EP3299487B2 - Method for surface hardening a cold deformed article comprising low temperature annealing - Google Patents
Method for surface hardening a cold deformed article comprising low temperature annealing Download PDFInfo
- Publication number
- EP3299487B2 EP3299487B2 EP16190934.6A EP16190934A EP3299487B2 EP 3299487 B2 EP3299487 B2 EP 3299487B2 EP 16190934 A EP16190934 A EP 16190934A EP 3299487 B2 EP3299487 B2 EP 3299487B2
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- 238000000034 method Methods 0.000 title claims description 71
- 238000000137 annealing Methods 0.000 title claims description 44
- 239000012298 atmosphere Substances 0.000 claims description 71
- 150000001875 compounds Chemical class 0.000 claims description 58
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 42
- 238000009792 diffusion process Methods 0.000 claims description 35
- 238000010438 heat treatment Methods 0.000 claims description 35
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 31
- 229910052799 carbon Inorganic materials 0.000 claims description 31
- 238000005260 corrosion Methods 0.000 claims description 26
- 230000007797 corrosion Effects 0.000 claims description 26
- 239000000203 mixture Substances 0.000 claims description 25
- 229910045601 alloy Inorganic materials 0.000 claims description 23
- 239000000956 alloy Substances 0.000 claims description 23
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 21
- 229910052804 chromium Inorganic materials 0.000 claims description 21
- 239000011651 chromium Substances 0.000 claims description 21
- 229910052757 nitrogen Inorganic materials 0.000 claims description 21
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 20
- 229910001220 stainless steel Inorganic materials 0.000 claims description 20
- 238000005121 nitriding Methods 0.000 claims description 19
- 239000010935 stainless steel Substances 0.000 claims description 19
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 18
- 230000004913 activation Effects 0.000 claims description 15
- -1 nitrogen containing compound Chemical class 0.000 claims description 15
- 239000001257 hydrogen Substances 0.000 claims description 14
- 229910052739 hydrogen Inorganic materials 0.000 claims description 14
- 238000005255 carburizing Methods 0.000 claims description 13
- 150000003839 salts Chemical class 0.000 claims description 13
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 12
- 150000002430 hydrocarbons Chemical class 0.000 claims description 12
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 10
- 239000001569 carbon dioxide Substances 0.000 claims description 10
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 10
- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 10
- 229910052731 fluorine Inorganic materials 0.000 claims description 10
- 239000011737 fluorine Substances 0.000 claims description 10
- 229910052759 nickel Inorganic materials 0.000 claims description 9
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 7
- 150000002431 hydrogen Chemical class 0.000 claims description 7
- 150000004767 nitrides Chemical class 0.000 claims description 7
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 7
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 6
- 229910021529 ammonia Inorganic materials 0.000 claims description 6
- 239000004202 carbamide Substances 0.000 claims description 6
- 238000003754 machining Methods 0.000 claims description 6
- 238000007493 shaping process Methods 0.000 claims description 6
- 238000001125 extrusion Methods 0.000 claims description 5
- 150000002222 fluorine compounds Chemical class 0.000 claims description 5
- 229910000963 austenitic stainless steel Inorganic materials 0.000 claims description 4
- 238000005242 forging Methods 0.000 claims description 4
- 238000000227 grinding Methods 0.000 claims description 4
- 238000003801 milling Methods 0.000 claims description 4
- 238000005498 polishing Methods 0.000 claims description 4
- 238000003825 pressing Methods 0.000 claims description 4
- 238000004080 punching Methods 0.000 claims description 4
- 238000005096 rolling process Methods 0.000 claims description 4
- 238000007514 turning Methods 0.000 claims description 4
- 230000003213 activating effect Effects 0.000 claims description 3
- 150000001335 aliphatic alkanes Chemical class 0.000 claims description 3
- XPDWGBQVDMORPB-UHFFFAOYSA-N Fluoroform Chemical compound FC(F)F XPDWGBQVDMORPB-UHFFFAOYSA-N 0.000 claims description 2
- 229910004014 SiF4 Inorganic materials 0.000 claims description 2
- 150000001336 alkenes Chemical class 0.000 claims description 2
- 150000001345 alkine derivatives Chemical class 0.000 claims description 2
- 229910001039 duplex stainless steel Inorganic materials 0.000 claims description 2
- ABTOQLMXBSRXSM-UHFFFAOYSA-N silicon tetrafluoride Chemical compound F[Si](F)(F)F ABTOQLMXBSRXSM-UHFFFAOYSA-N 0.000 claims description 2
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 claims 1
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 12
- 239000002244 precipitate Substances 0.000 description 12
- 230000008569 process Effects 0.000 description 12
- 238000005482 strain hardening Methods 0.000 description 10
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 9
- 230000015572 biosynthetic process Effects 0.000 description 9
- 239000007789 gas Substances 0.000 description 9
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 8
- 239000000460 chlorine Substances 0.000 description 8
- 229910052801 chlorine Inorganic materials 0.000 description 8
- 229910052786 argon Inorganic materials 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 230000008901 benefit Effects 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 4
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 238000000354 decomposition reaction Methods 0.000 description 4
- 239000003085 diluting agent Substances 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 239000011261 inert gas Substances 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 229910001256 stainless steel alloy Inorganic materials 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910000734 martensite Inorganic materials 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- CXOWYMLTGOFURZ-UHFFFAOYSA-N azanylidynechromium Chemical compound [Cr]#N CXOWYMLTGOFURZ-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- GVEHJMMRQRRJPM-UHFFFAOYSA-N chromium(2+);methanidylidynechromium Chemical compound [Cr+2].[Cr]#[C-].[Cr]#[C-] GVEHJMMRQRRJPM-UHFFFAOYSA-N 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000004049 embossing Methods 0.000 description 2
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 150000002825 nitriles Chemical class 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000009832 plasma treatment Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 229910003470 tongbaite Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 description 1
- 229910001626 barium chloride Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- KXZJHVJKXJLBKO-UHFFFAOYSA-N chembl1408157 Chemical compound N=1C2=CC=CC=C2C(C(=O)O)=CC=1C1=CC=C(O)C=C1 KXZJHVJKXJLBKO-UHFFFAOYSA-N 0.000 description 1
- 238000010273 cold forging Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- WMIYKQLTONQJES-UHFFFAOYSA-N hexafluoroethane Chemical compound FC(F)(F)C(F)(F)F WMIYKQLTONQJES-UHFFFAOYSA-N 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
- NNFCIKHAZHQZJG-UHFFFAOYSA-N potassium cyanide Chemical compound [K+].N#[C-] NNFCIKHAZHQZJG-UHFFFAOYSA-N 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 229910001631 strontium chloride Inorganic materials 0.000 description 1
- AHBGXTDRMVNFER-UHFFFAOYSA-L strontium dichloride Chemical compound [Cl-].[Cl-].[Sr+2] AHBGXTDRMVNFER-UHFFFAOYSA-L 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- SFZCNBIFKDRMGX-UHFFFAOYSA-N sulfur hexafluoride Chemical compound FS(F)(F)(F)(F)F SFZCNBIFKDRMGX-UHFFFAOYSA-N 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- NXHILIPIEUBEPD-UHFFFAOYSA-H tungsten hexafluoride Chemical compound F[W](F)(F)(F)(F)F NXHILIPIEUBEPD-UHFFFAOYSA-H 0.000 description 1
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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
- C23C8/02—Pretreatment of the material to be coated
-
- 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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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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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
- C21D7/00—Modifying the physical properties of iron or steel by deformation
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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
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
- C21D7/10—Modifying the physical properties of iron or steel by deformation by cold working of the whole cross-section, e.g. of concrete reinforcing bars
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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
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
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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
- C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
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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
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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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- 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
- C23C8/24—Nitriding
- C23C8/26—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
- C23C8/28—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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- 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
- C23C8/36—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 using ionised gases, e.g. ionitriding
- C23C8/38—Treatment 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
- C23C8/40—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 liquids, e.g. salt baths, liquid suspensions
- C23C8/42—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 liquids, e.g. salt baths, liquid suspensions only one element being applied
- C23C8/44—Carburising
- C23C8/46—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
- C23C8/40—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 liquids, e.g. salt baths, liquid suspensions
- C23C8/42—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 liquids, e.g. salt baths, liquid suspensions only one element being applied
- C23C8/48—Nitriding
- C23C8/50—Nitriding 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
- C23C8/40—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 liquids, e.g. salt baths, liquid suspensions
- C23C8/52—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 liquids, e.g. salt baths, liquid suspensions more than one element being applied in one step
- C23C8/54—Carbo-nitriding
- C23C8/56—Carbo-nitriding of ferrous surfaces
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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
- C21D1/26—Methods of annealing
Definitions
- the present invention relates to a method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight. Moreover, the present invention relates to a surface hardened cold deformed article obtainable with this method.
- Articles such as metal articles made of steel or a nickel base alloy, are often shaped by means of cold deformation, such as extrusion or cold forging.
- Cold deformation is a method for strengthening a metal by plastic deformation, which is usually performed in the course of shaping an article at a temperature below the recrystallization temperature of the material, from which the article is made.
- Stainless steels such as austenitic stainless steel, usually have an excellent corrosion resistance, toughness and weldability, but have a comparable low yield strength as well as a comparable low wear resistance.
- Cold forming improves the yield strength of such articles on account of structural changes, i.e. in particular changes of the microstructure, such as the formation of martensite and the like, in the steel occurring as consequence of the plastic deformation occurring during the cold working.
- such articles are often also diffusion hardened in addition to the cold working, by subjecting the articles to a heat treatment at a temperature of typically 350 to 510°C in an atmosphere comprising a chemical compound forming during the heat treatment a species, which diffuses into the surface of the articles and thus improves the characteristics of the articles.
- Most prominent diffusion hardening methods are carburizing, nitriding and nitrocarburizing. While carbon diffuses during carburization into the surface area of the article, nitrogen diffuses during nitriding, carbon and nitrogen diffuse during nitrocarburizing and boron diffuses during boriding into the surface area of the article.
- Carburization for example, is performed by heat treating the article in an atmosphere containing for instance an alkane, such as propane, and optionally further including hydrogen at 500°C for 10 hours.
- the article has to be activated during or better before the carburization, in order to remove the oxide layer of the article, which would act during the carburization as barrier.
- Such an activation is usually performed in a fluorine compound containing atmosphere, such as in a gaseous atmosphere comprising NF 3 at a temperature of 250 to 500°C, such as for instance described in EP 0 678 589 A1 .
- a major disadvantage of diffusion hardening cold worked articles made of stainless steel or comparable alloys is that as consequence of the microstructural changes of the stainless steel or alloy, respectively, occurred during the cold working, compounds consisting of the diffusion element and of chromium from the stainless steel or alloy, respectively, precipitate during the diffusion hardening.
- compounds consisting of the diffusion element and of chromium from the stainless steel or alloy, respectively precipitate during the diffusion hardening.
- chromium carbide precipitates in the surface area of a cold worked stainless steel article during the carburization
- chromium nitride precipitates in the surface area of a cold worked stainless steel article during the nitridation
- chromium carbide as well as chromium nitride precipitate in the surface area of a cold worked stainless steel article during the nitrocarburization.
- the free chromium content is reduced in the surface area of the cold worked and diffusion hardened stainless steel article, which significantly reduces its corrosion resistance.
- WO 2012/146254 A1 relates to a method for formation of expanded austenite and/or expanded martensite by solution hardening of a cold deformed workpiece of a passive alloy, which comprises a first step of dissolving at least nitrogen in the workpiece at a first temperature, which is higher than the solubility temperature for carbide and/or nitride and lower than the melting point of the passive alloy, and a subsequent second step of dissolving nitrogen and/or carbon in the workpiece at a second temperature, which is lower than the temperature at which carbides and/or nitrides form in the passive alloy.
- WO 2011/009463 A1 describes a method of activating an article of passive ferrous or non-ferrous metal, wherein the activation comprises the steps of i) heating the article to a first temperature, ii) heating at least one compound containing nitrogen and carbon to a second temperature for providing one or more gaseous species, and iii) contacting the article with the gaseous species, wherein the at least one compound containing nitrogen and carbon comprises at least four atoms.
- WO 2015/173380 A1 discloses a method of case hardening a workpiece made from a stainless steel comprising at least 9% chromium and up to 5% nickel, wherein the method comprises the steps of i) providing a workpiece punched from a sheet of the stainless steel, ii) optionally embossing the workpiece, iii) dissolving in an atmosphere of a nitrogen containing gas at least nitrogen in the workpiece at a first temperature, which is higher than the solubility temperature for nitride and lower than the melting point of the stainless steel, wherein dissolution of nitrogen at the first temperature is performed to obtain a diffusion depth of 10 ⁇ m to 50 ⁇ m with a content of nitrogen in the range of 0.05% to 0.5%, and iv) cooling the workpiece after the dissolution step to a second temperature which is lower than the temperature at which nitrides form in the stainless steel.
- US 2006/0070685 A1 refers to a process for producing a bearing component with an edge zone the process comprising the steps of i) providing an austenitic cold-rolled strip with a carbon content of 0.15-0.25% and a chromium alloying content of at least 12%; ii) initially deep-drawing the component from the strip; then enriching the strip at the edge zone with nitrogen as part of a heat treatment in a nitrogen-rich atmosphere; and iii) thereafter cooling the component to form a martensitic microstructure in which nitrogen is present in dissolved form.
- the object underlying the present invention is to provide a method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight, which leads to an article with an excellent surface hardness, a high hardness beneath the surface area of the article, an excellent yield strength, a high wear resistance as well as an excellent corrosion resistance.
- this object is satisfied by providing a method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight, comprising the steps of:
- the process in accordance with the present invention does not only lead to a high hardness of the article over its whole thickness as a consequence of the cold working as well as to an extremely high surface hardness as a consequence of the diffusion hardening, but in addition to an excellent wear resistance and corrosion resistance of the article on account of the annealing step.
- the articles obtained with the method in accordance with the present invention have a significantly increased surface hardness and an improved wear resistance.
- the articles obtained with the method in accordance with the present invention have an increased surface hardness, an improved hardness beneath the surface area of the article as well as an improved wear resistance.
- the articles obtained with the method in accordance with the present invention have an increased hardness beneath the surface area of the article as well as an improved wear resistance.
- the articles obtained with the method in accordance with the present invention have an increased corrosion resistance.
- Cold forming in the sense of the present patent application which is typically also called work hardening or strain hardening, is a method of strengthening a metal-article by plastic deformation. The strengthening occurs on account of dislocation movements and dislocation generation within the crystal structure of the material. Usually, cold forming is also used for shaping or forming the article, respectively, and is in general performed at a temperature below the full recrystallization temperature of the material, from which the article consists.
- the annealing step b) of the method in accordance with the present invention may be performed at any temperature between 450°C and 750°C and for any time between 5 minutes and 50 hours, as long as it is performed in a non-carburizing atmosphere, a non-nitriding atmosphere and a non-nitrocarburizing atmosphere, i.e. in an atmosphere which is non-carburizing atmosphere, non-nitriding and non-nitrocarburizing.
- the non-carburizing, non-nitriding and non-nitrocarburizing atmosphere contains no compound selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds.
- Nitrogen and/or carbon may be included in the atmosphere of step b), as long as step b) is performed at a temperature, at which the nitrogen and/or carbon is not diffused into the surface of the substrate. So the annealing step b) may be performed in a pure nitrogen atmosphere at a temperature below 850°C, since then no nitriding occurs.
- the temperature and duration of the annealing step b) slightly depends on the precise composition of the alloy, from which the article to be treated is made. Typically, the more severe the conditions during the annealing step, the more the hardness of the article decreases, but on the other hand the better the chromium containing precipitate generation is suppressed during the later diffusion hardening process.
- the annealing step b) is conducted for a duration and at a temperature selected from the aforementioned numeric value ranges so that the hardness of the cold worked article is not reduced in average by more than 15% during the annealing step b).
- the annealing step b) is preferably performed so that the hardness of the cold worked and annealed article is in average at least 85% of the hardness of the cold worked article before annealing.
- Hardness means in this connection the Vickers hardness.
- the annealing step b) is performed for a time of 5 minutes to 50 hours, preferably for 10 minutes to 20 hours and most preferably for 20 minutes to 10 hours.
- the annealing step b) of the method in accordance with the present invention is performed at a temperature between 550 and 700°C.
- the present invention is not particularly limited concerning the pressure, at which the annealing step b) is conducted.
- the annealing step b) may be performed at atmospheric pressure or under reduced pressure.
- the annealing step is performed in a non-carburizing atmosphere, a non-nitriding atmosphere and a non-nitrocarburizing atmosphere, i.e. in an atmosphere containing no compound selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds that would form diffusible compounds during the annealing step.
- a diffusion of carbon and/or nitrogen would occur during the annealing step b) at least to a small degree and this would initiate the formation of chromium containing precipitates, which would oppose the effects achieved with the method in accordance with the present invention.
- the effects of the annealing step b namely the reduction of chromium containing precipitates during the later diffusion hardening, are in a particular excellent extent obtained, when the annealing step b) is performed in an atmosphere which does not lead to a structural change of the surface, in particular to a change of the surface roughness and surface morphology of the article.
- the oxide layer of the article is maintained during the annealing step b).
- the annealing step b) is performed under vacuum, namely preferably at a pressure of at most 10.000 Pa and more preferably of at most 5.000 Pa.
- the annealing step b) is performed in an atmosphere, which also- i.e. in addition to diffusible compounds selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures thereof - does not include any compound, which would remove or even partially remove the oxide layer on the alloy, from which the article is made, during the annealing step b).
- the annealing step b) is performed in an atmosphere, which does not contain more than 5 % by volume of fluorine, of a fluorine containing compound and/or of a fluoride containing compound, preferably not more than 1 % by volume of fluorine, of a fluorine containing compound and/or of a fluoride containing compound, preferably not more than 0.1 % by volume of fluorine, of a fluorine containing compound and/or of a fluoride containing compound and most preferably no fluorine, no fluorine containing compound and no fluoride containing compound at all.
- the annealing step b) is performed in an atmosphere, which does not contain more than 5 % by volume of chlorine, of a chlorine containing compound and/or of a chloride containing compound, preferably not more than 1 % by volume of chlorine, of a chlorine containing compound and/or of a chloride containing compound, preferably not more than 0.1 % by volume of chlorine, of a chlorine containing compound and/or of a chloride containing compound and most preferably no chlorine, no chlorine containing compound and no chloride containing compound at all.
- the annealing step b) is performed in a reducing atmosphere, which assures that the oxide layer of the article is maintained during the annealing step b). Good results are in particular obtained, when the annealing step b) is performed in an atmosphere containing hydrogen.
- At least the surface region of the article is made of an alloy selected from the group consisting of stainless steel and nickel base alloys with a chromium content of at least 10 % by weight. However, it is preferred that the whole article consists completely of the alloy.
- step a) consists of austenitic stainless steel and/or duplex stainless steel.
- the thickness of the article there is no limitation concerning the thickness of the article and surprisingly good results are even obtained with comparable thick articles, which may be not processed for example with a method of the prior art comprising a solution nitriding treatment of the cold worked article before subjecting it to the diffusion hardening process.
- the method in accordance with the present invention is suitable for articles having a thickness of at least 100 ⁇ m and even for articles having a thickness of at least 5 mm.
- the cold forming for obtaining the article provided in step a) may be any cold forming step known to a person skilled in the art.
- the step a) may comprise plastically deforming the article at a temperature of at most 300°C, preferably by a technique selected from the group consisting of forging, extrusion, shaping, drawing, pressing, roll burnishing, rolling and combinations of two or more of the aforementioned techniques.
- step a) may comprise the machining of the article at a temperature of at most 200°C, preferably by a technique selected from the group consisting of turning, milling, punching, grinding, polishing and combinations of two or more of the aforementioned techniques.
- step a) comprises plastically deforming the article at a temperature of at most 300°C and machining the article at a temperature of at most 200°C, wherein the plastically deforming is preferably performed by a technique selected from the group consisting of forging, extrusion, shaping, drawing, pressing, roll burnishing, rolling and combinations of two or more of the aforementioned techniques and wherein the machining preferably performed by a technique selected from the group consisting of turning, milling, punching, grinding, polishing and combinations of two or more of the aforementioned techniques.
- the heat treatment in step d) is performed as carburizing step in a gaseous atmosphere comprising a carbon containing compound.
- the carbon containing compound is selected form the group consisting carbon monoxide, carbon dioxide, mixtures of carbon monoxide and carbon dioxide, hydrocarbon compounds and mixtures of two or more of the aforementioned compounds, wherein the hydrocarbon compound is preferably selected from the group consisting of C 1-6 -alkanes, fluorinated C 1-6 -alkanes, C 1-6 -alkenes, fluorinated C 1-6 -alkenes, C 1-6 -alkynes, fluorinated C 1-6 -alkynes and mixtures of two or more of the aforementioned compounds, wherein C 1-6 -alkynes and/or fluorinated C 1-6 -alkynes are particularly preferred.
- the aforementioned carburization gas may further comprise hydrogen, which promotes the decomposition of the carbon containing compound and thus the formation of diffusible carbon.
- the carburization gas may contain an inert gas, such as argon, as diluent.
- the heat treatment in step d) is performed as nitriding step in a gaseous atmosphere comprising a nitrogen containing compound.
- a nitrogen containing compound is ammonia and/or urea.
- the aforementioned nitriding gas may further comprise hydrogen, in order to promote the decomposition of the nitrogen containing compound and thus the formation of diffusible nitrogen, and/or an inert gas, such as argon, as diluent.
- the heat treatment in step d) is performed as nitrocarburization step in a gaseous atmosphere comprising a carbon containing compound as well as a nitrogen containing compound.
- a gaseous atmosphere comprising i) carbon monoxide, carbon dioxide, a mixture of carbon monoxide and carbon dioxide and/or a hydrocarbon compound, wherein the hydrocarbon compound is preferably selected from the group consisting of C 1-6 -alkanes, fluorinated C 1-6 -alkanes, C 1-6 -alkenes, fluorinated C 1-6 -alkenes, C 1-6 -alkynes, fluorinated C 1-6 -alkynes and mixtures of two or more of the aforementioned compounds, and ii) a nitrogen containing compound, wherein the nitrogen containing compound is ammonia and/or urea.
- the aforementioned nitrocarburization gas may further comprise hydrogen, in order to promote the decomposition of the carbon containing compound and of the nitrogen containing compound and thus the formation of diffusible nitrogen and carbon, and/or an inert gas, such as argon, as diluent.
- an inert gas such as argon
- the diffusion hardening performed during the heat treatment in step d) is performed as so called low temperature diffusion hardening at a temperature between 350 and less than 550°C in plasma, in a salt bath or in a gaseous atmosphere to obtain a nitride, carburized and/or nitrocarburized diffusion zone in the surface area of the article.
- a temperature between 350 and 510°C is particularly good.
- the diffusion hardening is performed for 2 to 50 hours.
- the heat treatment in step d) is preferably performed at atmospheric or subatmospheric pressure between 500 and 10,000 MPa.
- the heat treatment of the article in step d) is performed in plasma.
- the plasma heat treatment step d) is performed in plasma at a pressure of 100 to 1.000 Pa for 10 minutes to 100 hours in a carburizing atmosphere, in a nitriding atmosphere or in a nitrocarburizing atmosphere at a temperature of 100 to 550°C.
- the atmosphere preferably comprises carbon monoxide, carbon dioxide, a hydrocarbon compound, such as in particular methane, or a mixture thereof.
- the preferably oxygen free atmosphere preferably comprises ammonia and/or urea.
- the preferably oxygen free atmosphere preferably comprises i) carbon monoxide, carbon dioxide, a hydrocarbon compound, such as in particular methane, or a mixture thereof and ii) ammonia and/or urea.
- the atmosphere may further contain an inert gas, such as argon, as diluent and/or hydrogen, in order to promote the decomposition of the carbon and/or nitrogen containing compound and thus the formation of diffusible carbon and/or nitrogen.
- an inert gas such as argon, as diluent and/or hydrogen
- the plasma heat treatment step d) is performed in plasma at a pressure of 100 to 1.000 Pa in a carburizing atmosphere, in a nitriding atmosphere or in a nitrocarburizing atmosphere at a temperature of 400 to 500°C.
- the plasma treatment not only a diffusion hardening is performed, but also an activation of the surface of the article, i.e. the removal of the oxide layer of the article, is achieved.
- the plasma treatment simultaneously fulfils the activation step c) and the diffusion hardening step d).
- the activation in step c) is preferably performed before the heat treatment step d) and by sputtering the annealed article obtained in step b) preferably in an atmosphere comprising argon, hydrogen, a rare gas, such as helium, or a mixture thereof.
- the sputter activation step may be performed at a temperature between 100 and 550°C and preferably at a temperature of 300 to 500°C for 10 minutes to 10 hours and preferably for 1 to 10 hours.
- the heat treatment of the article in step d) is performed in a salt bath.
- the heat treatment is performed for 1 to 100 hours in a molten salt bath including as carbon donor and nitrogen donor a cyanide salt, such as sodium cyanide and/or potassium cyanide.
- a cyanide salt such as sodium cyanide and/or potassium cyanide.
- potassium chloride and lithium chloride are included in the salt bath and more preferably also an activator compound selected from the group consisting of barium chloride, strontium chloride, magnesium chloride, calcium chloride and mixtures of two or more of the aforementioned salts.
- the salt bath treatment simultaneously fulfils the activation step c) and the diffusion hardening step d).
- the heat treatment of the article in step d) is performed in a gaseous atmosphere.
- the preferred temperature conditions, pressure conditions and gas compositions for carburization, nitridation and nitrocarburization have been described above.
- the activation in step c) is preferably performed before the heat treatment step d) in a gaseous atmosphere comprising a fluorine compound at a temperature of 250 to 500°C.
- the fluorine compound is selected from the group consisting of fluorine, NF 3 , BF 3 , CF 4 , HF, SF 6 , C 2 F 6 , WF 6 , CHF 3 , SiF 4 , C 1-6 -fluorinated alkanes, C 1-6 -fluorinated alkenes, C 1-6 -fluorinated alkynes and mixtures of two or more of the aforementioned compounds.
- Good results are in particular achieved in this embodiment, when the activation is performed at a temperature of 250 to 550°C and preferably of 350 to 500°C for of 0.5 to 50 hours and preferably 1 to 15 hours in a gaseous atmosphere including NF 3 and/or N 2 at atmospheric pressure.
- step c) it is also possible to perform the activation according to step c) simultaneously with the heat treatment of the article in a gaseous atmosphere according to step d) for instance by using specific carbon containing compounds which also function as carbon donor.
- Suitable carbon containing compounds therefor are unsaturated C 1-6 -hydrocarbon compounds, such as C 1-6 -alkenes and C 1-6 -alkynes, such as acetylene.
- Particularly suitable for this purpose are halogenates hydrocarbon compounds and in particular unsaturated halogenates hydrocarbon compounds, such as fluorinated C 1-6 -alkenes and fluorinated C 1-6 -alkynes.
- the method in accordance with the present invention does not comprise any heating to a temperature above 900°C, preferably does not comprise any heating to a temperature above 800°C, more preferably does not comprise any heating to a temperature above 750°C and most preferably does not comprise any heating to a temperature above 700°C.
- the method in accordance with the present invention consists of steps a) to d) and optionally a cooling step between steps b) and c) to a temperature between 0°C and 100°C and preferably to a temperature between 23°C and 60°C and/or a cooling step between steps c) and d) to a temperature between 0°C and 100°C and preferably to a temperature between 23°C and 60°C.
- the present invention refers to a surface hardened article obtainable by a method in accordance with claim 13.
- the surface hardened article obtainable by a method in accordance with the present invention is characterized in that it does not only have a high hardness over its whole thickness as a consequence of the cold working as well as an extremely high surface hardness as a consequence of the diffusion hardening, but in addition an excellent wear resistance and corrosion resistance of the article on account of the annealing step.
- the surface hardened article in accordance with the present invention has in average a Vickers hardness HV1 measured in accordance with ASTM E92-16 of at least 150 and/or a surface hardness HV0.05 measured in accordance with ASTM E92-16 of at least 500.
- the surface hardened article has in average a Vickers hardness HV1 of at least 200, more preferably of at least 210 and most preferably of at least 220.
- the surface hardened article in accordance with the present invention preferably has a surface hardness HV0.05 measured in accordance with ASTM E92-16 of at least 600, more preferably of at least 650 and most preferably of at least 675.
- the surface hardened article in accordance with the present invention has a corrosion resistance measured in accordance with DIN EN ISO 8442-1 of December 1997 of less than 15 pitting corrosion points per 20 cm 2 surface area, preferably of less than 5 pitting corrosion points per 20 cm 2 surface area and more preferably of less than 1 pitting corrosion points per 20 cm 2 surface area.
- a set of key lock washers was prepared from austenitic stainless steel AISI 316 by cold working. More specifically, key lock washers 2, each of which comprising a first side 3 with radial teeth 4 and an opposite cam-side 5 with cams 6, were prepared by fine blanking of the inner and outer diameter of each key lock washer and subsequently embossing the first side with radial teeth and the camside with a cold working tool.
- key lock washers were subjected to an annealing step, in which the key lock washers were heated for 1 hour at 700°C in a vacuum furnace in a vacuum of about 500 Pa. The heating-up was performed in the furnace with a rate of 50°C per minute.
- the furnace was purged with 100 liter argon gas, before the annealed key lock washers were activated and simultaneously carburized at 420°C for 20 hours in an atmosphere comprising 5%by volume of acetylene, 50%by volume of hydrogen and 45%by volume of nitrogen.
- the so obtained surface hardened key lock washers showed the following propertied: Surface hardened washers of the example Base material hardness 1) 222 ⁇ 11 HV1 Surface hardness 2) 690 to 890 HV0.05 Diffusion zone depth 3) 11 to 14 ⁇ m Evaluation of corrosion resistance 4) No Corrosion products are visible on the surface in an optical microscope at 100x magnification. Evaluation of corrosion resistance 5) Surface free form corrosion products (cf. fig. 2 ).
- a set of key lock washers was prepared and surface hardened as described in the example except that no annealing step was performed between the cold working and the carburization.
- the so obtained surface hardened key lock washers showed the following propertied: Surface hardened washers of the comparative example Base material hardness 1) 235 ⁇ 13 HV1 Surface hardness 2) 680 to 840 HV0.05 Diffusion zone depth 3) 12 to 14 ⁇ m Evaluation of corrosion resistance 4) Corrosion products are visible on the surface and pitting corrosion spots can be seen in an optical microscope at 100x magnification. Evaluation of corrosion resistance 5) Corrosion products are visible on the surface on the camside and the cutting edge on the inner diameter and the outer diamete (cf. fig. 3 ). 1) to 5) As described for the example
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Description
- The present invention relates to a method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight. Moreover, the present invention relates to a surface hardened cold deformed article obtainable with this method.
- Articles, such as metal articles made of steel or a nickel base alloy, are often shaped by means of cold deformation, such as extrusion or cold forging. Cold deformation is a method for strengthening a metal by plastic deformation, which is usually performed in the course of shaping an article at a temperature below the recrystallization temperature of the material, from which the article is made. Stainless steels, such as austenitic stainless steel, usually have an excellent corrosion resistance, toughness and weldability, but have a comparable low yield strength as well as a comparable low wear resistance. Cold forming improves the yield strength of such articles on account of structural changes, i.e. in particular changes of the microstructure, such as the formation of martensite and the like, in the steel occurring as consequence of the plastic deformation occurring during the cold working.
- In particular for improving the wear resistance and for increasing specifically the surface hardness of articles made of stainless steel and comparable alloys, such articles are often also diffusion hardened in addition to the cold working, by subjecting the articles to a heat treatment at a temperature of typically 350 to 510°C in an atmosphere comprising a chemical compound forming during the heat treatment a species, which diffuses into the surface of the articles and thus improves the characteristics of the articles. Most prominent diffusion hardening methods are carburizing, nitriding and nitrocarburizing. While carbon diffuses during carburization into the surface area of the article, nitrogen diffuses during nitriding, carbon and nitrogen diffuse during nitrocarburizing and boron diffuses during boriding into the surface area of the article. Carburization, for example, is performed by heat treating the article in an atmosphere containing for instance an alkane, such as propane, and optionally further including hydrogen at 500°C for 10 hours. The article has to be activated during or better before the carburization, in order to remove the oxide layer of the article, which would act during the carburization as barrier. Such an activation is usually performed in a fluorine compound containing atmosphere, such as in a gaseous atmosphere comprising NF3 at a temperature of 250 to 500°C, such as for instance described in
EP 0 678 589 A1 . - A major disadvantage of diffusion hardening cold worked articles made of stainless steel or comparable alloys is that as consequence of the microstructural changes of the stainless steel or alloy, respectively, occurred during the cold working, compounds consisting of the diffusion element and of chromium from the stainless steel or alloy, respectively, precipitate during the diffusion hardening. For instance, chromium carbide precipitates in the surface area of a cold worked stainless steel article during the carburization, chromium nitride precipitates in the surface area of a cold worked stainless steel article during the nitridation and chromium carbide as well as chromium nitride precipitate in the surface area of a cold worked stainless steel article during the nitrocarburization. On account of this, however, the free chromium content is reduced in the surface area of the cold worked and diffusion hardened stainless steel article, which significantly reduces its corrosion resistance.
- In order to overcome these disadvantages, it has been already proposed to use for such cases specific stainless steel alloys, which are less prone to the formation of chromium rich precipitates. However, these specific stainless steel alloys are quite expensive so that they can be used only for expensive special products. Apart from that, for certain applications only materials are admitted, which are not less prone to the formation of chromium rich precipitates. The admission of the specific stainless steel alloys for specific applications would last at least 5 to 10 years. Apart from that, these specific stainless steel alloys are not readily available.
- Furthermore, it was suggested to reduce the time and temperature of the diffusion hardening in order to limit the amount of chromium rich precipitate formed during the diffusion hardening process. However, this leads to only very thin diffusion hardened surface areas, which is for many applications inacceptable.
- Thirdly, it has been proposed to perform a solution annealing process with the cold worked article before subjecting it to the diffusion hardening process at a comparable high temperature of above 1.000°C. However, this process leads to a significant reduction of the mechanical strength and hardness, namely of the surface hardness as well as of the hardness beneath the surface area of the article, which is inacceptable for most applications.
- Finally, it has been suggested for this purpose for instance in
WO 2013/0159781 A1 -
WO 2012/146254 A1 relates to a method for formation of expanded austenite and/or expanded martensite by solution hardening of a cold deformed workpiece of a passive alloy, which comprises a first step of dissolving at least nitrogen in the workpiece at a first temperature, which is higher than the solubility temperature for carbide and/or nitride and lower than the melting point of the passive alloy, and a subsequent second step of dissolving nitrogen and/or carbon in the workpiece at a second temperature, which is lower than the temperature at which carbides and/or nitrides form in the passive alloy. -
WO 2011/009463 A1 describes a method of activating an article of passive ferrous or non-ferrous metal, wherein the activation comprises the steps of i) heating the article to a first temperature, ii) heating at least one compound containing nitrogen and carbon to a second temperature for providing one or more gaseous species, and iii) contacting the article with the gaseous species, wherein the at least one compound containing nitrogen and carbon comprises at least four atoms. -
WO 2015/173380 A1 discloses a method of case hardening a workpiece made from a stainless steel comprising at least 9% chromium and up to 5% nickel, wherein the method comprises the steps of i) providing a workpiece punched from a sheet of the stainless steel, ii) optionally embossing the workpiece, iii) dissolving in an atmosphere of a nitrogen containing gas at least nitrogen in the workpiece at a first temperature, which is higher than the solubility temperature for nitride and lower than the melting point of the stainless steel, wherein dissolution of nitrogen at the first temperature is performed to obtain a diffusion depth of 10 µm to 50 µm with a content of nitrogen in the range of 0.05% to 0.5%, and iv) cooling the workpiece after the dissolution step to a second temperature which is lower than the temperature at which nitrides form in the stainless steel. -
US 2006/0070685 A1 refers to a process for producing a bearing component with an edge zone the process comprising the steps of i) providing an austenitic cold-rolled strip with a carbon content of 0.15-0.25% and a chromium alloying content of at least 12%; ii) initially deep-drawing the component from the strip; then enriching the strip at the edge zone with nitrogen as part of a heat treatment in a nitrogen-rich atmosphere; and iii) thereafter cooling the component to form a martensitic microstructure in which nitrogen is present in dissolved form. - In view of all this, the object underlying the present invention is to provide a method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight, which leads to an article with an excellent surface hardness, a high hardness beneath the surface area of the article, an excellent yield strength, a high wear resistance as well as an excellent corrosion resistance.
- In accordance with the present invention this object is satisfied by providing a method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight, comprising the steps of:
- a) providing a cold deformed article, wherein at least the surface region of the article is made of an alloy selected from the group consisting of stainless steel and nickel base alloys with a chromium content of at least 10 % by weight,
- b) annealing the cold deformed article for 5 minutes to 50 hours at a temperature between 450°C and 750°C in a non-carburizing atmosphere, a non-nitriding atmosphere and a non-nitrocarburizing atmosphere,
- c) activating the annealed article obtained in step b) and
- d) simultaneously with step c) or after step c) heat treating the annealed article at a temperature of 350 to less than 550°C for 2 to 50 hours in plasma, in a salt bath or in a gaseous atmosphere to obtain a nitride, carburized and/or nitrocarburized diffusion zone in the surface area of the article, wherein the plasma, the salt bath or the gaseous atmosphere contains a compound selected from the group consisting of carbon, nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds,
- This solution bases on the surprising finding that by performing an annealing step with the cold deformed article for 1 minute to 100 hours at a temperature between 100°C and 900°C, before subjecting the so treated article to an activation and low temperature diffusion hardening process, a precipitation of chromium rich agglomerates can be completely or at least to a great extent suppressed, even if the article has been cold formed. On account of this, the free chromium content of the alloy of the article and - as consequence thereof - also the corrosion resistance of the article in general and specifically of the surface area of the article is not reduced or, if at all, only insignificantly reduced. In contrast thereto, a respective method without performing the aforementioned annealing step would lead to the generation of significant amounts of chromium containing precipitates in the article leading to a significant reduction of the corrosion resistance of the article.
- In view of this, the process in accordance with the present invention does not only lead to a high hardness of the article over its whole thickness as a consequence of the cold working as well as to an extremely high surface hardness as a consequence of the diffusion hardening, but in addition to an excellent wear resistance and corrosion resistance of the article on account of the annealing step. In advantage to articles having been merely cold formed, the articles obtained with the method in accordance with the present invention have a significantly increased surface hardness and an improved wear resistance. Furthermore, in advantage to articles having been cold formed and solution annealed, before having been subjected to a diffusion hardening, the articles obtained with the method in accordance with the present invention have an increased surface hardness, an improved hardness beneath the surface area of the article as well as an improved wear resistance. In addition, in advantage to articles having been cold formed and subjected to solution nitriding treatment, before having been subjected to a diffusion hardening, the articles obtained with the method in accordance with the present invention have an increased hardness beneath the surface area of the article as well as an improved wear resistance. Finally, in advantage to articles having been cold formed and subjected to an activation and a low temperature diffusion hardening without annealing heat treatment there between, the articles obtained with the method in accordance with the present invention have an increased corrosion resistance.
- Cold forming in the sense of the present patent application, which is typically also called work hardening or strain hardening, is a method of strengthening a metal-article by plastic deformation. The strengthening occurs on account of dislocation movements and dislocation generation within the crystal structure of the material. Usually, cold forming is also used for shaping or forming the article, respectively, and is in general performed at a temperature below the full recrystallization temperature of the material, from which the article consists.
- Generally, the annealing step b) of the method in accordance with the present invention may be performed at any temperature between 450°C and 750°C and for any time between 5 minutes and 50 hours, as long as it is performed in a non-carburizing atmosphere, a non-nitriding atmosphere and a non-nitrocarburizing atmosphere, i.e. in an atmosphere which is non-carburizing atmosphere, non-nitriding and non-nitrocarburizing. Preferably, the non-carburizing, non-nitriding and non-nitrocarburizing atmosphere contains no compound selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds. Nitrogen and/or carbon may be included in the atmosphere of step b), as long as step b) is performed at a temperature, at which the nitrogen and/or carbon is not diffused into the surface of the substrate. So the annealing step b) may be performed in a pure nitrogen atmosphere at a temperature below 850°C, since then no nitriding occurs.
- Of course, the temperature and duration of the annealing step b) slightly depends on the precise composition of the alloy, from which the article to be treated is made. Typically, the more severe the conditions during the annealing step, the more the hardness of the article decreases, but on the other hand the better the chromium containing precipitate generation is suppressed during the later diffusion hardening process. According to a preferred embodiment of the present patent application, the annealing step b) is conducted for a duration and at a temperature selected from the aforementioned numeric value ranges so that the hardness of the cold worked article is not reduced in average by more than 15% during the annealing step b). In other words, the annealing step b) is preferably performed so that the hardness of the cold worked and annealed article is in average at least 85% of the hardness of the cold worked article before annealing. Hardness means in this connection the Vickers hardness.
- Taking the above into account, the annealing step b) is performed for a time of 5 minutes to 50 hours, preferably for 10 minutes to 20 hours and most preferably for 20 minutes to 10 hours.
- Good results are in particular obtained, if the annealing step b) of the method in accordance with the present invention is performed at a temperature between 550 and 700°C.
- Particular good results are obtained, when the annealing step b) of the method in accordance with the present invention is performed for 20 minutes to 10 hours at a temperature between 550°C and 700°C.
- The present invention is not particularly limited concerning the pressure, at which the annealing step b) is conducted. For instance, the annealing step b) may be performed at atmospheric pressure or under reduced pressure. As set out above, the annealing step is performed in a non-carburizing atmosphere, a non-nitriding atmosphere and a non-nitrocarburizing atmosphere, i.e. in an atmosphere containing no compound selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds that would form diffusible compounds during the annealing step. Otherwise, a diffusion of carbon and/or nitrogen would occur during the annealing step b) at least to a small degree and this would initiate the formation of chromium containing precipitates, which would oppose the effects achieved with the method in accordance with the present invention. Moreover, it has been found during the present invention that the effects of the annealing step b), namely the reduction of chromium containing precipitates during the later diffusion hardening, are in a particular excellent extent obtained, when the annealing step b) is performed in an atmosphere which does not lead to a structural change of the surface, in particular to a change of the surface roughness and surface morphology of the article. In particular, it is of advantage that the oxide layer of the article is maintained during the annealing step b).
- In view of this, it is preferred in accordance with a first preferred alternative of the present invention that the annealing step b) is performed under vacuum, namely preferably at a pressure of at most 10.000 Pa and more preferably of at most 5.000 Pa.
- Alternatively, it is preferred in accordance with a second preferred alternative of the present invention that the annealing step b) is performed in an atmosphere, which also- i.e. in addition to diffusible compounds selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures thereof - does not include any compound, which would remove or even partially remove the oxide layer on the alloy, from which the article is made, during the annealing step b). Accordingly, it is preferred in this second alternative that the annealing step b) is performed in an atmosphere, which does not contain more than 5 % by volume of fluorine, of a fluorine containing compound and/or of a fluoride containing compound, preferably not more than 1 % by volume of fluorine, of a fluorine containing compound and/or of a fluoride containing compound, preferably not more than 0.1 % by volume of fluorine, of a fluorine containing compound and/or of a fluoride containing compound and most preferably no fluorine, no fluorine containing compound and no fluoride containing compound at all. On account of the same reasons it is preferred in this second alternative that the annealing step b) is performed in an atmosphere, which does not contain more than 5 % by volume of chlorine, of a chlorine containing compound and/or of a chloride containing compound, preferably not more than 1 % by volume of chlorine, of a chlorine containing compound and/or of a chloride containing compound, preferably not more than 0.1 % by volume of chlorine, of a chlorine containing compound and/or of a chloride containing compound and most preferably no chlorine, no chlorine containing compound and no chloride containing compound at all.
- In a further development of the aforementioned second alternative, it is suggested that the annealing step b) is performed in a reducing atmosphere, which assures that the oxide layer of the article is maintained during the annealing step b). Good results are in particular obtained, when the annealing step b) is performed in an atmosphere containing hydrogen.
- As set out above, at least the surface region of the article is made of an alloy selected from the group consisting of stainless steel and nickel base alloys with a chromium content of at least 10 % by weight. However, it is preferred that the whole article consists completely of the alloy.
- Good results are for example obtained, when the cold deformed article provided in step a) consists of austenitic stainless steel and/or duplex stainless steel.
- In accordance with the present invention there is no limitation concerning the thickness of the article and surprisingly good results are even obtained with comparable thick articles, which may be not processed for example with a method of the prior art comprising a solution nitriding treatment of the cold worked article before subjecting it to the diffusion hardening process. In particular, the method in accordance with the present invention is suitable for articles having a thickness of at least 100 µm and even for articles having a thickness of at least 5 mm.
- The cold forming for obtaining the article provided in step a) may be any cold forming step known to a person skilled in the art. Exemplarily, the step a) may comprise plastically deforming the article at a temperature of at most 300°C, preferably by a technique selected from the group consisting of forging, extrusion, shaping, drawing, pressing, roll burnishing, rolling and combinations of two or more of the aforementioned techniques.
- Alternatively thereto, step a) may comprise the machining of the article at a temperature of at most 200°C, preferably by a technique selected from the group consisting of turning, milling, punching, grinding, polishing and combinations of two or more of the aforementioned techniques.
- It is also possible that the two aforementioned cold forming techniques are combined, namely that step a) comprises plastically deforming the article at a temperature of at most 300°C and machining the article at a temperature of at most 200°C, wherein the plastically deforming is preferably performed by a technique selected from the group consisting of forging, extrusion, shaping, drawing, pressing, roll burnishing, rolling and combinations of two or more of the aforementioned techniques and wherein the machining preferably performed by a technique selected from the group consisting of turning, milling, punching, grinding, polishing and combinations of two or more of the aforementioned techniques.
- In accordance with a preferred embodiment of the present invention, the heat treatment in step d) is performed as carburizing step in a gaseous atmosphere comprising a carbon containing compound. Good results are in particular obtained, when the carbon containing compound is selected form the group consisting carbon monoxide, carbon dioxide, mixtures of carbon monoxide and carbon dioxide, hydrocarbon compounds and mixtures of two or more of the aforementioned compounds, wherein the hydrocarbon compound is preferably selected from the group consisting of C1-6-alkanes, fluorinated C1-6-alkanes, C1-6-alkenes, fluorinated C1-6-alkenes, C1-6-alkynes, fluorinated C1-6-alkynes and mixtures of two or more of the aforementioned compounds, wherein C1-6-alkynes and/or fluorinated C1-6-alkynes are particularly preferred.
- Optionally, the aforementioned carburization gas may further comprise hydrogen, which promotes the decomposition of the carbon containing compound and thus the formation of diffusible carbon.
- Independently, from whether the carburization gas contains the optional hydrogen or not, the carburization gas may contain an inert gas, such as argon, as diluent.
- In accordance with an alternatively preferred embodiment of the present invention, the heat treatment in step d) is performed as nitriding step in a gaseous atmosphere comprising a nitrogen containing compound. Good results are in particular obtained, when the nitrogen containing compound is ammonia and/or urea. Optionally, the aforementioned nitriding gas may further comprise hydrogen, in order to promote the decomposition of the nitrogen containing compound and thus the formation of diffusible nitrogen, and/or an inert gas, such as argon, as diluent.
- In accordance with yet an alternatively preferred embodiment of the present invention, the heat treatment in step d) is performed as nitrocarburization step in a gaseous atmosphere comprising a carbon containing compound as well as a nitrogen containing compound. Good results are in particular obtained, when the nitrocarburization is performed in a gaseous atmosphere comprising i) carbon monoxide, carbon dioxide, a mixture of carbon monoxide and carbon dioxide and/or a hydrocarbon compound, wherein the hydrocarbon compound is preferably selected from the group consisting of C1-6-alkanes, fluorinated C1-6-alkanes, C1-6-alkenes, fluorinated C1-6-alkenes, C1-6-alkynes, fluorinated C1-6-alkynes and mixtures of two or more of the aforementioned compounds, and ii) a nitrogen containing compound, wherein the nitrogen containing compound is ammonia and/or urea. Optionally, the aforementioned nitrocarburization gas may further comprise hydrogen, in order to promote the decomposition of the carbon containing compound and of the nitrogen containing compound and thus the formation of diffusible nitrogen and carbon, and/or an inert gas, such as argon, as diluent.
- In accordance with the present invention, the diffusion hardening performed during the heat treatment in step d) is performed as so called low temperature diffusion hardening at a temperature between 350 and less than 550°C in plasma, in a salt bath or in a gaseous atmosphere to obtain a nitride, carburized and/or nitrocarburized diffusion zone in the surface area of the article. Particular good results are obtained, when the diffusion hardening is conducted at a temperature between 350 and 510°C.
- In accordance with the present invention, the diffusion hardening is performed for 2 to 50 hours.
- The heat treatment in step d) is preferably performed at atmospheric or subatmospheric pressure between 500 and 10,000 MPa.
- In accordance with a further preferred embodiment of the present invention, the heat treatment of the article in step d) is performed in plasma. Preferably, the plasma heat treatment step d) is performed in plasma at a pressure of 100 to 1.000 Pa for 10 minutes to 100 hours in a carburizing atmosphere, in a nitriding atmosphere or in a nitrocarburizing atmosphere at a temperature of 100 to 550°C.
- If a carburizing atmosphere is used, the atmosphere preferably comprises carbon monoxide, carbon dioxide, a hydrocarbon compound, such as in particular methane, or a mixture thereof. If a nitriding atmosphere is used, the preferably oxygen free atmosphere preferably comprises ammonia and/or urea. If a nitrocarburizing atmosphere is used, the preferably oxygen free atmosphere preferably comprises i) carbon monoxide, carbon dioxide, a hydrocarbon compound, such as in particular methane, or a mixture thereof and ii) ammonia and/or urea. Independently, from whether a carburizing atmosphere, a nitriding atmosphere or a nitrocarburizing atmosphere is used, the atmosphere may further contain an inert gas, such as argon, as diluent and/or hydrogen, in order to promote the decomposition of the carbon and/or nitrogen containing compound and thus the formation of diffusible carbon and/or nitrogen.
- Particular good results are obtained, when the plasma heat treatment step d) is performed in plasma at a pressure of 100 to 1.000 Pa in a carburizing atmosphere, in a nitriding atmosphere or in a nitrocarburizing atmosphere at a temperature of 400 to 500°C.
- During the plasma treatment not only a diffusion hardening is performed, but also an activation of the surface of the article, i.e. the removal of the oxide layer of the article, is achieved. In other words, the plasma treatment simultaneously fulfils the activation step c) and the diffusion hardening step d). However, in order to improve the activation efficiency, the activation in step c) is preferably performed before the heat treatment step d) and by sputtering the annealed article obtained in step b) preferably in an atmosphere comprising argon, hydrogen, a rare gas, such as helium, or a mixture thereof. The sputter activation step may be performed at a temperature between 100 and 550°C and preferably at a temperature of 300 to 500°C for 10 minutes to 10 hours and preferably for 1 to 10 hours.
- In accordance with a further preferred embodiment of the present invention, the heat treatment of the article in step d) is performed in a salt bath. Preferably, the heat treatment is performed for 1 to 100 hours in a molten salt bath including as carbon donor and nitrogen donor a cyanide salt, such as sodium cyanide and/or potassium cyanide. In addition to the cyanide salt, preferably potassium chloride and lithium chloride are included in the salt bath and more preferably also an activator compound selected from the group consisting of barium chloride, strontium chloride, magnesium chloride, calcium chloride and mixtures of two or more of the aforementioned salts.
- Particular good results are obtained, when the salt bath heat treatment step d) is performed in a salt bath at a temperature of 350 to 410°C.
- During the treatment in the salt bath containing cyanide salt(s) not only a diffusion hardening is performed, but also an activation of the surface of the article, i.e. the removal of the oxide layer of the article, is achieved. In other words, the salt bath treatment simultaneously fulfils the activation step c) and the diffusion hardening step d).
- In accordance with a further preferred embodiment of the present invention, the heat treatment of the article in step d) is performed in a gaseous atmosphere. The preferred temperature conditions, pressure conditions and gas compositions for carburization, nitridation and nitrocarburization have been described above. In this embodiment, the activation in step c) is preferably performed before the heat treatment step d) in a gaseous atmosphere comprising a fluorine compound at a temperature of 250 to 500°C. Preferably, the fluorine compound is selected from the group consisting of fluorine, NF3, BF3, CF4, HF, SF6, C2F6, WF6, CHF3, SiF4, C1-6-fluorinated alkanes, C1-6-fluorinated alkenes, C1-6-fluorinated alkynes and mixtures of two or more of the aforementioned compounds. Good results are in particular achieved in this embodiment, when the activation is performed at a temperature of 250 to 550°C and preferably of 350 to 500°C for of 0.5 to 50 hours and preferably 1 to 15 hours in a gaseous atmosphere including NF3 and/or N2 at atmospheric pressure.
- Alternatively to the aforementioned embodiment, it is also possible to perform the activation according to step c) simultaneously with the heat treatment of the article in a gaseous atmosphere according to step d) for instance by using specific carbon containing compounds which also function as carbon donor. Suitable carbon containing compounds therefor are unsaturated C1-6-hydrocarbon compounds, such as C1-6-alkenes and C1-6-alkynes, such as acetylene. Particularly suitable for this purpose are halogenates hydrocarbon compounds and in particular unsaturated halogenates hydrocarbon compounds, such as fluorinated C1-6-alkenes and fluorinated C1-6-alkynes.
- In order to reliably avoid a generation of chromium containing precipitates in the finally treated article, it is in a further development of the idea of the present invention as most preferably suggested that the method in accordance with the present invention does not comprise any heating to a temperature above 900°C, preferably does not comprise any heating to a temperature above 800°C, more preferably does not comprise any heating to a temperature above 750°C and most preferably does not comprise any heating to a temperature above 700°C.
- Due to the same reasons, it is particularly preferred that the method in accordance with the present invention consists of steps a) to d) and optionally a cooling step between steps b) and c) to a temperature between 0°C and 100°C and preferably to a temperature between 23°C and 60°C and/or a cooling step between steps c) and d) to a temperature between 0°C and 100°C and preferably to a temperature between 23°C and 60°C.
- In addition, the present invention refers to a surface hardened article obtainable by a method in accordance with claim 13.
- As set out above, the surface hardened article obtainable by a method in accordance with the present invention is characterized in that it does not only have a high hardness over its whole thickness as a consequence of the cold working as well as an extremely high surface hardness as a consequence of the diffusion hardening, but in addition an excellent wear resistance and corrosion resistance of the article on account of the annealing step.
- More specifically, the surface hardened article in accordance with the present invention has in average a Vickers hardness HV1 measured in accordance with ASTM E92-16 of at least 150 and/or a surface hardness HV0.05 measured in accordance with ASTM E92-16 of at least 500. Preferably, the surface hardened article has in average a Vickers hardness HV1 of at least 200, more preferably of at least 210 and most preferably of at least 220.
- In addition, the surface hardened article in accordance with the present invention preferably has a surface hardness HV0.05 measured in accordance with ASTM E92-16 of at least 600, more preferably of at least 650 and most preferably of at least 675.
- Furthermore, the surface hardened article in accordance with the present invention has a corrosion resistance measured in accordance with DIN EN ISO 8442-1 of December 1997 of less than 15 pitting corrosion points per 20 cm2 surface area, preferably of less than 5 pitting corrosion points per 20 cm2 surface area and more preferably of less than 1 pitting corrosion points per 20 cm2 surface area.
- Subsequently, the present invention is described by reference to an example and a comparative example, which, however, do not limit the scope of the present invention.
- First of all, a set of key lock washers was prepared from austenitic stainless steel AISI 316 by cold working. More specifically,
key lock washers 2, each of which comprising afirst side 3 withradial teeth 4 and an opposite cam-side 5 withcams 6, were prepared by fine blanking of the inner and outer diameter of each key lock washer and subsequently embossing the first side with radial teeth and the camside with a cold working tool. - Afterwards, so produced key lock washers were subjected to an annealing step, in which the key lock washers were heated for 1 hour at 700°C in a vacuum furnace in a vacuum of about 500 Pa. The heating-up was performed in the furnace with a rate of 50°C per minute.
- Subsequently, the furnace was purged with 100 liter argon gas, before the annealed key lock washers were activated and simultaneously carburized at 420°C for 20 hours in an atmosphere comprising 5%by volume of acetylene, 50%by volume of hydrogen and 45%by volume of nitrogen.
- The so obtained surface hardened key lock washers showed the following propertied:
Surface hardened washers of the example Base material hardness 1) 222 ± 11 HV1 Surface hardness 2) 690 to 890 HV0.05 Diffusion zone depth 3) 11 to 14 µm Evaluation of corrosion resistance 4) No Corrosion products are visible on the surface in an optical microscope at 100x magnification. Evaluation of corrosion resistance 5) Surface free form corrosion products (cf. fig. 2 ).1) Measured in accordance with ASTM E92-16 2) Measured in accordance with ASTM E92-16 3) Determined in in dependence on DIN EN ISO 1463, 2004 with a Kalling II etchant at 1000x magnification 4) Determined in accordance with the Test described in EN ISO 8442-1, version of December 1997 5) Determined after immersion of the key lock washers for 68 hours in 200ml 3% NaCl for 68 hours at ambient temperature - A set of key lock washers was prepared and surface hardened as described in the example except that no annealing step was performed between the cold working and the carburization.
- The so obtained surface hardened key lock washers showed the following propertied:
Surface hardened washers of the comparative example Base material hardness 1) 235 ± 13 HV1 Surface hardness 2) 680 to 840 HV0.05 Diffusion zone depth 3) 12 to 14 µm Evaluation of corrosion resistance 4) Corrosion products are visible on the surface and pitting corrosion spots can be seen in an optical microscope at 100x magnification. Evaluation of corrosion resistance 5) Corrosion products are visible on the surface on the camside and the cutting edge on the inner diameter and the outer diamete (cf. fig. 3 ).1) to 5) As described for the example -
- 1
- Set of key lock washers
- 2
- Key lock washer
- 3
- First side of Key lock washer
- 4
- Radial teeth of
Key lock washer 4 - 5
- Cam-side of Key lock washer
- 6
- Cams of Key lock washer
Claims (14)
- A method for surface hardening a cold deformed article at least partially consisting of stainless steel or a nickel base alloy with a chromium content of at least 10 % by weight, comprising the steps of:a) providing a cold deformed article, wherein at least the surface region of the article is made of an alloy selected from the group consisting of stainless steel and nickel base alloys with a chromium content of at least 10 % by weight,b) annealing the cold deformed article for 5 minutes to 50 hours at a temperature between 450°C and 750°C in a non-carburizing atmosphere, a non-nitriding atmosphere and a non-nitrocarburizing atmosphere,c) activating the annealed article obtained in step b) andd) simultaneously with step c) or after step c) heat treating the annealed article at a temperature of 350 to less than 550°C for 2 to 50 hours in plasma, in a salt bath or in a gaseous atmosphere to obtain a nitride, carburized and/or nitrocarburized diffusion zone in the surface area of the article, wherein the plasma, the salt bath or the gaseous atmosphere contains a compound selected from the group consisting of carbon, nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds,wherein the annealing in step b) is performed with a higher temperature than the heat treating in step d).
- The method in accordance with claim 1,
characterized in that
the annealing in step b) is performed in an atmosphere containing no compound selected from the group consisting of nitrogen containing compounds, carbon containing compounds and mixtures of two or more of the aforementioned compounds and preferably also no nitrogen and carbon. - The method in accordance with claim 1 or 2,
characterized in that
the annealing in step b) is performed at a temperature between 550 and 700°C. - The method in accordance with any of the preceding claims,
characterized in that
the annealing in step b) is performed under vacuum with a pressure of at most 10.000 Pa and preferably of at most 5.000 Pa or the annealing in step b) is performed in a reducing atmosphere, preferably an atmosphere containing hydrogen and more preferably an atmosphere consisting of hydrogen, at atmospheric pressure. - The method in accordance with any of the preceding claims,
characterized in that
the article consists of the alloy, wherein preferably the cold deformed article provided in step a) consists of austenitic stainless steel and/or duplex stainless steel and preferably has a thickness of at least 100 µm and preferably of at least 5 mm. - The method in accordance with any of the preceding claims,
characterized in thatstep a) comprises plastically deforming the article at a temperature of at most 300°C, preferably by a technique selected from the group consisting of forging, extrusion, shaping, drawing, pressing, roll burnishing, rolling and combinations of two or more of the aforementioned techniques, and/orstep a) comprises machining the article at a temperature of at most 200°C, preferably by a technique selected from the group consisting of turning, milling, punching, grinding, polishing and combinations of two or more of the aforementioned techniques,
and/orstep a) comprises plastically deforming the article at a temperature of at most 300°C and machining the article at a temperature of at most 200°C, wherein the plastically deforming is preferably performed by a technique selected from the group consisting of forging, extrusion, shaping, drawing, pressing, roll burnishing, rolling and combinations of two or more of the aforementioned techniques and wherein the machining preferably performed by a technique selected from the group consisting of turning, milling, punching, grinding, polishing and combinations of two or more of the aforementioned techniques. - The method in accordance with any of the preceding claims,
characterized in that
the heat treatment in step d) is performed as carburizing in a gaseous atmosphere comprising a compound selected form the group consisting carbon monoxide, carbon dioxide, mixtures of carbon monoxide and carbon dioxide, hydrocarbon compounds and mixtures of two or more of the aforementioned compounds, wherein the hydrocarbon compound is preferably selected from the group consisting of C1-6-alkanes, fluorinated C1-6-alkanes, C1-6-alkenes, fluorinated C1-6-alkenes, C1-6-alkynes, fluorinated C1-6-alkynes and mixtures of two or more of the aforementioned compounds, wherein the gaseous atmosphere preferably further comprises hydrogen. - The method in accordance with any of the preceding claims,
characterized in that
the heat treatment in step d) is performed as nitriding in a gaseous atmosphere comprising a nitrogen containing compound and optionally further comprising hydrogen, wherein the nitrogen containing compound is preferably ammonia and/or urea. - The method in accordance with any of the preceding claims,
characterized in that
the heat treatment in step d) is performed as nitrocarburization in a gaseous atmosphere comprising i) a compound selected from the group consisting of carbon monoxide, carbon dioxide, a mixture of carbon monoxide and carbon dioxide, hydrocarbon compounds and mixtures of two or more of the aforementioned compounds and ii) a nitrogen containing compound, wherein the hydrocarbon compound is preferably selected from the group consisting of C1-6-alkanes, fluorinated C1-6-alkanes, C1-6-alkenes, fluorinated C1-6-alkenes, C1-6-alkynes, fluorinated C1-6-alkynes and mixtures of two or more of the aforementioned compounds, and wherein the nitrogen containing compound is preferably ammonia and/or urea, wherein the gaseous atmosphere preferably further comprises hydrogen. - The method in accordance with any of the preceding claims,
characterized in that
the heat treatment in step d) is performed at a temperature between 350 and 510°C, wherein the heat treatment in step d) is preferably performed for 5 to 20 hours. - The method in accordance with any of the preceding claims,
characterized in that
the heat treatment of the article in step d) is performed in a gaseous atmosphere and the activation in step c) is performed by heat treating the article in a gaseous atmosphere comprising a fluorine compound at a temperature of 250 to 500°C, wherein the fluorine compound is preferably selected from the group consisting of fluorine, NF3, BF3, CF4, HF, SF , C2F , WF , CHF3, SiF4, C1-6-fluorinated alkanes, C1-6-fluorinated alkenes, C1-6-fluorinated alkynes and mixtures of two or more of the aforementioned compounds. - The method in accordance with any of the preceding claims,
characterized in that
the method does not comprise any heating to a temperature above 900°C, preferably does not comprise any heating to a temperature above 800°C, more preferably does not comprise any heating to a temperature above 750°C and most preferably does not comprise any heating to a temperature above 700°C. - A surface hardened article obtainable by a method in accordance with any of the preceding claims
characterized in thatit has a Vickers hardness HV1 measured in accordance with ASTM E92-16 of at least 150, preferably of at least 200, more preferably of at least 210 and most preferably of at least 220,
and/orit has a surface hardness HV0.05 measured in accordance with ASTM E92-16 of at least 500, preferably of at least 600, more preferably of at least 650 and most preferably of at least 675, andcharacterized in thatit has a corrosion resistance measured in accordance with DIN EN ISO 8442-1 of December 1997 of less than 15 pitting corrosion points per 20 cm2 surface area. - The surface hardened article in accordance with claim 13, which has a corrosion resistance measured in accordance with DIN EN ISO 8442-1 of December 1997 of less than 5 pitting corrosion points per 20 cm2 surface area and preferably of less than 1 pitting corrosion points per 20 cm2 surface area.
Priority Applications (2)
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CN108588635B (en) * | 2018-04-26 | 2020-09-29 | 台州市百达热处理有限公司 | Salt bath nitriding treatment method for high-speed steel sliding sheet of compressor |
CN109022730A (en) * | 2018-10-26 | 2018-12-18 | 重庆工业职业技术学院 | Austenite stainless steel surface S phase and anti-corrosion layer acquisition methods |
CN111020465A (en) * | 2019-12-23 | 2020-04-17 | 成都赛飞斯金属科技有限公司 | Surface treating agent for low-temperature salt bath nitrogen-carbon-oxygen co-cementation technology and using method |
CN112375884B (en) * | 2020-11-19 | 2022-09-27 | 河南中原特钢装备制造有限公司 | Forging method for refining steel grains and reducing hydrogen content in steel |
CN113817979B (en) * | 2021-09-23 | 2022-08-23 | 东北大学 | Method for preparing ultra-thick nitriding/carbon layer through permeation-annealing cycle |
CN114107883B (en) * | 2021-11-29 | 2024-01-12 | 上海航天设备制造总厂有限公司 | Local ion nitriding method for inner cavity of precipitation hardening stainless steel annular part |
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EP3299487A1 (en) | 2018-03-28 |
DK3299487T4 (en) | 2023-01-30 |
DK3299487T3 (en) | 2020-03-30 |
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