WO2011114836A1 - 表層硬化処理用鋼及び表層硬化鋼部品とその製造方法 - Google Patents
表層硬化処理用鋼及び表層硬化鋼部品とその製造方法 Download PDFInfo
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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
- C21D9/32—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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- 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
- C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—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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- C—CHEMISTRY; METALLURGY
- 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
- C23C8/08—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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- C—CHEMISTRY; METALLURGY
- 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
- C23C8/28—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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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16G—BELTS, CABLES, OR ROPES, PREDOMINANTLY USED FOR DRIVING PURPOSES; CHAINS; FITTINGS PREDOMINANTLY USED THEREFOR
- F16G5/00—V-belts, i.e. belts of tapered cross-section
- F16G5/16—V-belts, i.e. belts of tapered cross-section consisting of several parts
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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
- C21D2211/004—Dispersions; Precipitations
Definitions
- the present invention relates to a surface hardening steel, a surface hardening steel part, and a manufacturing method thereof.
- Power transmission parts for example, gears, bearings, CVT sheaves, shafts, etc.
- a surface hardening treatment for example, carburizing treatment is superior to other surface hardening treatments in terms of surface hardness, depth of hardened layer, productivity, etc. Many.
- medium carbon alloy steel such as SCM420, SCR420, SNCM220 defined in JISG4053, hot forging, cold forging, cutting, or a combination thereof
- Machining is performed so as to obtain a predetermined shape, and then carburizing or carbonitriding is performed.
- Fatigue failure of carburized gears is broadly divided into bending fatigue (tooth root fatigue) and tooth surface fatigue (pitching, etc.).
- bending fatigue strength can be improved by improving the structure of the surface layer (reducing the grain boundary oxide layer and incompletely quenched layer), and can be greatly improved by applying shot peening. ing.
- the tooth surface fatigue strength can hardly be improved even by shot peening, so that the improvement of the tooth surface fatigue strength has been an issue. Further, since not only gears but also CVT sheaves and bearings are required to have higher surface pressure, there is a strong demand for improvement in surface fatigue such as tooth surface fatigue and rolling fatigue.
- a “high carbon carburizing (also called high concentration carburizing) technique” in which cementite is actively precipitated on the surface of carburized parts has been proposed.
- the carbon potential (hereinafter also referred to as CP) of the atmosphere is set to about 0.70 to 0.90%, and the carbon content of the surface layer part of the part is controlled to about 0.80%. Then, it is the process which makes the structure
- cementite is deposited and dispersed in the surface layer portion, and finally, a structure in which cementite is dispersed in martensite is obtained.
- Such a technique is also referred to as CD carburization: carbide dispersion carburizing.
- Carbon potential is a term indicating the carburizing ability of the atmosphere in which steel is heated.
- the basic definition of the carbon potential is “the carbon concentration of the steel surface when the steel is heated and carburized to a specific temperature in a gas atmosphere and reaches equilibrium with the gas atmosphere”.
- the carbon potential means the virtual carbon surface concentration at which cementite precipitation does not occur. Become. In this case, the carbon potential does not always coincide with the carbon solid solution concentration on the actual steel surface.
- high carbon carburizing is performed at a relatively high temperature (primary carburizing), and then cooled to near room temperature at a sufficiently high cooling rate so as not to form proeutectoid cementite. Then, it heats again, performs the precipitation process of the carbide
- Patent Document 1 proposes a method of performing secondary quenching by induction quenching.
- Patent Document 2 proposes a method of finely dispersing carbide by defining a heating pattern for secondary quenching.
- the secondary quenching not only increases the heat treatment cost, but also deteriorates the component performance. That is, by repeating the heat treatment, deformation caused by the heat treatment accumulates, the deformation of the parts inevitably increases, and the dimensional accuracy deteriorates.
- Patent Document 3 and Patent Document 4 the surface carbon concentration at the time of carburizing treatment is defined, carburizing treatment is performed in a temperature range calculated by an equation defined from chemical components, and carburizing treatment temperature and A method of manufacturing a high surface pressure resistant member having a required relationship and performing diffusion treatment at high temperature has been proposed.
- the diffusion treatment is performed at a temperature higher than the carburizing temperature, the coarsening of the carbide is caused, which is insufficient as an alternative treatment for the secondary quenching.
- the processing pattern shown as an invention of the embodiment of these references are quenched below 1 point A steel during carburizing. This is substantially the same process as the secondary quenching, and this method cannot avoid the deterioration of the dimensional accuracy of the parts.
- the present invention provides a steel for surface layer hardening treatment and a surface hardening steel capable of obtaining a part having high tooth surface fatigue strength and avoiding an increase in heat treatment deformation (deterioration of dimensional accuracy of the part) due to secondary quenching.
- An object is to provide a component and a method for manufacturing the component.
- the high carbon carburizing process is defined as “a carburizing process in which the CP is 0.90% or more at a time of 50% or more of the total carburizing process time”.
- high carbon gas carbonitriding treatment is performed on the surface somewhere in the carburizing treatment process in which CP is 0.90% or more in a time of 50% or more of the total carburizing treatment time.
- a process including an additional step of containing nitrogen is defined.
- a steel material containing 2.00 to 5.00% Cr by mass is subjected to high carbon gas carburizing or high carbon gas carbonitriding in a temperature range of 800 to 900 ° C.
- (Cr, Fe) 23 C 6 and / or (Cr, Fe) 3 C are precipitated on the surface layer during the carburizing process, and these precipitates are used as precipitation nuclei for cementite.
- a structure in which carbides (cementite and (Cr, Fe) 23 C 6 and / or (Cr, Fe) 3 C) are finely dispersed on the surface of the component is obtained by one heat treatment.
- the gist of the present invention is as follows.
- the steel for surface layer hardening treatment is a steel for surface layer hardening treatment that is carburized in a temperature range of 800 to 900 ° C., the chemical composition is in mass%, and C: 0.00. 10 to 0.60%, Si: 0.01 to 2.50%, Mn: 0.20 to 2.00%, S: 0.0001 to 0.10%, Cr: 2.00 to 5.00% Al: 0.001 to 0.50%, N: 0.0020 to 0.020%, P: 0.001 to 0.050%, and O: 0.0001 to 0.0030%.
- the balance consists of Fe and inevitable impurities, and the total content of Cr, Si and Mn satisfies 2.0 ⁇ Cr + Si + Mn ⁇ 8.0 by mass%.
- the chemical component is further in mass%, Ca: 0.0005 to 0.0030%, Mg: 0.0005 to 0.0030%, Zr: One or more of 0.0005 to 0.0030% may be contained.
- the chemical component is further in mass%, Mo: 0.01 to 1.00%, B: 0.0005 to 0.0050. %, Cu: 0.05 to 1.00%, and Ni: 0.05 to 2.00% may be contained.
- the chemical component is further in mass%, V: 0.005 to 0.50%, Nb: 0.005 to One or more of 0.10% and Ti: 0.005 to 0.50% may be contained.
- a steel part according to another aspect of the present invention is a steel part that has been subjected to carburizing treatment or carbonitriding treatment, and the component of the steel in the non-carburized portion of the steel part is C%. : 0.10 to 0.60%, Si: 0.01 to 2.50%, Mn: 0.20 to 2.00%, S: 0.0001 to 0.100%, Cr: 2.00 to 5 0.000%, Al: 0.001 to 0.50%, N: 0.0020 to 0.0200%, P: 0.001 to 0.050%, and O: 0.0001 to 0.0030%.
- the balance consists of Fe and inevitable impurities, and the total content of Cr, Si, Mn in the steel of the non-carburized part satisfies 2.0 ⁇ Cr + Si + Mn ⁇ 8.0 by mass%,
- the average value of the carbon concentration is 1.00 to 6.7% by mass%.
- the surface layer portion carbide area ratio of is at least 15%, the surface layer portion (Cr, Fe) 23 C 6 and (Cr, Fe) of the 3 C, have one or two precipitates,
- the number of mesh carbides of 10 ⁇ m or more along the old ⁇ grain boundary is 2.5 pieces / mm 2 or less.
- the components of the steel in the non-carburized part are further in mass%, Ca: 0.0005 to 0.0030%, Mg: 0.0005 to 0.0030% , Zr: 0.0005 to 0.0030% of one or more may be contained.
- the component of the steel in the non-carburized part is further in mass%, Mo: 0.01-1.00%, B: 0.0005- One or more of 0.0050%, Cu: 0.05 to 1.00%, and Ni: 0.05 to 2.00% may be contained.
- the component of the steel in the non-carburized part is further in mass%, V: 0.005 to 0.50%, Nb: 0 One or more of 0.005 to 0.10% and Ti: 0.005 to 0.50% may be contained.
- a method for producing a surface hardened steel part according to another aspect of the present invention includes a molding step of forming the steel part by processing the steel for surface hardening according to any one of (1) to (4) above.
- a gas carburizing treatment or a gas carbonitriding treatment in which the carbon potential of the carburizing atmosphere is 0.90% or more for a time of 50% or more of the treatment time is applied to the steel part in a temperature range of 800 to 900 ° C., and the carburized layer And carburizing step of depositing one or two of (Cr, Fe) 23 C 6 and (Cr, Fe) 3 C; and subsequent to the carburizing step, the carburizing treatment or gas carbonitriding treatment was performed.
- the carburizing atmosphere has a carbon potential of 0.40 to 1.20% in a temperature range of 800 to 1100 ° C. before the carburizing step. You may further have the preliminary carburizing process which performs the carburizing process or the gas carbonitriding process to the said steel components.
- the present invention even if the secondary quenching is abolished, it becomes possible to finely disperse the carbide in the carburized layer of the part. As a result, a component having high tooth surface fatigue strength and avoiding an increase in heat treatment deformation (deterioration in dimensional accuracy of the component) due to secondary quenching can be obtained at low cost. For this reason, it is extremely effective for increasing the number of rotations and transmission torque of power transmission parts such as automobiles (for example, gears, bearings, shafts, CVT sheaves, etc.) or reducing the size and weight.
- power transmission parts such as automobiles (for example, gears, bearings, shafts, CVT sheaves, etc.) or reducing the size and weight.
- (B) part is a figure which shows the example of the structure
- a high carbon carburized structure is shown.
- (Cr, Fe) is a diagram showing a 23 C 6 (Cr, Fe) 3 C is precipitated tissue.
- the present inventors diligently studied various factors affecting the dispersion form of carbides in the carburized layer in the high carbon carburizing treatment, and found the following knowledge.
- the carbide generated in the carburized layer during the high carbon carburizing treatment is mainly precipitated as a coarse mesh cementite along the austenite grain boundary when the Cr content in the steel is less than 2.00%.
- the carbide takes a form in which granular or acicular fine carbide is dispersed in the austenite grains.
- the carbide generated in the carburized layer during the high-carbon carburizing treatment becomes finer as the carburizing temperature is lower, and is dispersed as granular or acicular fine carbide in the austenite grains. .
- the carburizing temperature is 900 ° C. or less, a structure in which carbides are sufficiently finely dispersed can be obtained. The reason is as follows.
- the tooth surface fatigue strength can be further improved by further performing a nitriding step (so-called carbonitriding treatment) that is a treatment of adding ammonia to the heat treatment atmosphere following the gas high carbon carburizing treatment.
- a nitriding step that is a treatment of adding ammonia to the heat treatment atmosphere following the gas high carbon carburizing treatment.
- content% of a component means the mass%.
- C 0.10 to 0.60% C is added to ensure the hardness of the core of the component. If the amount of C added is small, the time required for the carburizing process becomes too long. On the other hand, if added excessively, the workability when machining parts such as cutting and forging is significantly deteriorated through an increase in the hardness of the material. To do.
- the C amount needs to be in the range of 0.10 to 0.60%. A preferable range of the amount of C is 0.15 to 0.30%.
- Si 0.01-2.50% Si is an element effective for improving the tooth surface fatigue strength by remarkably increasing the temper softening resistance of low temperature tempered martensitic steel such as carburized parts.
- 0.01% or more of Si is added.
- Si when Si is added excessively, a complex oxide of Cr, Si, and Mn is generated on the surface of the steel material during gas carburization, thereby inhibiting the transfer of carbon from the carburizing atmosphere into the steel material. Therefore, the carbon content of the carburized layer may be lower than the target value.
- the Si amount needs to be in the range of 0.01 to 2.50%.
- a preferable range of Si content is 0.03% to 1.50%, more preferably 0.10% to 1.00%.
- Mn 0.20 to 2.00% Since Mn has the effect of improving the hardenability of steel, 0.20% or more is added to obtain a martensite structure during carburizing and quenching. On the other hand, when added excessively, a complex oxide of Cr, Si, and Mn is generated on the surface of the steel material during gas carburization, thereby inhibiting carbon migration from the carburizing atmosphere into the steel material. Therefore, the carbon content of the carburized layer may be lower than the target value. Moreover, when it adds excessively, the workability at the time of processing, such as cutting and forging of parts, will deteriorate remarkably through the raise of the hardness of a raw material. In the present invention, the amount of Mn needs to be in the range of 0.20 to 2.00%. A preferable range of the amount of Mn is 0.40 to 1.00%.
- S 0.0001 to 0.10% S combines with Mn to form MnS, and the effect of improving the machinability as the addition amount is increased, but if added excessively, MnS becomes a propagation path of fatigue cracks, and the bending of the gear Fatigue strength decreases.
- excessive cost is required to limit the amount of S to 0.0001% or less. Therefore, in the present invention, the S amount needs to be in the range of 0.0001 to 0.10%.
- a preferable range of the amount of S is 0.010 to 0.02%.
- the Cr amount needs to be in the range of 2.00 to 5.00%.
- a preferable Cr content range is 2.00 to 3.50%.
- a more desirable range is 2.25 to 3.00%.
- Al 0.001 to 0.50%
- AlN functions to pin the austenite grain boundaries to suppress grain growth and prevent coarsening of the structure. If the addition amount of Al is small, the above effect cannot be obtained, and the effect is saturated even if it is added excessively. Therefore, in the present invention, the Al amount needs to be in the range of 0.001 to 0.50%. A preferable range of the Al content is 0.020 to 0.15%. When Ti is added in an amount of 0.08% or more, the amount of TiC increases and the pinning effect becomes sufficient, so the Al addition amount may be less than 0.020%.
- N 0.0020 to 0.020%
- N combines with Al in the steel to form AlN.
- AlN functions to pin the austenite grain boundaries to suppress grain growth and prevent coarsening of the structure. If the addition amount of N is small, the above effect cannot be obtained, and if it is added excessively, the ductility at a high temperature range of 1000 ° C. or more is lowered, which causes a decrease in yield during continuous casting and rolling. Therefore, in the present invention, the N amount needs to be in the range of 0.0020 to 0.020%. A preferable range of the N amount is 0.0050 to 0.018%.
- P 0.050% or less P is segregated to austenite grain boundaries, embrittles the prior austenite grain boundaries, and causes grain boundary cracking. Therefore, in this invention, it is necessary to make P amount into the range of 0.050% or less. A preferable range of the amount of P is 0.015% or less. Excessive cost is required to limit the amount of P to 0.001% or less. Therefore, a suitable lower limit of the P amount is 0.001%.
- O 0.0030% or less O forms oxide inclusions.
- O content is large, large inclusions that become the starting point of fatigue failure increase and cause deterioration of fatigue characteristics. Therefore, it is desirable to reduce as much as possible. Therefore, in the present invention, it is necessary to limit the O amount to 0.0030% or less.
- a preferable range of the amount of O is 0.0015% or less. Excessive cost is required to limit the amount of O to 0.0001% or less. Therefore, a preferable lower limit of the O amount is 0.0001%.
- Ca, Mg, Zr 0.0005 to 0.0030%
- Ca, Mg, and Zr are optional components that can be added to the surface hardening steel of the present invention as necessary.
- Ca, Mg, and Zr have the function of improving the machinability of steel through the form control of MnS and the formation of a protective film on the cutting tool surface during cutting.
- one or more of Ca, Mg, and Zr may be added in an amount of 0.0005% or more.
- coarse oxides and sulfides are formed, which may adversely affect the fatigue strength of the parts.
- one or more of Ca, Mg, and Zr may be added in the range of 0.0005 to 0.0030%.
- the preferred range is 0.0008 to 0.0020%.
- the hardness of the material is higher than that of ordinary carburizing steel (such as SCR420 and SCM420 of JISG4053). Accordingly, when a part is molded by cutting, the cutting-related cost may increase due to a shortened life of the cutting tool. That is, since the life of the cutting tool can be extended by adding Ca, Mg, and Zr, adding Ca, Mg, and Zr for the high carbon carburization of the present invention has a great effect on actual production.
- Mo 0.01 to 1.00%
- Mo is an optional component that can be added to the surface hardening steel of the present invention as required. Mo has the effect of enhancing the hardenability of the steel, so it may be added to obtain a martensite structure during carburizing and quenching. Mo does not form oxides in the gas carburizing atmosphere gas atmosphere, and it is difficult to form nitrides. Therefore, Mo-added steel produces oxide layers and nitrides on the surface of the carburized layer and carburized abnormal layers due to it. There is an excellent feature that it is difficult. However, excessive addition is undesirable because the addition cost is expensive. Therefore, in the present invention, the Mo amount may be in the range of 0.01 to 1.00%. A preferable range of Mo content is 0.10 to 0.60%.
- B 0.0005 to 0.0050%
- B is an optional component that can be added to the surface hardening steel of the present invention as required.
- B is in a very small amount in the state of being dissolved in austenite and has the effect of greatly increasing the hardenability of the steel. Therefore, B may be added to obtain a martensitic structure during carburizing and quenching. If the addition amount is too small, the above effect cannot be obtained. On the other hand, even if it is added excessively, the effect is saturated. Therefore, in the present invention, the B amount may be in the range of 0.0005 to 0.0050%. A preferable range of the amount of B is 0.0010 to 0.0025%.
- Cu 0.05 to 1.00%
- Cu is an optional component that can be added to the surface hardening steel of the present invention as required. Since Cu has an effect of improving the hardenability of steel, it may be added to obtain a martensite structure during carburizing and quenching. Since Cu is an element that does not form oxides or nitrides in an atmosphere of gas carburizing, Cu-added steel is unlikely to form an oxide layer or nitride on the surface of the carburized layer, or a carburized abnormal layer resulting therefrom. There is a feature.
- Cu when added excessively, the ductility at a high temperature range of 1000 ° C. or more is lowered, which causes a decrease in yield during continuous casting and rolling. Therefore, in the present invention, Cu may be added in the range of 0.05 to 1.00%. A preferable range of the amount of Cu is 0.010 to 0.50%. In addition, in order to improve the ductility of a high temperature range, when adding Cu, it is desirable to add Ni more than 1/2 of Cu addition amount simultaneously.
- Ni 0.05-2.00%
- Ni is an optional component that can be added to the surface hardening steel of the present invention as required.
- Ni has an effect of improving the hardenability of steel, and may be added to obtain a martensite structure during carburizing and quenching.
- Ni is an element that does not form oxides or nitrides in a gas carburizing atmosphere. Therefore, Ni-added steel is unlikely to generate an oxide layer or nitride on the surface of the carburized layer, or a carburized abnormal layer due to it. There is a feature.
- Ni may be added in the range of 0.05 to 2.00%.
- a preferable range of Ni content is 0.40 to 1.60%.
- V 0.005 to 0.50%
- V is an optional component that can be added to the surface hardening steel of the present invention as required.
- V combines with N and C in steel to form V (C, N).
- V (C, N) functions to pin the austenite grain boundary to suppress grain growth and prevent coarsening of the structure. If the addition amount is small, the above effect cannot be obtained. On the other hand, even if it is added excessively, the effect is saturated.
- V may be added in the range of 0.005 to 0.50%.
- a preferable range of the V amount is 0.05 to 0.20%.
- Nb 0.005 to 0.10%
- Nb is an optional component that can be added to the surface hardening steel of the present invention as required.
- Nb combines with N and C to form Nb (C, N) in steel.
- Nb (C, N) functions to pin the austenite grain boundaries to suppress grain growth and prevent coarsening of the structure. If the addition amount is small, the above effect cannot be obtained. On the other hand, even if it is added excessively, the effect is saturated.
- Nb may be added in the range of 0.005 to 0.10%.
- a preferable range of Nb is 0.010 to 0.050%.
- Ti 0.005 to 0.50%
- Ti is an optional component that can be added to the surface hardening steel of the present invention as required.
- Ti combines with N and C in steel to form Ti (C, N).
- Ti (C, N) functions to pin the austenite grain boundaries to suppress grain growth and prevent coarsening of the structure. If the addition amount is small, the above effect cannot be obtained. On the other hand, even if it is added excessively, the effect is saturated.
- Ti may be added in the range of 0.005 to 0.50%. A preferable range of Ti content is 0.015 to 0.15%.
- the total amount of these three components is within a certain range. It is desirable to regulate with.
- the total content of the three components is set to 2.0% to 8.0%. More preferably, the total content of the three components is 3.0% to 4.5%.
- Pb, Te, Zn, Sn and the like can be added within a range not impairing the effects of the present invention.
- Pb, Te, Zn, and Sn are optional components that can be added to the steel for surface hardening treatment of the present invention as necessary. By adding these elements, the machinability and the like can be improved.
- the upper limit of the addition amount of these additive components is Pb: 0.50% or less, Te: 0.0030% or less, Zn: 0.50% or less, Sn: 0 .. 50% or less.
- the surface hardening-treated steel part of the present invention is subjected to carburizing or carbonitriding using the steel for surface hardening of the present invention.
- the central part (core part) of the part that is not affected by the carburizing process or the carbonitriding process is referred to herein as a non-carburized part.
- the chemical composition of the non-carburized part is substantially the same as the chemical composition of the surface hardened steel part that is the material of the part.
- a region having a depth of 50 ⁇ m from the surface is referred to herein as a surface layer portion.
- the average value of the carbon concentration in the surface layer portion of the carburized layer is 1.00 to 6.7% by mass. If the carbon concentration in the surface layer portion is less than 1.00%, the improvement in the tooth surface fatigue strength is insufficient, and if it is 6.7%, all of the surface layer portion becomes cementite, so that the carbon concentration does not exceed this.
- carbonized_material of the said surface layer part is 15% or more. When the area ratio of carbide is less than 15%, the improvement in tooth surface fatigue strength is insufficient.
- a preferable range of the area ratio of carbide is 20 to 80%.
- the surface layer portion has 100 or more of one or two kinds of precipitates per 100 ⁇ m 2 among (Cr, Fe) 23 C 6 and (Cr, Fe) 3 C.
- the high carbon gas carburizing or high carbon gas carbonitriding conditions of the present invention may be any as long as they comply with the above-mentioned definition of “high carbon gas carburizing or high carbon gas carbonitriding in the present invention”.
- C. P. May be carburized at 0.90% or more.
- C. of the first half time. P. Is 0.80%
- the latter half of C.I. P. May be carburized at 0.90% or more which is a high carbon carburizing atmosphere.
- the C. P. In a high carbon carburizing atmosphere of 0.90% or more. P. May be performed at about 0.80%.
- C.I. P. By changing variously, the carbide fraction of the carburized layer of the part and the amount of retained austenite may be arbitrarily controlled.
- the preferred range is 1.1-1.6%.
- the quenching process performed after carburizing is generally performed by oil cooling, salt bath cooling, gas cooling, etc., but any method may be used.
- oil cooling the preferred range of the temperature of the quenching oil is 50 to 180 ° C. If you want to minimize heat treatment deformation due to quenching, it is desirable to have a low cooling rate (high quenching oil temperature). If you want to minimize the incomplete quenching layer on the surface and increase fatigue strength, use cooling. A higher speed (a lower quenching oil temperature) is desirable.
- Low-temperature tempering 300 ° C. or lower
- Low temperature tempering is performed for the purpose of restoring the toughness of the core of the component and stabilizing the dimensional accuracy and material.
- the surface-hardened steel part of the present invention can be subjected to low-temperature tempering after carburizing and quenching as usual.
- the preferred temperature for tempering in the present invention is 120 to 200 ° C., and the preferred time is 30 to 180 minutes.
- the temperature range of high carbon gas carburization or high carbon gas carbonitriding is set to 800 to 900 ° C.
- the quenching treatment is performed at the temperature at which the carburizing treatment is performed or after cooling to a temperature range equal to or lower than the carburizing treatment temperature. The reason for this will be explained.
- the tooth surface fatigue strength of a component can be improved without performing secondary quenching for fine dispersion of carbide (without deteriorating the dimensional accuracy of the component).
- the carbide generated in the carburized layer during the high carbon carburizing treatment takes a form in which the precipitate becomes finer and the granular or acicular fine carbide is dispersed in the austenite grains as the carburizing temperature is lower. .
- the lower the carburizing treatment temperature the finer the (Cr, Fe) 23 C 6 and / or in the carburized layer at the initial stage of the carburizing treatment.
- (Cr, Fe) 3 C is likely to precipitate in the austenite grains, and the amount of precipitation increases.
- cementite is precipitated with these fine precipitates as nuclei.
- the amount of coarse network cementite produced along the austenite grain boundaries is also suppressed by the above treatment.
- the carburizing temperature is 900 ° C. or less, a structure in which carbides are sufficiently finely dispersed can be obtained.
- carbonized_material increases, so that carburizing process temperature is low, it is advantageous when improving tooth surface fatigue strength.
- the temperature for performing the carburizing process needs to be in the range of 800 to 900 ° C.
- the preferred temperature range for carburizing is 820 to 880 ° C.
- the quenching when quenching is performed after carburizing, the quenching is performed after the temperature is lowered from the carburizing temperature to a certain low temperature for the purpose of reducing heat treatment deformation of the parts before quenching.
- the carburizing temperature since the carburizing temperature is originally low, there is no need to lower the temperature, and there is no problem even if quenching is performed from the temperature at which the carburizing process is performed.
- quenching may be performed after the temperature is lowered to a temperature lower than the carburizing temperature, but when the temperature is too low, C.I. P. Problems with control and atmosphere safety.
- a preferable range of the quenching start temperature is 760 to 850 ° C.
- the carbon potential of the carburizing atmosphere is 0.40 to 1 in the temperature range of 800 to 1100 ° C. before the high carbon carburizing treatment at 800 to 900 ° C. as described above. It may further include a preliminary carburizing step in which a gas carburizing process or a gas carbonitriding process is performed on the steel part under a condition of 20%. As described above, when the high carbon carburizing treatment is performed, the lower the carburizing treatment temperature, the finer (Cr, Fe) 23 C 6 and / or (Cr, Fe) 3 C in the carburized layer at the initial stage of the carburizing treatment.
- carburizing or carbonitriding is performed under normal conditions, and subsequently, the temperature is lowered to a range of 800 to 900 ° C. and high-concentration carburizing or high-concentration carbonitriding is performed. Good.
- the carburizing time can be shortened and the productivity can be improved.
- the carburizing condition needs to be performed in a temperature range of 800 to 1100 ° C. If it is less than 800 degreeC, the effect of a hardened layer depth improvement will not be acquired, but it is meaningless.
- the preferred temperature range is 900-1000 ° C.
- the carbon potential in the carburizing atmosphere must be 0.40 to 1.20%. If it is less than 0.40%, the effect of improving the depth of the hardened layer is small. If it exceeds 1.20%, coarse reticulated cementite precipitates before the carburizing treatment at low temperature and high concentration, and then does not disappear. The characteristics as a part are impaired.
- the preferred carbon potential range is 0.60 to 1.00%.
- (Cr, Fe) 23 C 6 and / or (Cr, Fe) 3 C are precipitated in the carburized layer during the high carbon / low temperature carburizing treatment.
- (Cr, Fe) 23 C 6 is a carbide in which Cr and Fe are the main constituent elements, but it is not limited to purely containing only Cr, Fe and C, and other elements such as Mo and Mn.
- the alloy element may be included.
- ⁇ Shot peening treatment may be performed after carburizing treatment on the surface-hardening treated parts produced by the steel of the present invention.
- the increase in the compressive residual stress of the component surface layer introduced by the shot peening process suppresses the occurrence and development of fatigue cracks, so that the tooth root and tooth surface fatigue strength of the component manufactured by the steel of the present invention are further increased.
- the shot peening treatment is desirably performed using shot grains having a diameter of 0.7 mm or less and an arc height of 0.4 mm or more.
- the conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited.
- the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
- (Example) Converter molten steel having the component composition shown in Tables 1 and 2 was manufactured by continuous casting, and subjected to a soaking diffusion treatment as necessary, and through a split rolling process, a 162 mm square rolled material was obtained. Next, a steel bar shape with a diameter of 35 mm was formed by hot rolling.
- hot forging simulation was performed under the condition that the hot-rolled steel material was heated at 1250 ° C. for 30 minutes and then air-cooled. . Subsequently, normalization was performed under the conditions of heating at 925 ° C. for 60 minutes and then gradually cooling. 20 pieces of roller pitching test pieces having a large diameter portion (test portion) 26 ⁇ and 20 smooth Ono-type rotating bending fatigue test pieces having a smooth portion 8 ⁇ were produced from the thus prepared materials by machining.
- FIGS. 1A to 1O The produced test specimens were subjected to gas carburizing treatment or gas carbonitriding treatment with patterns shown in FIGS. 1A to 1O.
- 1A to 1I and FIGS. 1N and 1O are carburizing patterns that meet the conditions of the present invention, and FIGS. 1K, 1L, and 1M are carburizing patterns for comparison.
- all test pieces were tempered under the conditions of heating at 150 ° C. for 90 minutes and then air cooling. Thereafter, in order to improve the test accuracy of the fatigue test, the gripping portions of the roller pitching test piece and the smooth Ono type rotating bending fatigue test piece were finished.
- the structure was observed from the outermost surface to a depth of 200 ⁇ m, and when reticulated cementite was present along the old ⁇ grain boundary, it was determined that “reticulated carbide was present”.
- a visual field corresponding to 0.5 mm 2 was examined at 5 magnifications at each observation position at a magnification of 400 times.
- the average density of the net-like carbide is 2.5 pieces / mm 2 or more.
- FIG. 2 An example of a structure in which reticulated cementite is present is shown in part (a) of FIG. 2, and an example of a good high carbon carburized structure in which reticulated cementite is not present and fine carbides are dispersed in a large amount. Is shown in part (b) of FIG.
- FIG. 3 shows an example in which (Cr, Fe) 23 C 6 and (Cr, Fe) 3 C are precipitated in the carburized layer.
- roller pitching test was conducted under the conditions of a large roller: SCM420 carburized product, crowning 150R, rotation speed: 2000 rpm, lubricating oil: transmission oil, oil temperature 80 ° C, slip rate -40%, maximum 10 million cycles.
- a diagram was created to determine the fatigue limit, which was defined as the roller pitting fatigue strength. Those having a roller pitting fatigue strength of less than 3000 MPa were judged to have inferior tooth surface fatigue strength.
- the smooth Ono type rotating bending fatigue test was performed under the condition of the number of revolutions: 3000 rpm, an SN diagram was created to determine the fatigue limit, and the rotating bending fatigue strength was obtained.
- the smooth Ono type rotating bending fatigue strength did not reach 600 MPa, it was determined that the tooth root bending fatigue strength was inferior.
- the Si addition amount, the Mn addition amount, and the Cr addition amount are larger than the range of the present invention.
- composite oxides of Cr, Si, and Mn were formed on the surface of the steel material, and the amount of carbon in the carburized layer was significantly reduced.
- the amount of precipitated carbide was insufficient.
- the hardness of the surface layer itself as a carburized part was insufficient, and both the roller pitching strength and the rotational bending fatigue strength were insufficient.
- the present invention even if the secondary quenching is abolished, it becomes possible to finely disperse the carbide in the carburized layer of the component, and it has a high tooth surface fatigue strength and is suitable for the secondary quenching.
- a component that avoids the increase in heat treatment deformation (deterioration of component accuracy) caused by this can be obtained at low cost. For this reason, it is extremely effective in increasing the rotational speed and transmission torque of power transmission parts such as automobiles (for example, gears, bearings, shafts, CVT sheaves, etc.) or reducing the size and weight.
- the present invention can greatly contribute not only to the improvement of the performance of conventional automobiles but also to the improvement of the performance of hybrid cars and electric cars and the spread of such cars through such effects. The nature is great.
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Abstract
Description
本願は、2010年3月19日に、日本に出願された特願2010-064880号に基づき優先権を主張し、その内容をここに援用する。
高炭素浸炭処理と通常浸炭処理との区別はあいまいであり、厳密な区別や一般的な定義は存在しない。本発明では、高炭素浸炭処理を「全浸炭処理時間の50%以上の時間において、C.P.が0.90%以上である浸炭処理」と定義する。
Cは、部品の心部の硬さを確保するために添加する。C添加量が少ないと、浸炭処理に要する時間が長くなりすぎ、一方、過剰に添加すると、素材の硬さの上昇を通じて、部品の切削・鍛造等の加工を行うときの加工性が顕著に劣化する。本発明では、C量を0.10~0.60%の範囲にする必要がある。好適なC量の範囲は0.15~0.30%である。
Siは、浸炭部品のような低温焼戻しマルテンサイト鋼の焼戻し軟化抵抗を顕著に増加することによって、歯面疲労強度を向上するのに有効な元素である。本発明では、Siを、0.01%以上添加する。しかし、Siを過剰に添加すると、ガス浸炭時に、Cr、Si、Mnの複合酸化物が鋼材表面に生成し、浸炭雰囲気から鋼材中への炭素の移行を阻害する。そのため、浸炭層の炭素量が、目標とする値よりも低下する場合がある。また、Siを過剰に添加すると、素材の硬さの上昇を通じて、部品の切削・鍛造等の加工を行うときの加工性が顕著に劣化する。本発明では、Si量を0.01~2.50%の範囲にする必要がある。好適なSi量の範囲は0.03%~1.50%、更に好ましくは0.10%~1.00%である。
Mnは、鋼の焼入れ性を高める効果があるので、浸炭焼入れ時にマルテンサイト組織を得るために、0.20%以上添加する。一方、過剰に添加すると、ガス浸炭時に、Cr、Si、Mnの複合酸化物が鋼材表面に生成し、浸炭雰囲気から鋼材中への炭素の移行を阻害する。そのため、浸炭層の炭素量が目標とする値よりも低下する場合がある。また、過剰に添加すると、素材の硬さの上昇を通じて、部品の切削・鍛造等の加工を行うときの加工性が顕著に劣化する。本発明では、Mn量を0.20~2.00%の範囲にする必要がある。好適なMn量の範囲は0.40~1.00%である。
Sは、Mnと結合してMnSを形成し、添加量を増加するほど、被削性を向上させる効果を持つが、過剰に添加すると、MnSが疲労亀裂の伝播経路となって、歯車の曲げ疲労強度が低下する。また、S量を0.0001%以下に制限するには過剰なコストがかかる。従って、本発明では、S量を0.0001~0.10%の範囲にする必要がある。S量の好適範囲は0.010~0.02%である。
Crは、添加量が多いほど、高炭素浸炭処理時に、浸炭層に生成する炭化物の析出量が増加する。また、Crの添加量が所定の量以上の場合に、浸炭処理の初期に浸炭層において、微細な(Cr、Fe)23C6、及び/又は(Cr、Fe)3Cが、オーステナイト粒内に析出し易くなり、また、析出量も増加する。浸炭処理の後期には、これらの微細析出物を核としてセメンタイトが析出するので、炭化物の微細分散化と、オーステナイト粒界に沿った粗大な網目状のセメンタイトの抑制に対して、極めて有効な元素であるので、比較的多量に添加する。
Alは、鋼の脱酸のために有効な元素であるとともに、鋼中でNと結合してAlNを形成する。AlNは、オーステナイト結晶粒界をピン止めして粒成長を抑制し、組織の粗大化を防止する働きをする。Alの添加量が少ないと、上記の効果が得られず、過剰に添加しても効果が飽和する。従って、本発明ではAl量を0.001~0.50%の範囲にする必要がある。Al量の好適な範囲は0.020~0.15%である。なお、Tiが0.08%以上添加される場合には、TiCの量が増加し、ピン止め効果が十分になるので、Al添加量は0.020%よりも少なくてよい。
Nは、鋼中でAlと結合してAlNを形成する。AlNは、オーステナイト結晶粒界をピン止めして粒成長を抑制して、組織の粗大化を防止する働きをする。Nの添加量が少ないと、上記の効果が得られず、過剰に添加すると、1000℃以上の高温域における延性が低下し、連続鋳造、圧延時の歩留まり低下の原因になる。従って、本発明ではN量を、0.0020~0.020%の範囲にする必要がある。N量の好適な範囲は0.0050~0.018%である。
Pは、オーステナイト粒界に偏析して、旧オーステナイト粒界を脆化させて、粒界割れの原因となるので、できるだけ低減することが望ましい。そのため、本発明では、P量を0.050%以下の範囲にする必要がある。P量の好適な範囲は0.015%以下である。P量を0.001%以下に制限するには過剰なコストがかかる。従って、P量の好適な下限は0.001%である。
Oは、酸化物系介在物を形成する。O含有量が多い場合は、疲労破壊の起点となる大きな介在物が増加し、疲労特性の低下の原因となるので、できるだけ低減することが望ましい。そのため、本発明ではO量を0.0030%以下に制限する必要がある。O量の好適範囲は0.0015%以下である。O量を0.0001%以下に制限するには過剰なコストがかかる。そのため、好適なO量の下限は0.0001%である。
Ca、Mg、Zrは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Ca、Mg、ZrはMnSの形態制御、及び切削時の切削工具表面における保護被膜形成を通じて鋼の被削性を向上する働きがある。この効果を得るために、Ca、Mg、Zrのうちの1種または2種以上を各0.0005%以上添加してもよい。一方、0.0030%を超えて添加すると、粗大な酸化物や硫化物を形成して部品の疲労強度に悪影響を与える場合がある。従って本発明では、Ca、Mg、Zrのうちの1種または2種以上をそれぞれ0.0005~0.0030%の範囲で添加してもよい。好適範囲は0.0008~0.0020%である。本願発明のような比較的Cr添加量の多い鋼種の場合、通常の浸炭用鋼(JISG4053のSCR420、SCM420等)よりも素材の硬さが高めになる。従って、部品を切削加工で成型する場合に、切削工具の寿命が短くなることによって、切削に関わるコストが高くなる場合がある。すなわち、Ca、Mg、Zrを添加することによって切削工具の寿命を延長することができるため、本願発明の高炭素浸炭用にCa、Mg、Zrを添加することは実生産上の効果が大きい。
Moは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Moは、鋼の焼入れ性を高める効果があるので、浸炭焼入れ時に、マルテンサイト組織を得るために添加してもよい。Moは、ガス浸炭の雰囲気ガス雰囲気では酸化物を形成せず、窒化物を形成し難いので、Mo添加鋼は、浸炭層表面の酸化物層や窒化物、それに起因する浸炭異常層を生成し難いという優れた特徴がある。しかし、添加コストが高価であるので、過剰の添加は望ましくない。そのため、本発明では、Mo量を0.01~1.00%の範囲にしてもよい。好適なMo量の範囲は0.10~0.60%である。
Bは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Bは、オーステナイト中に固溶している状態において、微量で、鋼の焼入れ性を大きく高める効果があるので、浸炭焼入れ時に、マルテンサイト組織を得るために添加してもよい。添加量が少なすぎると、上記の効果が得られず、一方、過剰に添加しても、効果が飽和する。従って、本発明ではB量を、0.0005~0.0050%の範囲にしてもよい。好適なB量の範囲は0.0010~0.0025%である。
Cuは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Cuは、鋼の焼入れ性を高める効果があるので、浸炭焼入れ時に、マルテンサイト組織を得るために添加してもよい。Cuは、ガス浸炭の雰囲気ガス雰囲気では、酸化物や窒化物を形成しない元素であるので、Cu添加鋼は、浸炭層表面の酸化物層や窒化物、それに起因する浸炭異常層を生成し難いという特徴がある。
Niは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Niは、鋼の焼入れ性を高める効果があるので、浸炭焼入れ時に、マルテンサイト組織を得るために添加してもよい。Niは、ガス浸炭の雰囲気ガス雰囲気では、酸化物や窒化物を形成しない元素であるので、Ni添加鋼は、浸炭層表面の酸化物層や窒化物、それに起因する浸炭異常層を生成し難いという特徴がある。
Vは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Vは、鋼中で、N、Cと結合して、V(C、N)を形成する。V(C、N)は、オーステナイト結晶粒界をピン止めして粒成長を抑制し、組織の粗大化を防止する働きをする。添加量が少ないと、上記の効果が得られず、一方、過剰に添加しても、効果が飽和する。本発明では、Vを0.005~0.50%の範囲で添加してもよい。V量の好適な範囲は0.05~0.20%である。
Nbは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Nbは、鋼中で、N、Cと結合してNb(C、N)を形成する。Nb(C、N)は、オーステナイト結晶粒界をピン止めして粒成長を抑制し、組織の粗大化を防止する働きをする。添加量が少ないと、上記の効果が得られず、一方、過剰に添加しても、効果が飽和する。本発明では、Nbを0.005~0.10%の範囲で添加してもよい。Nbの好適な範囲は0.010~0.050%である。
Tiは必要に応じて本発明の表層硬化処理用鋼に添加可能な任意成分である。Tiは、鋼中で、N、Cと結合して、Ti(C、N)を形成する。Ti(C、N)は、オーステナイト結晶粒界をピン止めして粒成長を抑制し、組織の粗大化を防止する働きをする。添加量が少ないと、上記の効果が得られず、一方、過剰に添加しても、効果が飽和する。本発明では、Tiを0.005~0.50%の範囲で添加してもよい。Ti量の好適な範囲は0.015~0.15%である。
鋼中のCr、Si、Mnの各元素量に応じて、ガス浸炭時に、Cr、Si、Mnの複合酸化物が鋼材表面に生成し、浸炭雰囲気から鋼材中への炭素の移行が阻害される。従って、高炭素浸炭において部品の表層部の炭素量を確保し、(Cr、Fe)23C6や(Cr、Fe)3Cを析出させるためには、これら3成分の合計量を一定の範囲で規制するのが望ましい。本発明では、上記3成分の合計含有量を2.0%~8.0%とする。より望ましい上記3成分の合計含有量は3.0%~4.5%である。
鋼部品の浸炭層のうち、表面から50μm深さの領域をここでは表層部と呼ぶ。本発明の表層硬化処理鋼部品で、浸炭層の表層部の炭素濃度の平均値は質量%で1.00~6.7%である。表層部の炭素濃度が1.00%未満では歯面疲労強度の向上が不十分であり、6.7%で表層部の全てがセメンタイトになるため、これ以上の炭素濃度にはならない。また、上記表層部(表面から50μm深さの領域)の炭化物の面積率は15%以上である。炭化物の面積率が15%未満の場合は、歯面疲労強度の向上が不十分である。炭化物の面積率の好適範囲は20~80%である。表層部は(Cr、Fe)23C6及び(Cr、Fe)3Cのうち、1種または2種の析出物を100μm2あたり100個以上有する。
前述のように、高炭素浸炭処理を行った場合、浸炭処理温度が低いほど浸炭処理の初期に浸炭層において微細な(Cr,Fe)23C6、又は/及び(Cr,Fe)3Cがオーステナイト粒内に析出しやすくなり、また析出量も増加する。そして、浸炭処理の後期にはこれらの微細析出物を核としてセメンタイトが析出する。
他方、浸炭処理温度が低い場合は炭素の拡散距離が短いため、有効硬化層深さが浅めになり、所望の有効硬化層深さを得るための浸炭時間が長めになるという欠点がある。しかし、この低温・高炭素浸炭処理の前に、予備浸炭工程を行うことが出来る。この予備浸炭工程は、粗大な網目状のセメンタイトが析出しない浸炭条件であれば、どのような条件で浸炭を行っても、引き続いて行う低温・高濃度浸炭処理に悪影響は与えない。従って、炭素をより深い位置まで拡散させるために、まず通常の条件で浸炭又は浸炭窒化を行い、引き続いて800~900℃の範囲に降温して高濃度浸炭又は高濃度浸炭窒化処理を施してもよい。この場合、有効硬化層深さの向上と高濃度浸炭による歯面疲労強度の向上が両立できるので、浸炭時間の短縮につながり、生産性の向上を図ることができる。通常浸炭の条件は800~1100℃の温度範囲で行う必要がある。800℃未満では硬化層深さ向上の効果が得られず、意味がない。1100℃を超えると結晶粒が顕著に粗大化し、浸炭部品としての特性を損なう。好適な温度範囲は900~1000℃である。浸炭雰囲気のカーボンポテンシャルは0.40~1.20%の条件で行う必要がある。0.40%未満では硬化層深さ向上の効果が小さく、1.20%を超えると低温・高濃度浸炭処理を施す前に粗大な網目状セメンタイトが析出し、その後消えることはないため、浸炭部品としての特性を損なう。好適なカーボンポテンシャルの範囲は0.60~1.00%である。
表1、2に示す成分組成を有する転炉溶製鋼を連続鋳造により製造し、必要に応じて、均熱拡散処理を施し、分塊圧延工程を経て、162mm角の圧延素材とした。次に、熱間圧延によって、直径が35mmの棒鋼形状とした。
表3中、鋼No.、浸炭パターン、炭化物面積率、(Cr,Fe)23C6 と(Cr,Fe)3Cの析出有無の欄で、下線はその数値が本発明の範囲外であることを意味する。また、網目状炭化物の有無、ローラーピッチング疲労強度、回転曲げ疲労強度の下線は、その数値が目標未達成であることを意味する。
製造No.46は鋼中のCr、Si、Mnの合計添加量が多すぎるため、ガス浸炭時に、Cr、Si、Mnの複合酸化物が鋼材表面に生成し、浸炭処理後も表面の炭素濃度が全く増加していなかった。このため炭化物も全く析出せず、浸炭部品としての表層の硬さ自体も不足して、ローラーピッチング強度、回転曲げ疲労強度ともに、不十分だった。
Claims (10)
- 800~900℃の温度域で浸炭処理される表層硬化処理用鋼であって、
化学成分が、質量%で、
C:0.10~0.60%、
Si:0.01~2.50%、
Mn:0.20~2.00%、
S:0.0001~0.10%、
Cr:2.00~5.00%、
Al:0.001~0.50%、
N:0.0020~0.020%、
P:0.001~0.050%、及び、
O:0.0001~0.0030%、
を含有し、
残部がFe及び不可避的不純物からなり、
Cr、Si、Mnの合計含有量が、質量%で2.0≦Cr+Si+Mn≦8.0を満たす
ことを特徴とする表層硬化処理用鋼。 - 前記化学成分が、更に、質量%で、
Ca:0.0005~0.0030%、
Mg:0.0005~0.0030%、
Zr:0.0005~0.0030%
の内の1種または2種以上を含有することを特徴とする請求項1に記載の表層硬化処理用鋼。 - 前記化学成分が、更に、質量%で、
Mo:0.01~1.00%、
B:0.0005~0.0050%、
Cu:0.05~1.00%、及び、
Ni:0.05~2.00%の1種又は2種以上を含有することを特徴とする請求項1または2に記載の表層硬化処理用鋼。 - 前記化学成分が、更に、質量%で、
V:0.005~0.50%、
Nb:0.005~0.10%、及び、
Ti:0.005~0.50%の1種又は2種以上を含有することを特徴とする請求項1または2に記載の表層硬化処理用鋼。 - 浸炭処理又は浸炭窒化処理が施された鋼部品であって、
前記鋼部品の非浸炭部の鋼の成分が、質量%で、
C:0.10~0.60%、
Si:0.01~2.50%、
Mn:0.20~2.00%、
S:0.0001~0.100%、
Cr:2.00~5.00%、
Al:0.001~0.50%、
N:0.0020~0.0200%、
P:0.001~0.050%、及び、
O:0.0001~0.0030%、を含有し、
残部がFe及び不可避的不純物からなり、
前記非浸炭部の鋼のCr、Si、Mnの合計含有量が、質量%で2.0≦Cr+Si+Mn≦8.0を満たし、
浸炭層の最表面から50μm深さまでの部分である表層部で、炭素濃度の平均値が質量%で1.00~6.7%であり、
前記表層部の炭化物の面積率が15%以上であり、
前記表層部が(Cr、Fe)23C6及び(Cr、Fe)3Cのうち、1種または2種の析出物を有し、
前記表層部で、旧γ粒界に沿った10μm以上の網目状炭化物が2.5個/mm2以下である
ことを特徴とする表層硬化鋼部品。 - 非浸炭部の前記鋼の成分が、更に、質量%で、
Ca:0.0005~0.0030%、
Mg:0.0005~0.0030%、
Zr:0.0005~0.0030%
の内の1種または2種以上を含有することを特徴とする請求項5に記載の表面硬化鋼部品。 - 非浸炭部の前記鋼の成分が、更に、質量%で、
Mo:0.01~1.00%、
B:0.0005~0.0050%、
Cu:0.05~1.00%、及び、
Ni:0.05~2.00%、
の内の1種又は2種以上を含有することを特徴とする請求項5または6に記載の表層硬化鋼部品。 - 非浸炭部の前記鋼の成分が、更に、質量%で、
V:0.005~0.50%、
Nb:0.005~0.10%、及び
Ti:0.005~0.50%、
の1種又は2種以上を含有することを特徴とする請求項5または6に記載の表層硬化鋼部品。 - 請求項1または2に記載の表層硬化処理用鋼を加工して鋼部品を成型する成型工程と;
処理時間の50%以上の時間において、浸炭雰囲気のカーボンポテンシャルが0.90%以上であるガス浸炭処理又はガス浸炭窒化処理を、800~900℃の温度域で前記鋼部品に施し、浸炭層に、(Cr、Fe)23C6及び(Cr、Fe)3Cの1種又は2種を析出させる、浸炭工程と;
前記浸炭工程に続いて、前記浸炭処理又はガス浸炭窒化処理を行った温度のまま、又は、浸炭処理温度以下の温度域に冷却した後に、焼入れ処理を施す焼入れ工程と;
を有することを特徴とする表層硬化鋼部品の製造方法。 - 前記浸炭工程の前に、800~1100℃の温度域で浸炭雰囲気のカーボンポテンシャルが0.40~1.20%の条件でガス浸炭処理又はガス浸炭窒化処理を前記鋼部品に施す、予備浸炭工程を更に有することを特徴とする請求項9に記載の表層硬化鋼部品の製造方法。
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JP2014201811A (ja) * | 2013-04-08 | 2014-10-27 | 本田技研工業株式会社 | 浸炭部品、その製造方法及び浸炭部品用鋼 |
US10428414B2 (en) * | 2013-06-26 | 2019-10-01 | Daido Steel Co., Ltd. | Carburized component |
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JP2015045036A (ja) * | 2013-08-27 | 2015-03-12 | 山陽特殊製鋼株式会社 | 水素環境下における耐ピッチング特性に優れる歯車用はだ焼鋼 |
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Also Published As
Publication number | Publication date |
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EP2514847B1 (en) | 2014-12-17 |
US20120018050A1 (en) | 2012-01-26 |
US8475605B2 (en) | 2013-07-02 |
EP2514847A1 (en) | 2012-10-24 |
CN102341520A (zh) | 2012-02-01 |
EP2514847A4 (en) | 2013-08-28 |
CN102341520B (zh) | 2014-02-26 |
KR20110128282A (ko) | 2011-11-29 |
KR101247478B1 (ko) | 2013-04-01 |
JPWO2011114836A1 (ja) | 2013-06-27 |
JP4927234B2 (ja) | 2012-05-09 |
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