WO2023114498A1 - Articles fabricated from cold-worked and case-hardened essentially co-free stainless steel alloys and methods of fabrication thereof - Google Patents

Articles fabricated from cold-worked and case-hardened essentially co-free stainless steel alloys and methods of fabrication thereof Download PDF

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Publication number
WO2023114498A1
WO2023114498A1 PCT/US2022/053218 US2022053218W WO2023114498A1 WO 2023114498 A1 WO2023114498 A1 WO 2023114498A1 US 2022053218 W US2022053218 W US 2022053218W WO 2023114498 A1 WO2023114498 A1 WO 2023114498A1
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Prior art keywords
stainless steel
article
nitrogen
surface layer
carbon
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PCT/US2022/053218
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English (en)
French (fr)
Inventor
Stephane Alexis Jacques FORSIK
Mario Epler
Alojz Kajinic
Gaurav LALWANI
Logan SMITH
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Carpenter Technology Corp
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Carpenter Technology Corp
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Application filed by Carpenter Technology Corp filed Critical Carpenter Technology Corp
Priority to KR1020247023833A priority Critical patent/KR20240128007A/ko
Priority to EP22850848.7A priority patent/EP4448808A1/en
Priority to JP2024535865A priority patent/JP7902938B2/ja
Publication of WO2023114498A1 publication Critical patent/WO2023114498A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/12—Both compacting and sintering
    • B22F3/14—Both compacting and sintering simultaneously
    • B22F3/15—Hot isostatic pressing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/17—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by forging
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • 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
    • 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
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • 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
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • 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
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/007—Heat treatment of ferrous alloys containing Co
    • 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
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D9/22—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for drills; for milling cutters; for machine cutting tools
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
    • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
    • 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
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/28—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases more than one element being applied in one step
    • C23C8/30—Carbo-nitriding
    • C23C8/32—Carbo-nitriding of ferrous surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/18—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by using pressure rollers
    • B22F2003/185—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by using pressure rollers by hot rolling, below sintering temperature
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • B22F2003/248—Thermal after-treatment
    • 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

Definitions

  • Embodiments of the invention relate to a method of processing essentially cobalt-free wrought stainless steels and articles of manufacture made therefrom. More particularly, certain embodiments of the invention relate to the processing of stainless steels to increase their strength and create a hardened surface that offers improved resistance to wear, corrosion, and fatigue. Certain articles processed according to various embodiments of the invention are suitable for medical load-bearing applications such as articulating orthopedic implants.
  • CoCrMo or CCM cobalt-chromium-molybdenum alloys
  • CCM cobalt-chromium-molybdenum alloys
  • CoCrMo alloys with 27-30 wt.% of chromium and 5-7 wt.% of molybdenum are used either in the cast (ASTM F75) or wrought (ASTM F1237) condition.
  • Other CoCrMo alloys with different ratios of cobalt/chromium/molybdenum are used in the wrought condition (see e.g., specifications ASTM F90, F562, F799, F1537).
  • Stainless steels have an iron base and additions of chromium, nickel, and molybdenum (ASTM F138) or additions of chromium, nickel, manganese, molybdenum, and nitrogen (ASTM F1586) and are used in the wrought condition.
  • ASTM F138 iron base and additions of chromium, nickel, and molybdenum
  • ASTM F1586 additions of chromium, nickel, manganese, molybdenum, and nitrogen
  • ASTM standard F2229 -21 Standard Specification for Wrought, Nitrogen Strengthened 23Manganese-21 Chromium - 1 Molybdenum Low -Nickel Stainless Steel Alloy Bar and Wire for Surgical Implants (referred to herein as “ASTM F2229 stainless steel”), which is hereby incorporated by reference in its entirety, for all purposes.
  • ASTM F2229 stainless steel Nitrogen Strengthened 23Manganese-21 Chromium - 1 Molybdenum Low -Nickel Stainless Steel Alloy Bar and Wire for Surgical Implants
  • ASTM F2229 stainless steel Nitrogen Strengthened 23Manganese-21 Chromium - 1 Molybdenum Low -Nickel Stainless Steel Alloy Bar and Wire for Surgical Implants
  • ASTM standard F1586-21 Standard Specification for Wrought Nitrogen Strengthened 21 Chromium- 10Nickel-3Manganese- 2.5Molybdenum Stainless Steel Alloy Bar for Surgical Implants (UNS S31675), referred to herein as “ASTM F1586 stainless steel”, which is hereby incorporated by reference in its entirety, for all purposes.
  • ASTM F1586 stainless steel This alloy is discussed in US9695505B2 and US9387022B2.
  • An example of a material that complies with the standard is BioDur® 734 stainless steel, available from Carpenter Technology Corporation (USA).
  • HNHC stainless steel high nitrogen, high chromium stainless steel
  • ASM SS-1231 such as Micro-Melt® NCORRTM stainless steel, available from Carpenter Technology Corporation (USA).
  • Embodiments of the invention may be used in various applications, such as for fabrication of articulating orthopedic implants.
  • properties required for the articulating surface significantly differ from those required for the bulk of the material as the articulating surface is preferably wear resistant and at the same time have excellent fatigue, corrosion and tribocorrosion properties.
  • the bulk of the alloy has its own requirements in terms of Young’s modulus of elasticity, fracture toughness, etc.
  • alloys for articulating orthopedic applications are preferably specifically processed for the surface of the material to be significantly much harder than the bulk of the material.
  • the processes described herein may also be used to provide articles for other applications, such as watch components, electrical components, or drilling components, i.e., any applications that require a hard, wear resistant surface in combination with bulk properties provided by ASTM F2229 stainless steel, ASTM F1586 stainless steel or high nitrogen, high chromium stainless steel (“HNHC stainless steel”) such as the material described in U.S. Patent No. 6,168,755.
  • ASTM F2229 stainless steel ASTM F1586 stainless steel or high nitrogen, high chromium stainless steel
  • HNHC stainless steel high chromium stainless steel
  • embodiments of the invention relate to a method for fabricating an article.
  • the method includes the steps of: forming a billet including or consisting essentially of a stainless steel composition of manganese 2.00 wt.% - 24.00 wt.%, chromium 19.00 wt.% - 30 wt.%, molybdenum 0.50 wt.% - 4.0 wt.%, nitrogen 0.25 wt.% - 1.10 wt.%, carbon ⁇ 1 wt.%, phosphorus ⁇ 0.03 wt.%, sulfur ⁇ 1 wt.%, nickel ⁇ 22 wt.%, cobalt ⁇ 0.10 wt.%, silicon ⁇ 1 wt.%, niobium ⁇ 0.80 wt.%, oxygen ⁇ 1 wt.%, copper ⁇ 0.25 wt.%, balance iron; annealing the billet; cold working the billet to form the article; and without annealing of the article
  • the stainless steel composition may include: manganese 21.00 wt.% - 24.00 wt.%, chromium 19.00 wt.% - 23.00 wt.%, molybdenum 0.50 wt.% - 1.50 wt.%, nitrogen 0.85 wt.% - 1.10 wt.%, carbon ⁇ 0.08 wt.%, phosphorus ⁇ 0.03 wt.%, sulfur ⁇ 0.01 wt.%, nickel ⁇ 0.05 wt.%, cobalt ⁇ 0.1 wt.%, silicon ⁇ 0.75 wt.%, niobium 0 wt.%, copper ⁇ 0.25 wt.%, balance iron.
  • the stainless steel composition may include: manganese 2.00 wt.% - 4.25 wt.%, chromium 19.5 wt.% - 22.0 wt.%, molybdenum 2.0 wt.% - 3.0 wt.%, nitrogen 0.25 wt.% - 0.50 wt.%, carbon ⁇ 0.08 wt.%, phosphorus ⁇ 0.025 wt.%, sulfur ⁇ 0.01 wt.%, nickel 9.0 wt.% - 11.0 wt.%, cobalt ⁇ 0.10 wt%, silicon ⁇ 0.75 wt.%, niobium 0.25 wt.% - 0.80 wt.%, copper ⁇ 0.25 wt.%, balance iron.
  • the stainless steel composition may include: manganese 5.85 wt.% - 15 wt.%, chromium 27 wt.% - 30 wt.%, molybdenum 1.5 wt.% - 4.0 wt.%, nitrogen 0.8 wt.% - 0.97 wt.%, phosphorus ⁇ 0.02 wt.%, nickel 8 wt.% - 22 wt.%, cobalt ⁇ 0.01 wt.%, silicon, oxygen, carbon, and sulfur such that (silicon + oxygen + carbon + sulfur ) ⁇ 1 wt.%, niobium 0 wt.%, copper ⁇ 0.01 wt.%, balance iron.
  • Forming the billet may include melting and remelting an ingot under air, vacuum or slag and forging the ingot to make a billet.
  • Forming the billet may include forming a powder comprising the stainless steel composition; and pressing the powder to form the billet.
  • Cold working the billet may include at least one of cold forming, cold rolling, cold drawing, shot peening, or pilgering.
  • the case hardening may be performed at a single temperature selected from a range of 400 °C - 1000 °C (752 °F - 1832 °F).
  • the case hardening may be performed for a duration selected from a range of 1 hour to 16 hours.
  • Case hardening may include boriding, carburizing, nitriding, carbonitriding, and/or a combination thereof.
  • the surface layer may include a surface hardness of at least 350 HV.
  • the surface layer may include the billet stainless steel composition and further include at least one of carbon, nitrogen, boron, or a combination diffused therein.
  • the article may include an articulating orthopedic device element, a watch component, an electrical component, or a drilling component.
  • inventions of the invention relate to an articulating orthopedic device.
  • the articulating orthopedic device may include: a first element comprising a first articular surface; and a second element including a second articular surface configured to articulate with the first articular surface, the first and second elements each consisting essentially of a stainless steel composition of manganese 2.00 wt.% - 24.00 wt.%, chromium 19.00 wt.% - 30 wt.%, molybdenum 0.50 wt.% - 4.00 wt.%, nitrogen 0.25 wt.% - 1.10 wt.%, carbon ⁇ 1 wt.%, phosphorus ⁇ 0.03 wt.%, sulfur ⁇ 1 wt.%, nickel ⁇ 22.00 wt.%, cobalt ⁇ 0.
  • the first and second articular surfaces each include a surface layer including or consisting essentially of the stainless steel composition and further including at least one of carbon, nitrogen, or boron diffused therein.
  • the surface layer may have a surface hardness of at least 350 HV.
  • the articulating orthopedic device may further include an acetabular cup disposed between the first and second elements.
  • the acetabular cup may include a metal, a ceramic, and/or a polymer.
  • embodiments of the invention relate to a stainless steel article.
  • the stainless steel article includes a bulk material having at least one of a hardness of at least 300 HV or a yield strength of at least 145 ksi and consisting essentially of a stainless steel composition of manganese 2.00 wt.% - 24.00 wt.%, chromium 19.00 wt.% - 30 wt.%, molybdenum 0.50 wt.% - 4.00 wt.%, nitrogen 0.25 wt.% - 1.10 wt.%, carbon ⁇ 1 wt.%, phosphorus ⁇ 0.03 wt.%, sulfur ⁇ 1 wt.%, nickel ⁇ 22.00 wt.%, cobalt ⁇ 0.10 wt.%, silicon ⁇ 1 wt.%, niobium ⁇ 0.80 wt.%, oxygen ⁇ 1 wt.%, copper ⁇ 0.25 wt.%, balance iron; and a surface layer disposed on the bulk material.
  • the surface layer includes
  • the surface layer may have a thickness selected from a range of 10 micrometers to 1000 micrometers, or a range of 30 micrometers to 40 micrometers.
  • a carbon concentration may range from at least 0.10 wt.% at atop surface of the surface layer to ⁇ 0.08 wt.% in bulk material.
  • a nitrogen concentration may range from at least 1.10 wt.% at a top surface of the surface layer to a range of 0.85 wt.% to 1.10 wt.% N in the bulk material, and the nitrogen concentration in the surface layer may be higher than in the bulk material.
  • a boron concentration may range from at least 0.10 wt.% at a top surface of the surface layer to 0 wt.% in the bulk material.
  • the stainless steel article may be an articulating orthopedic device element, a watch component, an electrical component, or a drilling component.
  • Figure 1 is a chart of the yield strength (YS) and ultimate tensile strength (UTS) of ASTM F2229 stainless steel such as BioDur® 108 stainless steel as a function of the percent of cold working.
  • Figure 2 is a chart of the YS and UTS of ASTM F1586 stainless steel such as BioDur® 734 stainless steel as a function of the percent of cold working.
  • Figure 3 is a chart of the YS and UTS of high nitrogen, high chromium stainless steel (“HNHC stainless steel”) such as ASM SS-1231 stainless steel as a function of the percent of cold working.
  • HNHC stainless steel high nitrogen, high chromium stainless steel
  • Figure 4 is a schematic representation of a case hardening process.
  • Figure 5 is a schematic representation of an artificial hip joint.
  • Figure 6A is a graph illustrating hardness versus distance from a surface of BioDur® 108 stainless steel samples processed in accordance with embodiments of the invention.
  • Figure 6B is a graph illustrating the carbon concentration in wt.% versus distance from a surface of BioDur® 108 stainless steel samples processed in accordance with embodiments of the invention.
  • Figure 6C is a series of micrographs of the samples of Figure 6A and Figure 6B.
  • Figure 7A is a graph illustrating hardness versus distance from a surface of BioDur® 734 stainless steel samples processed in accordance with embodiments of the invention.
  • Figure 7B is a graph illustrating the carbon concentration in wt.% versus distance from a surface of BioDur® 734 stainless steel samples processed in accordance with embodiments of the invention.
  • Figure 7C is a series of micrographs of the samples of Figure 7A and Figure 7B.
  • Figure 8A is a graph illustrating hardness versus distance from a surface of NCORRTM stainless steel samples processed in accordance with embodiments of the invention.
  • Figure 8B is a graph illustrating the carbon concentration in wt.% versus distance from a surface of NCORRTM stainless steel samples processed in accordance with embodiments of the invention.
  • Figure 8C is a series of micrographs of the samples of Figure 8A and Figure 8B. Detailed Description
  • Processes in accordance with embodiments of the invention modify stainless steel alloys that comply with (i) the ASTM F2229 stainless steel composition, e.g., commercially available BioDur® 108 stainless steel, (ii) the ASTM F1586 stainless steel composition, e.g., commercially available BioDur® 734 stainless steel, or (iii) high nitrogen, high chromium stainless steel (“HNHC stainless steel”), e.g., as described in U.S. Patent No.
  • ASTM F2229 stainless steel composition e.g., commercially available BioDur® 108 stainless steel
  • ASTM F1586 stainless steel composition e.g., commercially available BioDur® 734 stainless steel
  • HNHC stainless steel high nitrogen, high chromium stainless steel
  • ASTM F2229 stainless steel is an essentially nickel- and cobalt-free nitrogen- strengthened stainless steel with excellent biocompatibility and approved by the Federal Drug Administration for medical use. It is produced by the Electro-Slag Remelting (ESR) process to assure its microstructural integrity and cleanness and is used in applications such as implantable orthopedic devices, high-strength surgical instrumentation, and orthodontic devices. With no intentional additions of cobalt, it complies with the European Union Medical Device Regulation 2017/745 that requires devices containing more than 0.10 wt.% cobalt content to indicate the presence of cobalt as a potential carcinogenic, mutagenic, reproductive toxin substance.
  • ESR Electro-Slag Remelting
  • ASTM F2229 stainless steel also does not contain intentionally added nickel, a metal known to cause cutaneous inflammations and to lead to allergy reactions, teratogenicity and carcinogenicity in medical application (see Yang et al., Nickel-free austenitic stainless steels for medical applications, Set. Technol. Adv. Mater. 11 (2010) 014105).
  • ASTM F2229 stainless steel is limited in view of its relative softness when manufactured by conventional methods, e.g., typically about 300 HV.
  • BioDur® 108 stainless steel manufactured by Carpenter Technology and CHRONIFER® 108 nickel free stainless steel distributed by L. Klein SA (Switzerland) are examples of an alloy compatible with the ASTM F2229 stainless steel standard.
  • ASTM F1586 stainless steel is an essentially cobalt-free nitrogen-strengthened stainless steel approved by the Federal Drug Administration for medical use. It is also compatible with the European Union Medical Device Regulation 2017/745 and used in implantable orthopedic parts such as bone plates, bone screws, and hip and knee components.
  • the ASTM F1586 stainless steel standard calls for 9.00 to 11.00 wt.% Ni. BioDur® 734 manufactured by Carpenter
  • HNHC stainless steel is an essentially cobalt-free nitrogen-strengthened stainless steel manufactured using a powder metallurgy process consisting in atomizing and consolidating powder to form a billet. It is also compatible with the European Union Medical Device Regulation 2017/745 and contains up to 8.00 wt.% Ni. Its composition renders it able to generate high levels of strength through cold working.
  • Stainless steels that may be processed in accordance with embodiments of the invention have compositions selected from the range indicated in the fifth column of Table 1 below. This range encompasses the ranges for the ASTM F2229 stainless steel composition, the ASTM F1586 stainless steel composition, and the HNHC stainless steel composition, which are also given in Table 1. The preferred limits for each element are discussed below. The balance of all three alloys is iron and impurities resulting from normal manufacture.
  • Table 1 Composition of stainless steels in wt.%.
  • Cobalt is an element that is not intentionally added to any of the alloys in Tables 1 and 2. Residual cobalt resulting from normal manufacture is kept below 0.10 wt.% to be compatible with the European Union Medical Device Regulation 2017/745 and preferably below 0.010 wt.%.
  • the major function of manganese in the subject alloys is to increase solubility for nitrogen; the specific level of manganese (within the ranges listed in Tables 1 and 2) is selected to provide the desired nitrogen level. 21.00 wt.% to 24.00 wt.% of Ni is needed in ASTM F2229 stainless steel to allow up to 1.10 wt.% ofN in solution.
  • the ASTM F2229 and ASTM F1586 stainless steels require similar levels of Cr (19.00 wt.% to 23.00 wt.%) to reach the desired corrosion resistance.
  • the HNHC stainless steel requires 27 wt.% to 30 wt.% Cr for extra corrosion resistance and use in harsher environment.
  • Molybdenum significantly improves resistance to corrosion, particularly the types of localized corrosion of concern in implant applications. However, molybdenum also significantly decreases austenitic stability. Like chromium, the levels of molybdenum (within the ranges listed in Tables 1 and 2) are selected to provide the required corrosion resistance and are balanced by the other elements; the levels of other elements are then adjusted as necessary to maintain austenitic stability.
  • a high level of nitrogen increases the strain hardening rate of a stainless steel during cold working, i.e., the strength gained during a cold working deformation step with a given level of cold working increases with the level of nitrogen. Excessive nitrogen levels can result in difficulties in melting, atomizing, consolidating, forging and other process steps.
  • Nitrogen levels (within the ranges listed in Tables 1 and 2) are controlled by controlling the levels of the other elements that affect nitrogen solubility.
  • Silicon additions provide deoxidation during the melting and refining processes; the specific levels used depend upon the melting process employed. Since increasing silicon decreases both austenitic stability and nitrogen solubility, the silicon level is limited to 0.75 wt.% in ASTM F2229 and ASTM F1586 stainless steels, and no more than 1 wt.% (in total with silicon, oxygen, carbon and sulfur) in HNHC stainless steel described in, e.g., U.S. Patent No. 6,168,755.
  • Phosphorus is not intentionally added but is present as an impurity in the raw materials commonly used for melting alloys such as those in Tables 1 and 2. Since excessive levels of phosphorus can decrease certain properties such as ductility, melting and refining procedures are used such that phosphorus level is less than 0.020 wt.% of 0.025 wt.% at most. Like phosphorus, sulfur is not intentionally added, but is present as an impurity in the raw materials commonly used for melting alloys such as those in Tables 1 and 2.
  • sulfur level is less than 0.010 wt.% in ASTM F2229 and ASTM F1586 stainless steels, and no more than 1 wt.% (in total with silicon, oxygen, carbon and sulfur) in HNHC stainless steel described in, e.g., U.S. Patent No. 6,168,755.
  • Carbon in solid solution helps stabilize the austenite phase. Carbon also can combine with various elements to form carbide phases. Since formation of chromium carbides on grain boundaries can result in decreased corrosion resistance, austenitic alloys designed for high corrosion resistance often have low carbon levels. Carbon in the ASTM F2229 and ASTM F1586 stainless steel alloys is restricted to levels less than 0.08 wt.%, and no more than 1 wt.% (in total with silicon, oxygen, carbon and sulfur) in HNHC stainless steel described in, e.g., U.S. Patent No. 6,168,755.
  • the processes described herein employ methods known to those of skill in the art to manufacture the alloys described above, and include multiple additional steps to form an article including a surface layer.
  • the processes include melting of raw material, atomizing or casting the molten metal, conversion from ingot to billet during forging, and a final annealing heat treatment of the billet. This is followed by a cold working step, i.e., a deformation step performed at low temperature to shape the article and increase its bulk yield strength and ultimate tensile strength.
  • a case hardening step of the article is performed at low temperature to improve the properties of the surface of the article. Unlike conventional methods, the case hardening step is not preceded by an annealing step.
  • Ingots made from the ASTM F2229 stainless steel described above may be manufactured by arc melting or vacuum induction melting (VIM) followed by electro-slag remelting (ESR). After solidification, ingots of ASTM F2229 stainless steel are homogenized in a furnace to ensure a homogenous microstructure and converted to billets via hot working on a press or radial forging machine as per the Carpenter Technology BioDur® 108 technical datasheet, which is hereby incorporated by reference in its entirety, for all purposes (Carpenter Technology Corporation, CarTech® BioDur® 108 Alloy).
  • billets of ASTM F2229 stainless steel may be annealed to a temperature ranging from 1900 °F (1038 °C) to 2100 °F (1149 °C) for a duration of one hour and then rapidly cooled to room temperature to prevent the formation of chromium nitrides between 1500 °F (816 °C) and 1800 °F (982 °C).
  • this annealing step is defined as a thermal process performed in air, protective atmosphere or vacuum to relax internal stresses and soften the material through recovery or recrystallization.
  • Ingots made from the ASTM F1586 stainless steel described above may be manufactured by arc melting or vacuum induction melting (VIM) followed by electro-slag remelting (ESR). After homogenization and forging, billets of ASTM F1586 stainless steel may be annealed to a temperature ranging from 1922 °F (1050 °C) to 2102°F (1150°C) and rapidly quenched to prevent the formation of chromium nitrides, as per the Carpenter Technology BioDur® 734 technical datasheet, which is hereby incorporated by reference in its entirety, for all purposes (Carpenter Technology Corporation, CarTech® BioDur® 734 Alloy)
  • the HNHC stainless steel may be manufactured using powder metallurgy (PM) technology to produce powder that is consolidated into fully dense ingots via hot isostatic pressing (HIP). After forging, the billets may be annealed at 2000 °F (1093 °C) for one hour and rapidly quenched to prevent the formation of chromium nitrides, as per the recommendations described under the filing code ASM SS-1231 in the “Alloy Digest - Data on World Wide Metals and Alloys”.
  • PM powder metallurgy
  • HIP hot isostatic pressing
  • Cold working is defined as the forming step consisting of but not limited to a combination of cold rolling, cold drawing, shot peening, and/ or pilgering performed at or below 2/3 of the solidus temperature.
  • the solidus temperature (defined as the highest temperature below which the alloy is fully solid) is at least 2400 °F (1316 °C) and 2/3 of this temperature is about 1600 °F (871 °C).
  • a cold forming step is understood as a forming step performed between room temperature and 1600 °F (871 °C).
  • Cold working performed in the 1000 °F (538 °C) to 1600 °F (871 °C) temperature range may sometimes be referred to as “warm working”. Accordingly, as used herein, “cold working” encompasses cold and warm working, i.e., a forming step performed between room temperature and 1600 °F (871 °C).
  • Warm working (cold working) performed in the 1000 °F (538 °C) to 1600 °F (871 °C) temperature range may be a preferred processing step as a deformation performed in that temperature range is easier, i.e., requires less external strength applied to the article to reach the desired level of deformation.
  • Deformation performed in the 1000 °F (538 °C) to 1600 °F (871 °C) temperature range introduces less defects (for example dislocations, point defects) in the article and creates less energy stored in the article. Articles with less stored energy available for recovery or recrystallization are more likely to maintain their required bulk strength during further process, such as a case hardening step.
  • the alloys are preferably cold worked (i.e., deformed at a low temperature below 1600 °F/871 °C) to make them stronger.
  • ASTM F2229 stainless steel, ASTM F1586 stainless steel and HNHC stainless steel have different compositions and different work hardenability, i.e., they harden differently when subjected to the same cold forming step and require different levels of cold working to reach the same level of mechanical properties.
  • Figure 1 is adapted from MJ Walter, Stainless steel for medical implants:
  • the high level of nitrogen in BioDur® 108 stainless steel provides enhanced mechanical and physical properties for medical implants, Adv. Mater. Process. 164 (2006) 84-86, and also adapted from the Carpenter Technology BIODUR® 108 STAINLESS data sheet, which are hereby incorporated by reference in their entireties, for all purposes.
  • YS yield strength
  • UTS ultimate tensile strength
  • a suitable cold working process of 15 % is preferred for a part made of that alloy to reach the ASTM 799 standard mechanical properties (120 ksi YS / 170 ksi UTS at room temperature), which is hereby incorporated by reference in its entirety, for all purposes.
  • ASTM 799 standard mechanical properties 120 ksi YS / 170 ksi UTS at room temperature
  • Figure 2 is adapted from the Carpenter Technology BIODUR® 734 STAINUESS datasheet, which is hereby incorporated by reference in its entirety, for all purposes.
  • ASTM F1586 stainless steel in the annealed condition offers 65 ksi YS / 122 ksi UTS at room temperature and 128 ksi YS / 170 ksi UTS after 35 % of cold working.
  • a suitable cold working process of at least 40 % is preferred for a part made of that alloy to reach the ASTM 799 standard mechanical properties (120 ksi YS / 170 ksi UTS at room temperature).
  • ASTM 799 standard mechanical properties 120 ksi YS / 170 ksi UTS at room temperature.
  • a different level of cold working may be desired to target a specific combination of YS and UTS.
  • Figure 3 is adapted from the Carpenter Technology CarTech® Micro-Melt® NCORRTM Stainless Steel datasheet, which is hereby incorporated by reference in its entirety, for all purposes.
  • the HNHC stainless steel in the annealed condition offers 100 ksi YS / 153 ksi UTS at room temperature and 264 ksi YS / 328 ksi UTS after 70 % of cold working.
  • a suitable cold working process of at least 15 % is preferred for a part made of that alloy to reach the ASTM 799 standard mechanical properties (120 ksi YS / 170 ksi UTS at room temperature).
  • a different level of cold working may be desired to target a specific combination ofYS and UTS.
  • Case hardening is a surface modification process used to harden the surface layer of stainless steels. Accordingly, a case-hardening step may be used to increase the hardness of the surface of ASTM F2229 stainless steel, ASTM F1586 stainless steel, or HNHC stainless steel such as ASM SS-1231 stainless steel via diffusion of interstitial elements such as carbon, nitrogen, boron or a combination thereof in, for example, a gas, ion or plasma media or in vacuum. In the case of pack carburizing, pack nitriding or pack boriding, the case hardening step may be conducted in a material that is enriched in carbon, nitrogen, or boron.
  • This step may include carburizing, nitriding, boriding, carbonitriding or a combination thereof at a case hardening temperature below 1000 °C to prevent the formation of deleterious second phases.
  • This process results in the formation of a surface layer that is much harder than the bulk of the material and also has improved resistance to wear, corrosion, and fatigue damage.
  • Case hardening can be used to improve the surface properties of ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel and improve the corrosion, fatigue and wear resistance of these alloys, resulting in better performances in various applications, such as articulating orthopedic applications.
  • case hardening is a heat treatment process in a C-rich, N-rich, B-rich, or a combination thereof or other suitable environment used to alter the near surface chemistry of the alloy through a diffusion process to alter the properties. It allows interstitial elements to diffuse into the surface layer of the material.
  • the case-hardening process can be boriding (diffusion of boron), carburizing (diffusion of carbon), nitriding (diffusion of nitrogen), carbonitriding (simultaneous diffusion of carbon and nitrogen) or a combination thereof.
  • the case hardening process can be performed using gas, ion or plasma media or in vacuum.
  • interstitial elements diffuse into the surface layer form a supersaturated solid solution at the surface of the material.
  • the process is performed at a temperature sufficiently low to prevent the formation of precipitates and detrimental second phases such as borides, carbides, nitrides or carbonitrides. See XY Li, N Habibi, T Bell, H Dong, “Microstructural characterisation of a plasma carburised low carbon Co-Cr alloy”, Surf. Eng. 23 (2007) 45-51.
  • Case hardening temperatures range between 350 °C and 1000 °C, e.g., 400°C to 1000 °C, and durations can be as long as 60 hours and as short as 1 hour.
  • case hardening temperatures range between 400 °C and 1000 °C, such as 500 °C, 550 °C, 750 °C, or 960 °C.
  • case hardening periods range from 1 hour to 16 hours, such as 1 hour, 4 hours, 5 hours or 16 hours.
  • the temperature at which the alloy is case hardened increases the diffusivity of carbon, nitrogen and boron, i.e., the higher the case hardening temperature, the easier it is to introduce a larger amount of interstitial elements in the case layer and the thicker the caser layer.
  • a case hardening step performed at a higher temperature is more efficient, i.e.
  • case hardening temperature and time must be balanced and adapted to the alloy composition to create the desired case layer thickness and avoid the formation of detrimental carbide and nitride.
  • a minimum case surface layer thickness of 10 pm is desired to allow parts to be machined, 100 pm is a more preferred thickness and 1,000 pm is an even more preferred thickness.
  • a surface hardness of at least 400 HV is desired for applications that require wear resistance, preferably 800 HV, more preferably 900 HV and even more preferably 1200 HV.
  • the combination of surface hardness and case layer thickness is determined by the final application, as some applications need a shallower but harder surface layer and others need a thicker but softer case surface layer.
  • the case hardening is performed at a single case hardening temperature to simplify the process and minimize the risk of forming deleterious phases during the heat up and cool down ramps.
  • Samples may be subjected to other temperatures during the case hardening process, for example during the heating part of the cycle, from room temperature to the case hardening temperature, e.g., a carburizing temperature, and during the cooling part of the cycle, from the case hardening temperature to room temperature.
  • the case hardening cycle may be interrupted (i.e., introduction of boron, carbon, and/or nitrogen temporarily stopped) to allow interstitial elements to diffuse into the surface layer of the material, while maintaining the material at the case hardening temperature.
  • the case hardening cycle may also include a succession of short case hardening pulses at the case hardening temperature and diffusion periods to allow interstitial elements to diffuse into the surface layer of the material.
  • case hardening process results in the formation of a surface layer that is much harder than the bulk of the material (see schematic example in Figure 4) and has improved resistance to wear, corrosion, and fatigue damage.
  • cold- worked (including warm-worked) articles of ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel are subjected to case-hardening heat treatments.
  • case hardening heat treatment cycles are offered by various commercial vendors: Kolsterising® (proprietary to Bodycote), ExpaniteHigh-T, ExpaniteLow-T and SuperExpanite (proprietary to Expanite A/S) or Infracarb® (proprietary to ECM-USA).
  • Kolsterising® proprietary to Bodycote
  • ExpaniteHigh-T ExpaniteHigh-T
  • ExpaniteLow-T SuperExpanite
  • Infracarb® proprietary to ECM-USA
  • commercial nitriding, carbonitriding or boriding case hardening heat treatment cycles are available from the same vendors.
  • An exemplary system for performing a case hardening step (carburizing step called pack carburizing) on stainless steels described herein is a high-temperature furnace, e.g., the RD7- KHE24 box furnace manufactured by Lucifer Furnaces Inc.
  • a mixture of pelletized carbon and sodium carbonate anhydrous may be placed in a metallic container.
  • a suitable composition may be 98 % (in weight) of pelletized carbon and 2 % (in weight) of sodium carbonate anhydrous.
  • the metallic container may be a stainless steel rectangular box topped with a stainless steel lid and sealed with a high-temperature refractory cement. The metallic container with the mixture may then be placed into the furnace along with the article to be case hardened.
  • the mixture and article are heated to the desired case hardening temperature for a sufficient period of time to obtain a surface layer on a top surface of the article with the desired concentration of interstitial elements, and are then rapidly cooled to room temperature via quenching in water, oil, air, or any other fluid.
  • interstitial elements in solution After case hardening, interstitial elements in solution generate compressive stresses that make the surface layer much harder and more resistant to fatigue and wear than the bulk of the material. The higher concentration of interstitial elements in the surface layer makes it more resistant to corrosion damage.
  • ASTM F2229 stainless steel contains at most 0.08 wt.% of carbon. After carburizing, the concentration of carbon in the surface layer is at least 0.10 wt.% and preferably at most 5.00 wt.% o
  • Nitriding the typical nitrogen level in the ASTM F2229 stainless steel ranges between 0.85 wt.% and 1.10 wt.%. After nitriding, the nitrogen concentration in the surface layer ranges from at least 1. 10 wt.% at a top surface thereof to a range of 0.85 wt.% to 1.10 wt.% N in the bulk material, with the nitrogen concentration in the surface layer being higher than in the bulk material.
  • Boriding the nominal composition of the ASTM F2229 stainless steel does not include boron. A boriding case-hardening heat treatment results in a surface layer that contains at least 0.05 wt.% B. o Combinations thereof.
  • ASTM F1586 stainless steel contains at most 0.08 wt.% of carbon. After carburizing, the concentration of carbon in the surface layer is at least 0.10 wt.% and preferably at most 5.00 wt.% o
  • Nitriding the typical nitrogen level in the ASTM F1586 stainless steel ranges between 0.25 wt.% and 0.50 wt.%. After nitriding, the nitrogen concentration in the surface layer ranges from at least 0.50 wt.% at a top surface thereof to a range of 0.25 wt.% and 0.50 wt.% N in the bulk material, with the nitrogen concentration in the surface layer being higher than in the bulk material.
  • Boriding the nominal composition of the ASTM F1586 stainless steel does not include boron. A boriding case-hardening heat treatment results in a surface layer that contains at least 0.05 wt.% B. o Combinations thereof.
  • HNHC stainless steel o Carburizing the HNHC stainless steel contains at most 0.03 wt.% of carbon.
  • the concentration of carbon in the surface layer is at least 0.10 wt.% and preferably at most 5.00 wt.% o
  • Nitriding the typical nitrogen level in the HNHC stainless steel between 0.80 wt.% and 0.90 wt.%. After nitriding, the nitrogen concentration in the surface layer ranges from at least 0.90 wt.% at a top surface thereof to a range of 0.80 wt.% to 0.80 wt.% N in the bulk material, with the nitrogen concentration in the surface layer being higher than in the bulk material.
  • o Boriding the nominal composition of the HNHC stainless steelf does not include boron. A boriding case-hardening heat treatment results in a surface layer that contains at least 0.05 wt.% B. o Combinations thereof.
  • a hip prosthesis 500 may include an acetabular socket 510, an insert 520, a femoral head 530, a femoral trunnion 540, and a femoral stem 550.
  • the insert 520 e.g., polyethylene insert made of ultra-high-molecular-weight polyethylene or UHMWPE
  • UHMWPE ultra-high-molecular-weight polyethylene
  • the femoral trunnion 540 i.e., a tapered portion of the hip prosthesis 500, is disposed between the femoral head 530 and the femoral stem 550. As illustrated, the femoral stem 550 may be implanted in a femur 560 of a patient.
  • a hip joint prosthesis typically has at least three elements: femoral stem 550 including a stem portion and a neck (trunnion 540) made of metal, a femoral head 530 made of metal or ceramic, and an acetabular socket 510 that can be made of metal, ceramic or polymer (e.g., polyethylene); these three elements may be fabricated from stainless steel in accordance with embodiments of the invention.
  • femoral stem 550 including a stem portion and a neck (trunnion 540) made of metal, a femoral head 530 made of metal or ceramic, and an acetabular socket 510 that can be made of metal, ceramic or polymer (e.g., polyethylene); these three elements may be fabricated from stainless steel in accordance with embodiments of the invention.
  • hip prosthesis elements that may fabricated in accordance with embodiments of the invention include a femoral stem, a femoral head, and an acetabular socket.
  • An element formed by processes described herein has the required mechanical properties to be used in the articulating part of the joint replacement.
  • required mechanical properties include a bulk strength of 120 ksi YS and 170 ksi UTS at room temperature to make the article compatible with the ASTM 799 requirement and a hardness of at least 350 HV.
  • an articulating orthopedic device may include a first element consisting essentially of cold worked ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel and having a first articular surface; and a second element consisting essentially of cold worked ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel and having a second articular surface configured to articulate with the first articular surface.
  • the first and second articular surfaces each include a surface layer consisting of hardened ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel with at least one of carbon, nitrogen, or boron diffused therein.
  • the first element may be an acetabular socket and the second element may be a femoral head. In other embodiments, the first element may be a femoral head and the second element may be a femoral stem.
  • flat discs made of ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel can be cold formed to produce acetabular shell blanks and further processed according to embodiments of the invention.
  • Spinal rods can also be made from ASTM F2229 stainless steel, ASTM F1586 stainless steel orthe HNHC stainless steel using the processes described herein.
  • a damaged bone and cartilage may be removed and replaced with at least some prosthetic components.
  • a damaged femoral head may be removed and replaced with femoral head 530 attached to a femoral stem 550 that can be placed into the hollow center of the femur 560 by either cementing or press fitting the femoral stem 550 into the femur 560.
  • a damaged femoral head may be removed and replaced by placing the femoral head 530 on the upper part of the femoral stem.
  • the femoral head 530 includes a structure (e.g., ball structure) that connects to the femoral stem 550 via the femoral trunnion 540.
  • a damaged cartilage surface of a socket acetabulum
  • screws or cement are used to hold the socket in place.
  • the insert 520 e.g., a plastic, ceramic, or metal spacer
  • Materials and methods described herein may be used to fabricate watch structural elements such as cases, rings, gears, bracelets, or sections thereof and pins to hold the bracelets.
  • materials and methods described herein may be used to fabricate non-magnetic parts for applications in the electrification and electronics markets that require high resistance to wear and corrosion such as retainer rings.
  • materials and methods described herein may be used to fabricate instrumentation/non-magnetic housings for the oil & gas industry, as well as bearings, gears, gear teeth, and pump shafts.
  • composition example in Table 1 describes articles made of ASTM F2229 stainless steel, ASTM F1586 stainless steel or HNHC stainless steel after a cold deformation and case hardening step. Further, exemplary compositions in weight percent are given in Table 3 below.
  • Table 3 Composition in wt.% of the experimental stainless-steel alloys melted at Carpenter Technology.
  • Condition B cold working (deformation at room temperature) + low pressure carburizing 4 hr at 550 °C
  • Condition C cold working (warm) (deformation at 1200 °F) + low pressure carburizing 4 hr at 550 °C
  • Condition D cold working (deformation at room temperature) + low pressure carburizing 16 hr at 550 °C
  • Condition E cold working (warm) (deformation at 1200 °F) + low pressure carburizing 16 hr at 550 °C
  • Condition F cold working (deformation at room temperature) + low pressure carburizing 4 hr at 750 °C
  • Condition G cold working (warm) (deformation at 1200 °F) + low pressure carburizing 4 hr at 750 °C
  • Condition H cold working (deformation at room temperature) + low pressure carburizing 5 hr at 960 °C
  • Figure 6A is a graph illustrating the microhardness (hardness according to Vickers (HV)) of the surface layer of samples of BioDur® 108 stainless steel after five different processing conditions: conditions D, E, F, G, and H. As shown in Figure 6A, the bulk hardness is about 400 HV and the peak hardness at the surface ranges between at least 510 HV and at least 850 HV depending on the processing conditions.
  • Figure 6B shows the amount of carbon in solution in the surface layer of samples of BioDur® 108 stainless steel after four different processing conditions: conditions A, B, G and H. The carbon level is close to 0.10 wt.% in the bulk and ranges from 0.50 wt.% to 3.65 wt.% in the surface layer depending on the processing conditions.
  • Figure 6C includes light optical micrographs showing the visible case layer of some conditions as shown in Figure 6A.
  • the light optical micrographs in Figure 6C were taken after etching with waterless Kalling's etchant (conventional mixture of acids used to reveal the alloy microstructure) and show the case surface layer (in brighter tone) and the bulk (darker tone).
  • the thickness of the visible case surface layer is about 20-25 pm (condition A and condition B), 40-50 pm (condition D), 70-80 pm (condition F) or 200-300 pm (condition H).
  • Figure 7A is a graph illustrating the microhardness (HV) of the surface layer of samples of BioDur® 734 stainless steel processed according to four processing conditions: conditions D, E, F, and G.
  • the bulk hardness is about 350 HV to 400 HV.
  • the hardness of the case layer ranges between 500 HV and 900 HV depending on the processing conditions.
  • Figure 7B is a graph illustration the carbon composition of the surface layer of samples of BioDur® 734 stainless steel processed according to two processing conditions: conditions D and G.
  • the carbon composition peak in the surface layer ranges between 0.90 wt.% and 3.20 wt.%.
  • Figure 7C includes light optical micrographs showing the visible case surface layer formed after case hardening in accordance with conditions as shown in Figure 7A and Figure 7B. As shown in Figure 7C, the case surface layer thickness is 30 to 40 pm (condition D and condition E) or 50 pm to 60 pm (condition F and condition G).
  • Figure 8A is a graph illustrating the microhardness (HV) of the surface layer of samples of NCORRTM stainless steel alloy processed according to two conditions: condition F (cold-worked (deformation at room temperature) + carburizing 4 hr at 750 °C) and condition G (cold-worked (warm-worked) (deformation at 1200 °F) + carburizing 4 hr at 750 °C).
  • condition F cold-worked (deformation at room temperature) + carburizing 4 hr at 750 °C
  • condition G cold-worked (warm-worked) (deformation at 1200 °F) + carburizing 4 hr at 750 °C).
  • the bulk hardness is about 350-400 HV and the peak hardness at the surface reached 850 HV to 900 HV.
  • Figure 8B is a graph illustration the carbon composition of the surface layer of samples of NCORRTM stainless steel processed according to two processing conditions: conditions F and G.
  • Figure 8C includes light optical micrographs showing the visible case surface layer of each condition illustrated in Figure 8A and Figure 8B. As shown in Figure 8C, the case surface layer thickness is about 50 pm to 70 pm (for both conditions).

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