic structure in the technical sense.
Das dem erfindungsgemäß zu verwendenden Stahl zu Grund liegende Legierungskonzept vermeidet teure Legierungsbestandteile, wie sie heute üblicherweise bei den für die Herstellung von Stahlbauteilen der hier in Rede stehenden verwendeten Einsatz- und Werkzeugstähle benötigt werden, um die erforderliche Härte einzustellen. Dies gelingt dadurch, dass die Legierungselemente und deren Gehalte beim erfindungsgemäß zu verwendenden Stahl wie folgt ausgewählt sind:
Kohlenstoff ("C") ist im erfindungsgemäß zu verwendenden Stahl in Gehalten von 0,1 - 0,3 Gew.-% enthalten, um durch Karbidbildung zur Steigerung der Festigkeit des Werkstoffs beizutragen. So kann durch die Zugabe von jeweils 0,01 Gew.-% eine Festigkeitserhöhung um jeweils ca. 70 MPa bewirkt werden. Dieser Effekt setzt insbesondere ab einem Gehalt von mindestens 0,09 Gew.-% C, insbesondere mindestens 0,12 Gew.-% C, ein. Durch die Begrenzung des C-Gehalts auf höchstens 0,30 Gew.-%, insbesondere höchstens 0,25 Gew.-%, wird dabei erreicht, dass der Stahl trotz seiner maximierten Festigkeit gute Dehnungs- und Zähigkeitseigenschaften besitzt. Gleichzeitig trägt der vergleichbar geringe C-Gehalt bei einem erfindungsgemäß zu verwendenden Stahl auch zur Beschleunigung der Bainitumwandlung bei, so dass die Entstehung von unerwünschten Gefügebestandteilen vermieden wird. Eine optimierte Wirkung der Anwesenheit von C im erfindungsgemäß zu verwendenden Stahl kann dadurch erreicht werden, dass der C-Gehalt auf 0,12 - 0,25 Gew.-% eingestellt wird.The alloy concept on which the steel to be used according to the invention is based avoids expensive alloy components, such as are usually required today for the case-hardening and tool steels used for the production of steel components in question, in order to set the required hardness. This is achieved in that the alloying elements and their contents in the steel to be used according to the invention are selected as follows:
Carbon ("C") is contained in the steel to be used according to the invention in contents of 0.1-0.3% by weight in order to contribute to increasing the strength of the material through carbide formation. By adding 0.01% by weight in each case, an increase in strength of approx. 70 MPa can be achieved. This effect starts in particular from a content of at least 0.09% by weight of C, in particular at least 0.12% by weight of C,. By limiting the C content to a maximum of 0.30% by weight, in particular a maximum of 0.25% by weight, the steel has good elongation and toughness properties despite its maximized strength. At the same time, the comparably low C content in a steel to be used according to the invention also contributes to the acceleration of the bainite transformation, so that the formation of undesirable structural components is avoided. An optimized effect of the presence of C in the steel to be used according to the invention can be achieved by setting the C content to 0.12-0.25% by weight.
Silizium ("Si") unterdrückt im erfindungsgemäß zu verwendenden Stahl die Zementitbildung und verschiebt die Ferritbildung zu kürzeren Zeiten. Der Si-Gehalt eines erfindungsgemäß zu verwendenden Stahls ist deshalb auf 0,80 Gew.-%, beschränkt, um die Bainitumwandlung möglichst früh ablaufen zu lassen. Gleichzeitig tragen Si-Gehalte bis zu dieser Obergrenze zur Erhöhung der Festigkeit durch Mischkristallverfestigung bei. Um die vorteilhaften Wirkungen von Si im erfindungsgemäß zu verwendenden Stahl besonders sicher nutzen können, ist der Si-Gehalt daher vorzugsweise auf mindestens 0,2 Gew.-%, insbesondere mehr als 0,45 Gew.-%, wie mindestens 0,46 Gew.-%, eingestellt.Silicon ("Si") suppresses the formation of cementite in the steel to be used according to the invention and shifts the formation of ferrite to shorter times. The Si content of a steel to be used according to the invention is therefore limited to 0.80% by weight, in order to allow the bainite transformation to take place as early as possible. At the same time, Si contents up to this upper limit contribute to increasing the strength through solid solution strengthening. In order to be able to use the advantageous effects of Si in the steel to be used according to the invention particularly reliably, the Si content is therefore preferably at least 0.2% by weight, in particular more than 0.45% by weight, such as at least 0.46% by weight .-%, adjusted.
Mangan ("Mn") ist in Gehalten von 0,20 - 2,00 Gew.-% im erfindungsgemäß zu verwendenden Stahl vorhanden, um die Zugfestigkeit und Streckgrenze durch Mischkristallbildung einzustellen. Ein Mindestgehalt von 0,20 Gew.-% Mn ist erforderlich, damit es zu einer Festigkeitssteigerung kommt. Soll dieser Effekt besonders sicher erreicht werden, so kann ein Mn-Gehalt von mindestens 0,4 Gew.-% vorgesehen werden. Zu hohe Mn-Gehalte würden jedoch zur Verzögerung der Bainitumwandlung und damit zu einer überwiegend martensitischen Umwandlung führen. Daher ist der Mn-Gehalt auf höchstens 2,00 Gew.-%, insbesondere höchstens 1,5 Gew.-%, beschränkt. Negative Einflüsse der Anwesenheit von Mn lassen sich besonders sicher vermeiden, indem der Mn-Gehalt beim erfindungsgemäß zu verwendenden Stahl auf maximal 1,2 Gew.-% beschränkt wird.Manganese ("Mn") is present in contents of 0.20-2.00% by weight in the steel to be used according to the invention, in order to adjust the tensile strength and yield point by means of solid solution formation. A minimum content of 0.20% by weight Mn is required so that there is an increase in strength. If this effect is to be achieved particularly reliably, an Mn content of at least 0.4% by weight can be provided. Too high an Mn content would, however, lead to a delay in the bainite transformation and thus to a predominantly martensitic transformation. Therefore, the Mn content is limited to at most 2.00% by weight, particularly at most 1.5% by weight. Negative influences of the presence of Mn can be avoid particularly safely by limiting the Mn content of the steel to be used according to the invention to a maximum of 1.2% by weight.
Optional vorhandene Gehalte an Chrom ("Cr") von bis zu 4,00 Gew.-% tragen durch die Bildung von Sonderkarbiden und Chromnitriden bei einer der erfindungsgemäß durchgeführten Nitrierbehandlung zur Härtbarkeit und Korrosionsbeständigkeit des erfindungsgemäß zu verwendenden Stahls bei. Hierzu können beispielsweise mindestens 0,5 Gew.-% oder mindestens 0,8 Gew.-% Cr vorgesehen sein. Eine optimale Wirkung der Anwesenheit von Cr ergibt sich bei einem Cr-Gehalt von mindestens 1,00 Gew.-%. Oberhalb von 4,00 Gew.-% liegende Cr-Gehalte würden eine unerwünschte Martensitbildung im Gefüge des erfindungsgemäß zu verwendenden Stahl begünstigen. Um dies sicher zu vermeiden, kann der Cr-Gehalt auf bis zu 3 Gew.-% oder bis zu 2,5 Gew.-% beschränkt werden.Optionally present contents of chromium ("Cr") of up to 4.00% by weight contribute to the hardenability and corrosion resistance of the steel to be used according to the invention due to the formation of special carbides and chromium nitrides during one of the nitriding treatment carried out according to the invention. For this purpose, for example, at least 0.5% by weight or at least 0.8% by weight of Cr can be provided. An optimal effect of the presence of Cr results with a Cr content of at least 1.00% by weight. Cr contents above 4.00% by weight would promote undesirable martensite formation in the structure of the steel to be used according to the invention. In order to safely avoid this, the Cr content can be limited to up to 3% by weight or up to 2.5% by weight.
Molybdän ("Mo") ist im erfindungsgemäß zu verwendenden Stahl in Gehalten von 0,5 - 1,8 Gew.-% vorhanden, um die Umwandlung des Gefüges in Ferrit oder Perlit zu verzögern und das Fenster für die Bainitumwandlung zu vergrößern. Diese Wirkung tritt insbesondere dann ein, wenn mindestens 0,6 Gew.-% im Stahl vorhanden sind. Bei Gehalten von mehr als 1,8 Gew.-% tritt bezogen auf die hier im Mittelpunkt stehende Nutzung des erfindungsgemäß zu verwendenden Stahl keine wirtschaftlich vertretbare weitere Steigerung der positiven Wirkung von Mo mehr ein. Durch die Begrenzung des Mo-Gehalts auf 1,8 Gew.-% wird die Bildung einer molybdänreichen Karbidphase sicher ausgeschlossen, welche die Zähigkeitseigenschaften negativ beeinflussen würde. Optimale Wirkungen von Mo im erfindungsgemäß zu verwendenden Stahl können erwartet werden, wenn der Mo-Gehalt mindestens 0,7 Gew.-% beträgt. Als besonders effektiv haben sich dabei Mo-Gehalte von höchstens 1,5 Gew.-% oder höchstens 1,0 Gew.-% erwiesen.Molybdenum ("Mo") is present in the steel to be used according to the invention in contents of 0.5-1.8% by weight in order to delay the transformation of the structure into ferrite or pearlite and to enlarge the window for the bainite transformation. This effect occurs in particular when at least 0.6% by weight is present in the steel. With contents of more than 1.8% by weight, based on the use of the steel to be used according to the invention, which is the focus here, there is no longer any economically justifiable further increase in the positive effect of Mo. By limiting the Mo content to 1.8% by weight, the formation of a carbide phase rich in molybdenum, which would negatively affect the toughness properties, is reliably excluded. Optimal effects of Mo in the steel to be used in the present invention can be expected when the Mo content is at least 0.7% by weight. Mo contents of at most 1.5% by weight or at most 1.0% by weight have proven to be particularly effective.
Die Anwesenheit von N in den erfindungsgemäß vorgesehenen Gehalten von 0,004 - 0,020 Gew.-% ermöglicht die Bildung von Nitriden und Karbonitriden zur Festigkeitssteigerung und Erhöhung der Feinkornbeständigkeit, ohne dass es zur Versprödung kommt. So bildet Al mit N Aluminiumnitrid, das zur Feinkornstabilität beiträgt.The presence of N in the contents of 0.004-0.020% by weight provided according to the invention enables the formation of nitrides and carbonitrides to increase strength and increase fine-grain resistance without embrittlement occurring. Thus, Al and N form aluminum nitride, which contributes to fine-grain stability.
Der Gehalt an Schwefel ("S") kann im erfindungsgemäß zu verwendenden Stahl bis zu 0,4 Gew.-%, insbesondere höchstens 0,1 Gew.-%, betragen, um die Zerspanbarkeit des Stahls zu unterstützen. Zu diesem Zweck kann ein S-Gehalt von mindestens 0,001 Gew.-% vorgesehen sein. Bei oberhalb von 0,4 Gew.-% liegenden S-Gehalten besteht die Gefahr der Entstehung von Rotbrüchigkeit. Optimale Wirkungen der Anwesenheit von S im erfindungsgemäß zu verwendenden Stahl können bei Gehalten von 0,003 - 0,1 Gew.-% erzielt werden.The content of sulfur ("S") in the steel to be used according to the invention can be up to 0.4% by weight, in particular at most 0.1% by weight, in order to support the machinability of the steel. For this purpose, an S content of at least 0.001% by weight can be provided. If the S content is above 0.4% by weight, there is a risk of red brittleness. Optimal effects of the presence of S in the steel to be used according to the invention can be achieved with contents of 0.003-0.1% by weight.
Die Anwesenheit von B in Gehalten von bis zu 0,0025 Gew.-%, insbesondere mindestens 0,0001 Gew.-% oder mindestens 0,0005 Gew.-%, im erfindungsgemäß zu verwendenden Stahl verzögert die Entstehung von Ferrit oder Perlit und sichert so die Entstehung des angestrebten bainitischen Gefüges im erfindungsgemäß zu verwendenden Stahl ab. Oberhalb von 0,0025 Gew.-% liegende B-Gehalte würden die Gefahr einer Versprödung mit sich bringen. Die jeweils optional vorhandenen Mikrolegierungselemente Nb, Ti und V bilden Karbonitride und können so einen wesentlichen Beitrag zur Optimierung der Feinkornstabilität und Festigkeit des erfindungsgemäß zu verwendenden Stahls leisten.The presence of B in contents of up to 0.0025% by weight, in particular at least 0.0001% by weight or at least 0.0005% by weight, in the steel to be used according to the invention delays the formation of ferrite or pearlite and secures it thus the formation of the desired bainitic structure in the steel to be used according to the invention. B contents above 0.0025% by weight would entail the risk of embrittlement. The optionally present micro-alloy elements Nb, Ti and V form carbonitrides and can thus make a significant contribution to optimizing the fine-grain stability and strength of the steel to be used according to the invention.
Die legierungstechnische Feinjustierung in Bezug auf die mechanischen Eigenschaften und die Gefügebeschaffenheit eines erfindungsgemäß verwendeten Stahls erfolgt nach dem erfindungsgemäß verwendeten Legierungskonzept über eine kombinierte Mikrolegierung aus den Elementen Bor ("B") in optionalen Gehalten von bis zu 0,0025 Gew.-%, insbesondere in Gehalten von 0,0001 - 0,0025 Gew.-% B oder 0,0005 - 0,0025 Gew.-% B, Stickstoff ("N") in Gehalten von 0,004 - 0,020 Gew.-%, insbesondere mindestens 0,006 Gew.-% N oder bis zu 0,0150 Gew.-% N, Aluminium ("AI") in Gehalten von 0,004 - 0,020 Gew.-% sowie Niob ("Nb") in optionalen Gehalten von bis zu 0,020 Gew.-%, insbesondere bis zu 0,015 Gew.-% und insbesondere mindestens 0,003 Gew.-% oder mindestens 0,005 Gew.-% Nb, Titan ("Ti") in optionalen Gehalten von bis zu 0,02 Gew.-% oder bis zu 0,015 Gew.-%, insbesondere mindestens 0,001 Gew.-% oder mindestens 0,005 Gew.-% Ti, und Vanadium ("V") in optionalen Gehalten von bis zu 0,40 Gew.-%, insbesondere bis zu 0,3 Gew.-% und insbesondere mindestens 0,01 Gew.-% oder mindestens 0,02 Gew.-% V.The alloying fine adjustment with regard to the mechanical properties and the structure of a steel used according to the invention is carried out according to the alloy concept used according to the invention via a combined microalloy made up of the elements Boron ("B") in optional contents of up to 0.0025% by weight, in particular in contents of 0.0001-0.0025% by weight B or 0.0005-0.0025% by weight B, Nitrogen ("N") in contents of 0.004-0.020% by weight, in particular at least 0.006% by weight N or up to 0.0150% by weight N, aluminum ("AI") in contents of 0.004-0.020% by weight .-% and niobium ("Nb") in optional contents of up to 0.020% by weight, in particular up to 0.015% by weight and in particular at least 0.003% by weight or at least 0.005% by weight of Nb, titanium (" Ti ") in optional contents of up to 0.02% by weight or up to 0.015% by weight, in particular at least 0.001% by weight or at least 0.005% by weight Ti, and vanadium (" V ") in optional Contents of up to 0.40% by weight, in particular up to 0.3% by weight and in particular at least 0.01% by weight or at least 0.02% by weight of V.
Um die Vorteile der Anwesenheit der Mikrolegierungselemente und von Aluminium sicher zu nutzen, kann es zweckmäßig sein, den Al-Gehalt auf mindestens 0,005 Gew.-%, den Ti-Gehalt auf mindestens 0,001 Gew.-%, den V-Gehalt auf mindestens 0,02 Gew.-% oder den Nb-Gehalt auf mindestens 0,003 Gew.-% einzustellen. Dabei können die Mikrolegierungselemente V, Ti, Nb einerseits und Al andererseits jeweils in Kombination mit einem oder mehreren Elementen der Gruppe "Al, V, Ti, Nb" oder alleine in oberhalb der genannten Mindestgehalte liegenden Mengen vorhanden sein. Bei Gehalten von bis zu 0,01 Gew.-% Ti, von bis zu 0,1 Gew.-% Nb, von bis zu 0,075 Gew.-% V oder von bis zu 0,020 Gew.-% Al lassen sich die Wirkungen dieser Elemente im erfindungsgemäß verwendeten Stahl besonders wirksam nutzen. Auch hier können die genannten Obergrenzen der Gehalte an Ti, Nb, V oder Al jeweils alleine oder in Kombination miteinander eingehalten werden, um die jeweils optimale Wirkung des betreffenden Legierungselements zu erzielen.In order to safely use the advantages of the presence of the micro-alloy elements and of aluminum, it can be expedient to reduce the Al content to at least 0.005% by weight, the Ti content to at least 0.001% by weight, and the V content to at least 0 , 02% by weight or the Nb content to at least 0.003% by weight. The micro-alloy elements V, Ti, Nb on the one hand and Al on the other hand can be present in each case in combination with one or more elements from the group "Al, V, Ti, Nb" or alone in amounts above the minimum contents mentioned. At contents of up to 0.01 wt% Ti, up to 0.1 wt% Nb, up to 0.075 wt% V or up to 0.020 wt% Al, the effects of these can be exhibited Use elements in the steel used according to the invention particularly effectively. Here, too, the stated upper limits of the contents of Ti, Nb, V or Al can be adhered to either alone or in combination with one another in order to achieve the optimum effect of the respective alloying element.
Die Gehalte %AI, %Nb, %Ti, %V und %N an AI, Nb, Ti, V und N sind dabei im erfindungsgemäß zu verwendenden Stahl über die Bedingung 
Ebenso optional vorhandene Gehalte an Ni von bis zu 0,5 Gew.-% verbessern die Zähigkeit des erfindungsgemäß zu verwendenden Stahls. Falls dieser Effekt genutzt werden soll, tritt er ab einem Ni-Gehalt von mindestens 0,1 Gew.-%, insbesondere mindestens 0,15 Gew.-%, ein.Likewise, optionally present contents of Ni of up to 0.5% by weight improve the toughness of the steel to be used according to the invention. If this effect is to be used, it occurs from a Ni content of at least 0.1% by weight, in particular at least 0.15% by weight.
Zu den über das Ausgangsmaterial in den erfindungsgemäß zu verwendenden Stahl gelangenden oder gezielt zugegebenen Legierungselementen gehört auch Cu, dessen Gehalt zur Vermeidung von negativen Einflüssen im erfindungsgemäß zu verwendenden Stahl auf max. 0,3 Gew.-% begrenzt ist.The alloying elements that enter the steel to be used according to the invention via the starting material or are added in a targeted manner also include Cu, the content of which is limited to a maximum of 0.3% by weight in order to avoid negative influences in the steel to be used according to the invention.
Optional im erfindungsgemäß zu verwendenden Stahl vorhandenes Kobald ("Co") bewirkt in Gehalten von bis zu 1,5 Gew.-% eine Verschiebung der Bainitbildung zu kürzeren Zeiten. Der positive Einfluss von Co kann dabei insbesondere bei Co-Gehalten von mindestens 0,25 Gew.-%, insbesondere mindestens 0,5 Gew.-%, genutzt werden, wobei sich Co-Gehalte von bis zu 1,0 Gew.-% als besonders wirksam herausgestellt haben.Cobalt ("Co") optionally present in the steel to be used according to the invention, in contents of up to 1.5% by weight, causes the bainite formation to be shifted to shorter times. The positive influence of Co can be used in particular with Co contents of at least 0.25% by weight, in particular at least 0.5% by weight, with Co contents of up to 1.0% by weight have proven to be particularly effective.
Eine für die erfindungsgemäßen Zwecke besonders geeignete Stahllegierung besteht demnach entsprechend den voranstehenden Erläuterungen aus (in Gew.-%) 0,12 - 0,25 % C, 0,20 - 0,80 % Si, 0,40 - 1,20 % Mn, 1,0 - 3,0 % Cr, 0,5 - 1,8 % Mo, 0,004 - 0,020 % N, bis zu 0,40 % S, 0,004 - 0,020 % Al, 0,0005 - 0,0025 % B, bis zu 0,10 % Nb, bis zu 0,015 % Ti, bis zu 0,20 % V, bis zu 0,5 % Ni, und/oder bis zu 1,5 % Co, Rest Eisen und unvermeidbare Verunreinigungen, für die auch hier die oben bereits diesbezüglich gegebenen Erläuterungen gelten.A steel alloy particularly suitable for the purposes according to the invention accordingly consists of (in% by weight) 0.12 - 0.25% C, 0.20 - 0.80% Si, 0.40 - 1.20% Mn, 1.0-3.0% Cr, 0.5-1.8% Mo, 0.004-0.020% N, up to 0.40% S, 0.004-0.020% Al, 0.0005-0.0025% B, up to 0.10% Nb, up to 0.015% Ti, up to 0.20% V, up to 0.5% Ni, and / or up to 1.5% Co, the remainder being iron and unavoidable impurities, for which the explanations given above in this regard also apply here.
Grundsätzlich eignet sich der für die Herstellung von Stahlbauteilen zu verwendende Stahl für sämtliche der in den oben bereits genannten Merkblättern 452 und 477 beschriebenen thermochemischen Diffusionsverfahren "Carburieren" (Aufkohlen), "Carbonitrieren", "Nitrieren" oder "Nitrocarburieren".In principle, the steel to be used for the production of steel components is suitable for all of the thermochemical diffusion processes "carburizing", "carbonitriding", "nitriding" or "nitrocarburizing" described in the above mentioned leaflets 452 and 477.
Soweit ein Einsatzhärten durchgeführt werden soll, wird, wie im Merkblatt 452 im Einzelnen erläutert, zunächst als thermochemische Diffusionsbehandlung ein Carburieren oder Carbonitrieren durchgeführt. Nach der hierbei durch thermochemische Diffusion bewirkten Aufkohlung (Carburieren, Carbonitrieren) der Randschicht erfolgt beim konventionellen Einsatzhärten ein Härten gemäß den im Merkblatt 452 ebenfalls detailliert beschriebenen Härteverfahren "Direkthärten (Typ A)", "Einfachhärten (Typ B)", "Härten nach isothermischem Umwandeln (Typ C)" oder "Doppelhärten (Typ D)". Beim Direkthärten (Typ A) wird das Stahlbauteil direkt aus der Hitze der vorangegangen Carburierungs- oder Carbonitrierungsbehandlung abgeschreckt. Beim Einfachhärten (Typ B) wird das Stahlbauteil nach der vorangegangen Carburierungs- oder Carbonitrierungsbehandlung zunächst auf Raumtemperatur abgekühlt und anschließend erneut auf eine oberhalb der Ac1- und unterhalb der Ac3-Temperatur des Stahls liegende Austenitisierungstemperatur durcherwärmt und anschließend abgeschreckt. Beim Härten nach isothermischem Umwandeln (Typ C) wird das Stahlbauteil aus der Hitze der vorangegangen Carburierungs- oder Carbonitrierungsbehandlung zunächst bis zu einem Temperaturbereich abgekühlt, in dem sich bestimmte Carbidausscheidungen bilden, und anschließend ausgehend von diesem Temperaturbereich wieder auf eine oberhalb der Ac1- und unterhalb der Ac3- Temperatur des Stahls liegende Austenitisierungstemperatur durcherwärmt, um dann abgeschreckt zu werden. Beim Doppelhärten (Typ D) durchläuft das Stahlbauteil, nachdem es aus der Hitze der vorangegangen Carburierungs- oder Carbonitrierungsbehandlung wie beim Einfachhärten Typ A auf Raumtemperatur abgekühlt wurde, zweimal einen Härtevorgang, wie er beim Einfachhärten Typ A nur einmal absolviert wird.If case hardening is to be carried out, as explained in detail in leaflet 452, carburizing or carbonitriding is carried out as a thermochemical diffusion treatment. After the carburizing (carburizing, carbonitriding) of the surface layer brought about by thermochemical diffusion, hardening takes place during conventional case hardening in accordance with the hardening methods "direct hardening (type A)", "single hardening (type B)", "isothermal hardening", which are also described in detail in leaflet 452 Converting (Type C) "or" Double Hardening (Type D) ". With direct hardening (type A), the steel component is quenched directly from the heat of the preceding carburizing or carbonitriding treatment. With single hardening (type B), after the previous carburizing or carbonitriding treatment, the steel component is first cooled to room temperature and then heated again to an austenitizing temperature above the Ac1 and below the Ac3 temperature of the steel and then quenched. When hardening after isothermal conversion (type C), the steel component is initially cooled from the heat of the preceding carburizing or carbonitriding treatment to a temperature range in which certain carbide precipitates are formed, and then, starting from this temperature range, it is again heated through to an austenitizing temperature above the Ac1 and below the Ac3 temperature of the steel, in order then to be quenched. With double hardening (type D), after the steel component has been cooled to room temperature from the heat of the previous carburizing or carbonitriding treatment, as with single hardening type A, it goes through a hardening process twice, which is only performed once with single hardening type A.
Unabhängig davon, welches der vier hier genannten konventionellen Härteverfahren zur Anwendung kommt, sind bei der thermochemischen Diffusionsbehandlung und der anschließenden Härtung der aus erfindungsgemäß zu verwendendem Stahl bestehenden Stahlbauteile die durchzuführenden Abkühlungen in jedem Fall so einzustellen, dass sich einerseits in der durch das Carburieren oder Carbonitrieren aufgekohlten Randschicht härtesteigernde Ausscheidungen und im nicht aufgekohlten Kernbereich des Bauteils ein nach der oben erläuterten Maßgabe zu mindestens 80 Vol.-% aus Bainit bestehendes Gefüge einstellt. Hierzu ist bei der Abkühlung der Temperaturbereich von 800 - 500 °C jeweils in einer Zeit t8/5 von mindestens 6 s, insbesondere mindestens 10 s, und höchstens 600 s, zu durchlaufen.Regardless of which of the four conventional hardening processes mentioned here is used, in the thermochemical diffusion treatment and the subsequent hardening of the steel components made of steel to be used according to the invention, the cooling to be carried out must in any case be set so that, on the one hand, the carburizing or carbonitriding hardness-increasing precipitates on the carburized edge layer and, in the non-carburized core area of the component, a structure consisting of at least 80% by volume of bainite according to the stipulation explained above. For this purpose, the temperature range of 800-500 ° C. must be passed through in a time t8 / 5 of at least 6 s, in particular at least 10 s, and at most 600 s, during the cooling process.
Soll dagegen zwecks Ausbildung der gehärteten Randschicht die thermochemische Diffusionsbehandlung als Nitrieren oder Nitrocarburieren durchgeführt werden, was nicht unter die gegenwärtige Erfindung fällt, so kann dazu die im Merkblatt 477 detailliert beschriebene Vorgehensweise gewählt werden. Hierbei wird das Stahlbauteil nach einer Erwärmung auf eine oberhalb der Ac3-Temperatur des Stahls, aus dem das Stahlbauteil besteht, liegenden Austenitisierungstemperatur kontinuierlich so abgekühlt, dass der Temperaturbereich von 800 - 500 °C in einer Zeit t8/5 von mindestens 6 s, insbesondere mindestens 10 s, und höchstens 1000 s, insbesondere höchstens 200 s, durchlaufen wird, um im Bauteil ein nach der oben erläuterten Maßgabe zu mindestens 80 Vol.-% aus Bainit bestehendes Gefüge zu bilden. Anschließend erfolgt dann der Nitrier- oder Nitrocarburier-Schritt, bei dem das Stahlbauteil jeweils entsprechend den im Merkblatt 477 enthaltenen Hinweisen und Maßgaben unter einer stickstoff- oder einer stickstoff- und kohlenstoffhaltigen Atmosphäre bei einer unterhalb der Ac1-Temperatur des Stahls, aus dem das Stahlbauteil besteht, liegenden Temperatur gehalten und anschließend abgekühlt wird.If, on the other hand, the thermochemical diffusion treatment is to be carried out as nitriding or nitrocarburizing for the purpose of forming the hardened surface layer, which is not covered by the present invention, then the procedure described in detail in leaflet 477 can be selected. Here, after being heated to an austenitizing temperature above the Ac3 temperature of the steel from which the steel component is made, the steel component is continuously cooled so that the temperature range of 800 - 500 ° C in a time t8 / 5 of at least 6 s, in particular at least 10 s, and a maximum of 1000 s, in particular a maximum of 200 s, is run through in order to form in the component a structure consisting of at least 80% by volume of bainite in accordance with the stipulation explained above. This is followed by the nitriding or nitrocarburizing step, in which the steel component is placed in a nitrogen or nitrogen and carbon-containing atmosphere at a temperature below the Ac1 temperature of the steel from which the steel component is made, in accordance with the instructions and stipulations contained in leaflet 477 exists, the lying temperature is maintained and then cooled.
Erinfungsgemäß wird das Stahlbauteil einem Einsatzhärten unterzogen und wird dazu in einem Arbeitsschritt
- a) aus dem erfindungsgemäß zu verwendenden Stahl in konventioneller Weise zu einem Stahlbauteil, bei dem es sich um ein Zahnrad, eine Welle, eine Achse oder einen Werkzeughalter handelt, geformt. Anschließend wird in einem Arbeitsschritt
- b) das betreffende Stahlbauteil dann einsatzgehärtet, indem
b1) das Stahlbauteil zunächst in einem Aufkohlungsschritt über eine Dauer von 150 min bis 250 Stunden bei einer Temperatur von 900 -1050 °C unter einem Medium gehalten wird, das Kohlenstoff und optional zusätzlich Stickstoff enthält, um an dem Stahlbauteil eine carburierte oder carbonitrierte Randschicht mit einerDicke von 0,3 - 15 µm zu erzeugen, und anschließend an den Aufkohlungsschritt dann so schnell auf Raumtemperatur abgekühlt wird, dass bei der Abkühlung der Temperaturbereich von 800 - 500 °C innerhalb von 6 - 600 s durchlaufen wird. Hierzu geeignete Abkühlgeschwindigkeiten betragen typischerweise bis zu 5 K/s,insbesondere mindestens 0,5 K/s, wobei die Abkühlung im Temperaturbereich von 800 - 500 °C insbesondere mit mehr als 1,5 K/s absolviert wird.
- a) formed from the steel to be used according to the invention in a conventional manner to form a steel component which is a gearwheel, a shaft, an axle or a tool holder. Then in one step
- b) the steel component in question is then case-hardened by
b1) the steel component is initially held in a carburizing step for a period of 150 min to 250 hours at a temperature of 900-1050 ° C under a medium that contains carbon and optionally also nitrogen in order to have a carburized or carbonitrided surface layer on the steel component a thickness of 0.3 - 15 µm, and then the carburizing step is then cooled to room temperature so quickly that the temperature range of 800 - 500 ° C is passed through within 6 - 600 s during cooling. Cooling speeds suitable for this are typically up to 5 K / s, in particular at least 0.5 K / s, the cooling being completed in the temperature range from 800-500 ° C., in particular at more than 1.5 K / s.
Die Dauer, über die das Stahlbauteil während des Aufkohlungsschritts unter dem kohlenstoffhaltigen Medium gehalten wird, wird in an sich bekannter Weise in Abhängigkeit von der Größe des Bauteils sowie unter Berücksichtigung des jeweils eingesetzten kohlenstoffhaltigen Mediums und der Temperatur, bei der die Aufkohlung durchgeführt wird, so gewählt, dass eine aufgekohlte Randschicht mit einer innerhalb der erfindungsgemäßen Vorgaben liegenden Dicke erreicht wird. Die kürzeste Dauer kann dabei beispielsweise für kleinere Bauteile, wie Getriebeteile, insbesondere Zahnräder, Wellen und Achsen, von Automobilgetrieben und desgleichen, angezeigt sein, wogegen die längste Dauer bei großen Bauteilen, wie Getriebeteilen, insbesondere Zahnrädern, Wellen und Achsen, von Großgetrieben angemessen sein können, die für Großwälzlager bestimmt sind, wie sie in Windkraftanlagen oder Schiffsantrieben Verwendung finden.The duration for which the steel component is held under the carbonaceous medium during the carburizing step is set in a manner known per se, depending on the size of the component and taking into account the carbonaceous medium used and the temperature at which the carburization is carried out, as follows chosen so that a carburized surface layer with a thickness lying within the specifications according to the invention is achieved. The shortest duration can be indicated, for example, for smaller components, such as gear parts, in particular gears, shafts and axles, of automobile transmissions and the like, whereas the longest duration can be appropriate for large components, such as gear parts, in particular gears, shafts and axles, of large gears that are intended for slewing bearings such as those used in wind turbines or ship propulsion systems.
In der Praxis liegt die Temperatur, bei dem das Stahlbauteil während des Aufkohlungsschritts (Arbeitsschritt b.1) gehalten wird, typischerweise bei bis zu 950 °C. Durch die Wahl höherer Temperaturen kann der Aufkohlungsvorgang beschleunigt und dementsprechend die für die erforderliche Aufkohlung benötigte Dauer verkürzt werden.In practice, the temperature at which the steel component is kept during the carburizing step (step b.1) is typically up to 950 ° C. By choosing higher temperatures, the carburizing process can be accelerated and the duration required for the required carburizing can be shortened accordingly.
Nach dem Arbeitsschritt b1) wird das Stahlbauteil in einem Härteschritt
b2) auf eine Austenitisierungstemperatur erwärmt, die mindestens 20 °C oberhalb der Ac1-Temperatur und unterhalb der Ac3-Temperatur des Stahls liegt, aus dem das Stahlbauteil besteht, und ausgehend von der Austenitisierungstemperatur mit einer Abkühlgeschwindigkeit von 0,5 - 50 K/s, insbesondere mindestens 1,5 K/s oder mehr als 1,5 K/s, auf Raumtemperatur abgekühlt.After step b1) the steel component is hardened in a hardening step
b2) heated to an austenitizing temperature which is at least 20 ° C above the Ac1 temperature and below the Ac3 temperature of the steel from which the steel component is made, and based on the austenitizing temperature with a cooling rate of 0.5 - 50 K / s , in particular at least 1.5 K / s or more than 1.5 K / s, cooled to room temperature.
Um nach der thermochemischen Diffusionsbehandlung (Arbeitsschritt b1) möglicherweise im Bauteil vorhandene Spannungen abzubauen, kann das aus erfindungsgemäß verwendetem Stahl bestehende Stahlbauteil zwischen den Arbeitsschritten b1) und b2) optional einem Spannungsarmglühen unterzogen werden, bei dem es über eine Dauer von 15 - 120 min im Bereich von 150 - 680 °C gehalten wird.In order to relieve any stresses that may be present in the component after the thermochemical diffusion treatment (step b1), the steel component made of steel according to the invention can optionally be subjected to a stress-relieving anneal between steps b1) and b2), in which it is heated for a period of 15 - 120 min Range of 150 - 680 ° C is maintained.
Ebenso optional kann das Stahlbauteil nach dem Härten (Arbeitsschritt b2) optional in an sich bekannter Weise einer Anlassbehandlung unterzogen werden, bei der es über eine Dauer von 30 - 180 min bei einer Temperatur von 150 - 275 °C gehalten und anschließend ungesteuert auf Raumtemperatur abgekühlt wird. Durch ein solches Anlassen kann das Risiko von Rissbildung weiter reduziert werden.Also optionally, after hardening (step b2), the steel component can optionally be subjected to a tempering treatment in a manner known per se, in which it is kept at a temperature of 150-275 ° C for a period of 30-180 minutes and then cooled to room temperature in an uncontrolled manner becomes. Such tempering can further reduce the risk of cracking.
Insbesondere durch Anwendung des voranstehend erläuterten Verfahrens kann ein erfindungsgemäßes einsatzgehärtetes Stahlbauteil erzeugt werden, dass aus dem erfindungsgemäß zu verwendenden Stahl, der aus (in Gew.-%) 0,12 - 0,25 % C, 0,20 - 0,80 % Si, 0,40 - 1,20 % Mn, 1,0 - 3,0 % Cr, 0,5 - 1,8 % Mo, 0,004 - 0,020 % N, bis zu 0,40 % S, 0,004 - 0,020 % AI, 0,0001 - 0,0025 % B, bis zu 0,10 % Nb, bis zu 0,01 % Ti, bis zu 0,20 % V, bis zu 0,5 % Ni, bis zu 1,0 % Co und als aus Rest Eisen und unvermeidbaren Verunreinigungen besteht, hergestellt ist und eine Randschicht mit einer Härte von 500 - 800 HV aufweist sowie erfindungsgemäß in seinem Kernbereich zu mindestens 80 Vol.-% aus Bainit besteht, der aus hoch angelassenem Bainit, welcher aus dem Gefüge stammt, das das Stahlbauteil nach dem Einsetzen (Arbeitsschritt b.1) und vor dem Härten (Arbeitsschritt b.2) aufwies, und neu gebildetem Bainit sowie zu höchstens 20 Vol.-% aus Restaustenit, Ferrit, Perlit oder Martensit zusammengesetzt ist.In particular by using the method explained above, a case-hardened steel component according to the invention can be produced that is made from the steel to be used according to the invention, which consists of (in% by weight) 0.12-0.25% C, 0.20-0.80% Si, 0.40-1.20% Mn, 1.0-3.0% Cr, 0.5-1.8% Mo, 0.004-0.020% N, up to 0.40% S, 0.004-0.020% AI, 0.0001 - 0.0025% B, up to 0.10% Nb, up to 0.01% Ti, up to 0.20% V, up to 0.5% Ni, up to 1.0% Co and as the remainder iron and unavoidable impurities, is made and a surface layer with a hardness of 500 - 800 HV and according to the invention in its core area consists of at least 80% by volume of bainite, which consists of highly tempered bainite, which comes from the structure that the steel component after insertion (step b.1) and before hardening (step b.2 ), and newly formed bainite and a maximum of 20% by volume of retained austenite, ferrite, pearlite or martensite.
Diese Gefügezusammensetzung entsteht durch eine Härtung der erfindungsgemäßen Bauteile im Zweiphasengebiet. Dabei können die aus "alten", also vor dem Härten (Arbeitsschritt b.2) entstandenen bestehenden bainitischen Gefügeanteile von den aus "neuen", im Zuge des Härtens entstandenen und hoch angelassenen bainitischen Gefügeanteilen durch eine leichte Braunfärbung des neuen Bainits von dem alten, hoch angelassenen Bainit unterschieden werden, der eine gräuliche Färbung und eine angedeutet körnige Struktur besitzt.This structural composition results from hardening of the components according to the invention in the two-phase area. The existing bainitic structural components that have arisen from the "old", i.e. prior to hardening (step b.2), can be separated from the "new" bainitic structural components that have arisen in the course of the hardening by a slight brown coloration of the new bainite from the old, A distinction can be made between highly tempered bainite, which has a grayish color and an indicated grainy structure.
Dabei zeichnet sich das Gefüge eines Bauteils, das das voranstehend erläuterte, nach Maßgabe der Erfindung modifizierte Einsatzhärtverfahren durchlaufen hat, dadurch aus, dass es im Kernbereich des Stahlbauteils eine gemäß DIN EN 10045 bestimmte Charpy-V Kerbschlagarbeit von mehr als 40 J, insbesondere mehr als 60 J, aufweist.The structure of a component that has gone through the above-explained case hardening process modified in accordance with the invention is characterized in that it has a Charpy-V notch impact energy of more than 40 J, in particular more than 40 J, determined in accordance with DIN EN 10045, in the core area of the steel component 60 J.
Soll die gehärtete Randschicht durch Nitrieren oder Nitrocarburieren erzeugt werden, was nicht unter die gegenwärtige Erfindung fällt, so kann die dazu erforderliche thermochemische Diffusionsbehandlung insbesondere ausgehend von der optimierten Zusammensetzung des erfindungsgemäß zu verwendenden Stahls mit (in Gew.-%) 0,12 - 0,25 % C, 0,20 - 0,80 % Si, 0,40 - 1,20 % Mn, 1,0 - 3,0 % Cr, 0,5 - 1,8 % Mo, 0,004 - 0,020 % N, bis zu 0,40 % S, 0,004 - 0,020 % AI, 0,0005 - 0,0025 % B, bis zu 0,10 % Nb, bis zu 0,01 % Ti, bis zu 0,20 % V oder bis zu 0,5 % Ni, sowie bis zu 1,5 % Co, Rest Eisen und unvermeidbaren Verunreinigungen, wie folgt durchgeführt werden:
- A) Aus dem Stahl wird ein Stahlbauteil geformt.
- B) Das Stahlbauteil wird einer Nitrier- oder Nitrocarburier-Behandlung unterzogen, bei der
- B.1) das Stahlbauteil zunächst über eine Austenitisierungsdauer von 15 - 120 min auf eine Austenitsierungsstemperatur, die mindestens 20 °C, insbesondere 20 -100 °C oder 30 - 50 °C, oberhalb der Ac3-Temperatur des Stahls liegt, aus dem das Stahlbauteil besteht, durcherwärmt und anschließend so schnell auf Raumtemperatur abgekühlt wird, dass bei der Abkühlung der Temperaturbereich von 800 - 500 °C innerhalb von weniger als 200 s durchlaufen wird, um ein zu mindestens 80 Vol.-% bestehendes Gefüge im Bauteil zu erzeugen,
und - B.2) das Stahlbauteil anschließend für das Nitrieren oder Nitrocarburieren über eine Dauer von 60
min bis 100 Stunden unter einer stickstoff- oder stickstoff- und kohlenstoffhaltigen Atmosphäre, bei einer unterhalb der Ac1-Temperatur des Stahls, aus dem das Stahlbauteil besteht, liegenden, typischerweise 440 - 580 °C betragenden Temperatur gehalten und anschließend abgekühlt wird, um an dem Stahlbauteil eine gehärtete Randschicht mit einer Dicke von 1 - 1200 µm zu erzeugen.
- B.1) das Stahlbauteil zunächst über eine Austenitisierungsdauer von 15 - 120 min auf eine Austenitsierungsstemperatur, die mindestens 20 °C, insbesondere 20 -100 °C oder 30 - 50 °C, oberhalb der Ac3-Temperatur des Stahls liegt, aus dem das Stahlbauteil besteht, durcherwärmt und anschließend so schnell auf Raumtemperatur abgekühlt wird, dass bei der Abkühlung der Temperaturbereich von 800 - 500 °C innerhalb von weniger als 200 s durchlaufen wird, um ein zu mindestens 80 Vol.-% bestehendes Gefüge im Bauteil zu erzeugen,
- A) A steel component is formed from the steel.
- B) The steel component is subjected to a nitriding or nitrocarburizing treatment in which
- B.1) the steel component initially over an austenitizing period of 15-120 minutes to an austenitizing temperature that is at least 20 ° C, in particular 20-100 ° C or 30-50 ° C, above the Ac3 temperature of the steel from which the Steel component consists, is heated through and then cooled to room temperature so quickly that the temperature range of 800 - 500 ° C is passed through within less than 200 s during cooling in order to create a structure in the component that is at least 80% by volume,
and - B.2) the steel component is then nitrided or nitrocarburized for a period of 60 min to 100 hours in a nitrogen or nitrogen and carbon-containing atmosphere at a temperature below the Ac1 temperature of the steel of which the steel component is made, typically 440-580 ° C temperature is maintained and then cooled in order to produce a hardened surface layer with a thickness of 1-1200 µm on the steel component.
- B.1) the steel component initially over an austenitizing period of 15-120 minutes to an austenitizing temperature that is at least 20 ° C, in particular 20-100 ° C or 30-50 ° C, above the Ac3 temperature of the steel from which the Steel component consists, is heated through and then cooled to room temperature so quickly that the temperature range of 800 - 500 ° C is passed through within less than 200 s during cooling in order to create a structure in the component that is at least 80% by volume,
Beim in der voranstehend angegebenen Weise durchgeführten Nitrieren oder Nitrocarburieren entstehen aus den verwendeten Stahl nach Maßgabe der Erfindung vorhandene Gehalte an Cr, V, Nb oder Ti durch die Bildung von Nitriden für eine hohe Oberflächenhärte. Der bainitische Kernbereich (Matrix) erfährt beim Nitrieren oder Nitrocarborieren eine Härtesteigerung um ca. 100 - 150 MPa durch die Entstehung von Sonderkarbiden insbesondere aus den im Stahl enthaltenen Gehalten an Mo (molybdänreiches Karbid).In the nitriding or nitrocarburizing carried out in the manner indicated above, Cr, V, Nb or Ti contents of the steel used in accordance with the invention arise from the formation of nitrides for a high surface hardness. The bainitic core area (matrix) experiences an increase in hardness of approx. 100 - 150 MPa during nitriding or nitrocarboring due to the formation of Special carbides, in particular from the Mo content (molybdenum-rich carbide) contained in the steel.
Die jeweils konkret eingestellten Parameter "Dauer" und "Temperatur" der Nitrier- oder Nitrocarburier-Behandlung werden dabei in an sich bekannter Weise in Abhängigkeit von der Bauteilgröße so eingestellt, dass eine gehärtete Randschicht mit einer innerhalb der erfindungsgemäßen Vorgaben liegenden Dicke erzielt wird.The specifically set parameters "duration" and "temperature" of the nitriding or nitrocarburizing treatment are set in a manner known per se, depending on the component size, so that a hardened surface layer is achieved with a thickness within the specifications according to the invention.
Soll eine spanabhebende Bearbeitung des Bauteils durchgeführt werden, um beispielsweise seine Maßhaltigkeit zu optimieren, so wird diese vorteilhafterweise zwischen den Arbeitsschritten B1) und B2) am nach dem Arbeitsschritt B1) noch relativ weichen Stahlbauteil durchgeführt, um den Werkzeugverschleiß gegenüber einer Zerspanung im endgehärteten Zustand zu vermindern.If machining of the component is to be carried out, for example to optimize its dimensional accuracy, this is advantageously carried out between steps B1) and B2) on the steel component, which is still relatively soft after step B1), in order to reduce tool wear compared to machining in the final hardened state Reduce.
Der erfindungsgemäß zu verwendende Stahl ist besonders zur Herstellung von randschichtgehärteten Zahnrädern, Achsen, Wellen oder Werkzeughalter für pulvermetallurgisch hergestellte Schneidwerkzeuge geeignet.The steel to be used according to the invention is particularly suitable for the production of surface-hardened gear wheels, axles, shafts or tool holders for cutting tools produced by powder metallurgy.
Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen erläutert.The invention is explained below on the basis of exemplary embodiments.
Es sind drei erfindungsgemäß zu verwende Schmelzen S1, S2, S3 erschmolzen worden, deren Zusammensetzung in Tabelle 1 angegeben ist.Three melts S1, S2, S3 to be used according to the invention have been melted, the composition of which is given in Table 1.
In einem ersten Versuch ist aus dem Stahl S1 ein Zahnrad geformt worden. Das Zahnrad ist anschließend einem in konventioneller Weise nach Maßgabe der im Merkblatt 452 beschriebenen Vorgehensweise zunächst einem Aufkohlen bei 920 °C über eine Dauer von 300 min unter einer in an sich für diesen Zweck bekannten Weise zusammengesetzten kohlenstoffhaltigen Atmosphäre unterzogen worden. Auf diese Weise ist an dem Zahnrad durch thermochemische Diffusion eine aufgekohlte (carburierte) Randschicht mit einer Dicke von 520 µm entstanden. Anschließend ist das Zahnrad auf Raumtemperatur abgekühlt worden, wobei die Abkühlrate 2 K/s betrug und der kritische Temperaturbereich von 800 - 500 °C in einer t8/5-Zeit von 10 min durchlaufen worden ist.In a first attempt, a gear was formed from steel S1. The gear was then subjected to a conventional manner in accordance with the procedure described in leaflet 452, initially to carburizing at 920 ° C. over a period of 300 min under a carbon-containing atmosphere composed in a manner known per se for this purpose. In this way the gear is through thermochemical diffusion created a carburized surface layer with a thickness of 520 µm. The gearwheel was then cooled to room temperature, the cooling rate being 2 K / s and the critical temperature range of 800-500 ° C. being passed through in a t8 / 5 time of 10 minutes.
Das erhaltene Zahnrad ist daraufhin auf eine 920 °C betragende Austenitisierungstemperatur erwärmt und bei dieser Temperatur für 30 min gehalten worden. Anschließend ist das Zahnrad mit einer Abkühlgeschwindigkeit von 2 K/s abgeschreckt worden. Dabei ist der kritische Temperaturbereich von 800 - 500 °C in einer t8/5-Zeit von 600 s durchlaufen worden.The resulting gear was then heated to an austenitizing temperature of 920 ° C. and held at this temperature for 30 minutes. The gear was then quenched at a cooling rate of 2 K / s. The critical temperature range of 800 - 500 ° C was passed through in a t8 / 5 time of 600 s.
Das derart einsatzgehärtete Zahnrad wies an der Oberfläche seiner gehärteten Randschicht eine Härte von 750 HV und in seinem die gehärtete Randschicht tragenden Kernbereich (Matrix) ein vollständig bainitisches Gefüge auf. Die Kerbschlagarbeit Charpy-V des ungehärteten Kernbereichs des Zahnrads betrug im Mittel von drei Proben 106 J.The gear wheel case-hardened in this way had a hardness of 750 HV on the surface of its hardened edge layer and a completely bainitic structure in its core area (matrix) bearing the hardened edge layer. The Charpy-V notched impact work of the unhardened core area of the gear averaged 106 J.
In einem zweiten Versuch ist aus dem Stahl S2 wiederum ein Zahnrad geformt worden. Das Zahnrad ist anschließend zunächst einem Aufkohlen bei 920 °C über eine Dauer von 30 min unter einer für diesen Zweck im Stand der Technik üblichen kohlenstoffhaltigen Atmosphäre unterzogen worden. Auf diese Weise ist an dem Zahnrad durch thermochemische Diffusion eine aufgekohlte (carburierte) Randschicht mit einer Dicke von 535 µm entstanden.In a second experiment, a gear was again formed from the steel S2. The gear wheel was then first subjected to carburizing at 920 ° C. over a period of 30 minutes under a carbon-containing atmosphere customary for this purpose in the prior art. In this way, a carbonized (carburized) surface layer with a thickness of 535 µm was created on the gearwheel by thermochemical diffusion.
Anschließend ist das Zahnrad in Öl auf Raumtemperatur abgeschreckt worden. Der kritische Temperaturbereich von 800 - 500 °C ist dabei in einer t8/5-Zeit von 17 s durchlaufen worden.The gear was then quenched in oil to room temperature. The critical temperature range of 800 - 500 ° C was passed through in a t8 / 5 time of 17 s.
Daraufhin hat das Zahnrad ein Spannungsarmglühen durchlaufen, bei dem es für eine Stunde bei 650 °C gehalten worden ist, um bei der zuvor absolvierten Aufkohlungsbehandlung entstandene Spannungen abzubauen.The gearwheel then went through a stress-relieving heat treatment, in which it was held at 650 ° C. for one hour in order to relieve the stresses that had arisen during the previously performed carburizing treatment.
Nach dem Spannungsarmglühen ist das Bauteil in einem Härteschritt auf eine Austenitisierungstemperatur erwärmt und bei dieser Temperatur für eine Stunde gehalten worden, die 40 °C unterhalb der Ac3-Temperatur des Stahls S2 lag, wobei die Ac3-Temperatur des Stahls S2 zuvor in an sich bekannter Weise mittels eines Dilatometerversuchs bestimmt worden ist. Anschließend ist das Zahnrad wiederum in Öl abgeschreckt worden, so dass auch hier die t8/5-Zeit 17 s betrug.After the stress relief annealing, the component was heated in a hardening step to an austenitizing temperature and held at this temperature for one hour, which was 40 ° C. below the Ac3 temperature of steel S2, the Ac3 temperature of steel S2 previously known per se Way has been determined by means of a dilatometer experiment. The gearwheel was then quenched in oil again, so that here too the t8 / 5 time was 17 s.
Nach dem Härten ist das Zahnrad einem konventionellen Anlassen unterzogen worden, bei dem es über eine Stunde bei 180 °C gehalten worden ist.After hardening, the gear was subjected to a conventional tempering in which it was held at 180 ° C. for one hour.
Das derart einsatzgehärtete Zahnrad wies an der Oberfläche seiner gehärteten Randschicht eine Härte von 750 HV und in seinem die gehärtete Randschicht tragenden Kernbereich (Matrix) ein vollständig bainitisches Gefüge auf, das aus neu gebildetem und altem hoch angelassenen Bainit bestand. Die Kerbschlagarbeit Charpy-V betrug bei drei Proben im Mittel 62 J.The case-hardened gear wheel had a hardness of 750 HV on the surface of its hardened edge layer and a completely bainitic structure in its core area (matrix) bearing the hardened edge layer, which consisted of newly formed and old, highly tempered bainite. The Charpy-V impact work averaged 62 years for three samples.
In einem dritten Versuch ist aus dem Stahl S3 ein Zahnrad mit einem Durchmesser von weniger als 40 mm geformt worden. Das Zahnrad ist anschließend zunächst einem Aufkohlen bei 920 °C über eine Dauer von 30 min unter einer zu diesem Zweck üblicherweise eingesetzten kohlenstoffhaltigen Atmosphäre unterzogen worden. Auf diese Weise ist an dem Zahnrad durch thermochemische Diffusion eine aufgekohlte (carburierte) Randschicht mit einer Dicke von 530 µm entstanden. Anschließend ist das Zahnrad mit einer Abkühlgeschwindigkeit von 3 K/s auf Raumtemperatur in Wasser abgeschreckt worden. Der kritische Temperaturbereich von 800 - 500 °C ist dabei in einer t8/5-Zeit von 300 s durchlaufen worden.In a third experiment, a gear with a diameter of less than 40 mm was formed from steel S3. The gearwheel was then first subjected to carburizing at 920 ° C. over a period of 30 minutes under a carbon-containing atmosphere that is usually used for this purpose. In this way, a carbonized (carburized) surface layer with a thickness of 530 µm was created on the gear wheel by thermochemical diffusion. The gear was then quenched in water at a cooling rate of 3 K / s to room temperature. The critical temperature range of 800 - 500 ° C was passed through in a t8 / 5 time of 300 s.
Nach dieser Aufkohlungsbehandlung ist das Bauteil in einem Härteschritt auf eine Austenitisierungstemperatur erwärmt und bei dieser Temperatur für eine Stunde gehalten worden, die 920 °C betrug. Anschließend ist das Zahnrad in Wasser abgeschreckt worden, wobei hier die t8/5-Zeit 300 s betrug.After this carburizing treatment, the component was heated in a hardening step to an austenitizing temperature and held at this temperature for one hour, which was 920.degree. The gearwheel was then quenched in water, the t8 / 5 time being 300 s.
Das derart einsatzgehärtete Zahnrad wies an der Oberfläche seiner gehärteten Randschicht eine Härte von 760 HV und in seinem die gehärtete Randschicht tragenden Kernbereich (Matrix) ein vollständig bainitisches Gefüge auf. Die Kerbschlagarbeit Charpy-V betrug bei drei Proben im Mittel 78 J.The gear wheel case-hardened in this way had a hardness of 760 HV on the surface of its hardened edge layer and a completely bainitic structure in its core area (matrix) bearing the hardened edge layer. The Charpy-V impact work averaged 78 years for three specimens.
Mit dem dritten Versuch konnte somit gezeigt werden, dass durch die Zugabe wirksamer Gehalte an Co der Gefahr begegnet werden kann, dass es bei aus erfindungsgemäß legierten Stahlbauteilen mit kleinen Durchmessern von in der Regel weniger als 40 mm und einer schroffen Abkühlung in Wasser auch bei grundsätzlich bainitisch umwandelnden Stählen zu einer unerwünschten martensitischen Umwandlung der äußeren Schale kommt. Die Zone martensitischer Umwandlung kann ohne geeignete Gegenmaßnahmen mehrere Millimeter dick sein und ist vor allem bei einer mechanischen Bearbeitung störend. Durch den Zusatz von Kobalt kann der Beginn der bainitischen Umwandlung beschleunigt werden, wie anhand des in
Claims (5)
- Method for producing a case-hardened steel component, namely a gear wheel, a shaft, an axle or a tool holder, in the case of which the steel componenta) is shaped from a steel, which consists of in % by weight
C: 0.1 - 0.30%, Si: 0 - 0.80%, Mn: 0.20 - 2.00%, Cr: 0 - 4.00%, Mo: 0.5 - 1.80%, N: 0.004 - 0.020%, S: 0 - 0.40%, Al: 0.004 - 0.020%, B: 0 - 0.0025% Nb: 0 - 0.20%, Ti: 0 - 0.02%, V: 0 - 0.40%, Ni: 0 - 0.5%, Cu: 0 - 0.3%, Co: 0 - 1.5%
wherein the Al content %AI, the Nb content %Nb, the Ti content %Ti, the V content %V and the N content %N of the steel meet the following condition:
b) the steel component in question is case-hardened bysuch that the obtained steel component has a thermochemically hardened edge layer and in its core region a structure, which is composed by at least 80% by volume of bainite, which consists of highly-tempered bainite originating from the structure, which the steel component comprised after case hardening (work step b.1) and before the hardening (work step b.2), and newly formed bainite and up to at most 20% by volume of residual austenite, ferrite, perlite or martensite.b1) the steel component being held in a carburisation step for a duration of 150 min to 250 hours, at a temperature of 900 - 1050°C under a medium which contains carbon and optionally additionally nitrogen in order to produce a carburised or carbonitrided edge layer with a thickness of 0.3 - 15 µm on the steel component and after the carburisation step quickly being cooled to room temperature such that in the case of cooling the temperature range of 800 - 500°C is passed through within 6 - 600 seconds
andb2) the steel component, in a hardening step completed after the carburisation step (work step b1), being heated to an austenitisation temperature which is at least 20°C above the Ac1 temperature and below the Ac3 temperature of the steel, of which the steel component consists, and proceeding from the austenitisation temperature being cooled at a cooling speed of 0.5 - 50 K/s to room temperature - Method according to claim 1, characterised in that the steel (in % by weight) contains 0.12 - 0.25% C, 0.20 - 0.80% Si, 0.40 - 1.20% Mn, 1.0 - 3.0% Cr, 0.5 - 1.8% Mo, 0.004 - 0.020% N, up to 0.40% S, 0.004 - 0.020% Al, 0.0001 - 0.0025% B, up to 0.10% Nb, up to 0.015% Ti, up to 0.20% V, up to 0.5% Ni and/or up to 1.0% Co.
- Method according to claim 1 or 2, characterised in that the steel component between the works steps b1) and b2) is optionally subjected to a stress relief heat treatment at a temperature of 150 - 680°C for a duration of 15 - 120 min.
- Method according to any one of the preceding claims, characterised in that the steel component is optionally subjected to a tempering treatment after the hardening (work step b2), in which case it is held for a duration of 30 - 180 min at a temperature of 150 - 275°C and then cooled in an uncontrolled manner to room temperature.
- Method according to any one of the preceding claims, characterised in that the structure in the core region of the steel component has a Charpy-V notch impact strength of more than 40 J, which is determined according to DIN EN 10045.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PT181820242T PT3591081T (en) | 2018-07-05 | 2018-07-05 | Use of a steel for producing a steel component, namely for a gearwheel, a shaft, an axle or a tool holder to a thermochemically cured edge layer and such steel component having a thermochemically cured edge layer |
| ES18182024T ES2878652T3 (en) | 2018-07-05 | 2018-07-05 | Procedure for the fabrication of a case-hardened steel construction part |
| EP18182024.2A EP3591081B1 (en) | 2018-07-05 | 2018-07-05 | Method for producing a case-hardened steel component |
| PL18182024T PL3591081T3 (en) | 2018-07-05 | 2018-07-05 | Method for producing a case-hardened steel component |
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| EP18182024.2A EP3591081B1 (en) | 2018-07-05 | 2018-07-05 | Method for producing a case-hardened steel component |
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| EP3591081B1 true EP3591081B1 (en) | 2021-04-07 |
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| EP (1) | EP3591081B1 (en) |
| ES (1) | ES2878652T3 (en) |
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| EP3878985A1 (en) * | 2020-03-09 | 2021-09-15 | Areospace Trasmission Technologies GmbH | Method and device for manufacturing heat-treated workpieces, in particular helical gear wheels |
| CN113652611A (en) * | 2021-08-17 | 2021-11-16 | 山西太钢不锈钢股份有限公司 | High-speed rail gear steel and preparation method thereof |
| CN114410947B (en) * | 2022-01-26 | 2024-01-16 | 马鞍山钢铁股份有限公司 | Efficient heat treatment process for carburized driven gear blank for railway locomotive |
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| JP4022607B2 (en) * | 1999-07-21 | 2007-12-19 | 日産自動車株式会社 | Manufacturing method of high surface pressure resistant member |
| JP2006169637A (en) * | 2001-05-14 | 2006-06-29 | Sanyo Special Steel Co Ltd | Method for manufacturing high-strength carburized part |
| JP2006291310A (en) * | 2005-04-12 | 2006-10-26 | Daido Steel Co Ltd | Crankshaft and producing method therefor |
| JP5123335B2 (en) * | 2010-01-28 | 2013-01-23 | 本田技研工業株式会社 | Crankshaft and manufacturing method thereof |
| EP2578717B1 (en) * | 2010-11-17 | 2015-09-16 | Nippon Steel & Sumitomo Metal Corporation | Steel for nitriding purposes, and nitrided member |
| PT3168312T (en) | 2015-11-16 | 2019-07-16 | Deutsche Edelstahlwerke Specialty Steel Gmbh & Co Kg | Engineering steel with bainitic structure, forged part produced therefrom and method for making a forged part |
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