Nanocarbide precipitation strengthened ultrahigh-strength, corrosion resistant, structural steels

• US 7,160,399 B2
• Filed: 02/06/2003
• Issued: 01/09/2007
• Est. Priority Date: 02/09/2001
• Status: Expired due to Term

• Current Assignee: Questek Innovations Llc
• Original Assignee: Questek Innovations Llc
• Inventors: Kuehmann, Charles J., Jou, Herng-Jeng, Olson, Gregory B.
• Primary Examiner(s): WYSZOMIERSKI, GEORGE P
• Application Number:
  US10/360,204
• Publication Number:
  US 20030226625A1
• Time in Patent Office: 1,433 Days
• Field of Search: 148/335, 148/334, 148/333, 148/328, 148/326, 148/325, 420/36, 420/107, 420/37
• US Class Current: 148/326
• CPC Class Codes: B22F 2998/00 Supplementary information concerning processes or compositions relating to powder metallurgy
• CPC Class Codes: C21D 2211/003 Cementite
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 6/02 Hardening by precipitation
• CPC Class Codes: C21D 6/04 Hardening by cooling below 0 degrees Celsius
• CPC Class Codes: C21D 8/005 of ferrous alloys C21D8/02 - C21D8/12 take precedence
• CPC Class Codes: C22C 33/0285 with Cr, Co, or Ni having a minimum content higher than 5%
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 with vanadium
• CPC Class Codes: C22C 38/50 with titanium or zirconium
• CPC Class Codes: C22C 38/52 with cobalt

Abstract

A nanocarbide precipitation strengthened ultrahigh-strength, corrosion resistant, structural steel possesses a combination of strength and corrosion resistance comprising in combination, by weight, about: 0.1 to 0.3% carbon (C), 8 to 17% cobalt (Co), 0 to 10% nickel (Ni), 6 to 12% chromium (Cr), less than 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15% copper (Cu), with additives selected from the group comprising about: less than 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium (V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinations thereof, with additional additives selected from the group comprising about: less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rare earth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B), and combinations thereof, impurities of less than about: 0.02% sulfur (S), 0.012% phosphorus (P), 0.015% oxygen (O) and 0.015% nitrogen (N), the remainder substantially iron (Fe), incidental elements and other impurities. The alloy is strengthened by nanometer scale M₂C carbides within a fine lath martensite matrix from which enhanced chemical partitioning of Cr to the surface provides a stable oxide passivating film for corrosion resistance. The alloy, with a UTS in excess of 280 ksi, is useful for applications such as aircraft landing gear, machinery and tools used in hostile environments, and other applications wherein ultrahigh-strength, corrosion resistant, structural steel alloys are desired.

Claims

1. A structural, stainless steel alloy comprising, in combination, by weight:

about 0.15 to 0.30% carbon (C), about 8 to 17% cobalt (Co), about 2.0 to 10.0% nickel (Ni), about 8.0 to 11.0% chromium (Cr), aboul 1.0 to 3.0% molybdenum (Mo), less than about 0.8% vanadium (V), and less than about 3% tungsten (W), the balance essentially iron (Fe) and incidental elements and impurities, characterized in that the alloy has a predominantly lath martensite microstructure essentially without topologically close packed intermetallic phases and said carbon (C) is in predominantly a dispersion of nanoscale, M₂C carbide particles having a nominal dimension less than about 10 nanometers in diameter, where M is two or more elements selected from the group consisting of Cr, Mo, W, V, Nb and Ta.

2. The alloy of claim 1 wherein M comprises Cr and Mo.

3. The alloy of claim 1 wherein M comprises Cr, Mo and V.

4. The alloy of claim 1 wherein M comprises Mo and one or more elements selected from the group consisting of Cr, W, V, Nb and Ta.

5. The alloy of claim 1 wherein the alloy is processed to an ultimate tensile strength greater than about 260 ksi.

6. The alloy of claim 1 processed to a toughness to strength ratio (K_IC/YS) equal to or greater than about 0.21 √

{square root over (in)} where K_IC is the plane strain fracture toughness and YS is the yield strength.

7. The alloy of claim 1 processed to a tensile strength greater than about 260 ksi and a toughness to strength ratio (K_IC/YS) equal to or greater than about 0.21 √

{square root over (in)} where K_IC is the plane strain fracture toughness and YS is yield strength.

8. The alloy of claim 1 wherein cementite dissolution is effectively complete.

9. The alloy of claim 1 wherein at least one of said elements selected from the group consisting of Mo, W and V is included to effect the formation of M₂C carbide particles.

10. The alloy of claim 9 wherein cementite dissolution is effectively complete.

11. A structural, stainless steel alloy comprising in combination by weight:

about 0.15 to 0.3% carbon (C);

about 8 to 17% cobalt (Co);

about 2.0 to 10% nickel (Ni);

about 8 to 11% chromium (Cr);

molybdenum (Mo);

tungsten (W) and vanadium (V), the molybdenum (Mo) being present in an amount by weight greater than about 1.0 and less than about 3%, the tungsten (W) being present in an amount by weight less than about 3% and the vanadium (V) being present in an amount by weight less than about 0.8%;

the balance essentially iron (Fe) and incidental elements and impurities characterized in that the steel alloy comprises a corrosion resistant, lath martensitic microstructure essentially without topologically close packed intermetallic phases and said carbon (C) is predominantly in a dispersion of nanoscale, M₂C carbide particles having a diameter of 10 nm or less where M comprises Mo and one or more elements selected from the group consisting of Cr, W and V and wherein cementite dissolution is effectively complete.

12. The alloy of claim 11 processed to an ultimate tensile strength greater than about 260 ksi.

13. The alloy of claim 11 processed to a toughness to strength ratio (K_IC/YS) equal to or greater than about 0.21 √

{square root over (in)} where K_IC is the plane strain fracture toughness and YS is the yield strength.

14. The alloy of claim 11 processed to a tensile strength greater than about 260 ksi and a toughness to strength ratio (K_IC/YS) equal to or greater than about 0.21 √

{square root over (in)} where K_IC is the plane strain fracture toughness awn YS is yield strength.

15. The alloy of claim 11 wherein M comprises Cr, Mo and V.

16. The alloy of claim 11 wherein at least one of said elements selected from the group consisting of Mo, W and V is included to effect the formation of M₂C carbide particles.

17. A stainless, structural steel alloy comprising, in combination, by weight:

about 0.15 to 0.30% carbon (C), about 8 to 17% cobal. (Co), about 2.0 to less than 10.0% nickel (Ni), about 8.0 to 11.0% chromium (Cr), about 1.0 to 3.0% molybdenum (Mo), less than about 0.8% vanadium (V), and less than about 3% tungsten (W), the balance essentially iron (Fe) and incidental elements and impurities, characterized in that the alloy his a predominantly lath martensite microstructure essentially without topologically close packed intermetallic phases and said carbon (C) is predominantly in a dispersion of nanoscale, M₂C carbide particles having a nominal dimension less than about 10 nanometers in diameter, where M is two or more elements selected from the group consisting of Cr, Mo, W and V.

18. The alloy of claim 17 wherein M comprises Cr, Mo and V.

19. The alloy of claim 17 processed to an ultimate tensile strength greater than about 260 ksi.

20. The alloy of claim 17 processed to a toughness to strength ratio (K_IC/YS) equal to or greater than about 0.21 √

{square root over (in)} where K_IC is the plane strain fracture toughness and YS is the yield strength.

21. The alloy of claim 17 processed to a tensile strength greater than about 260 ksi and a toughness to strength ratio (K_IC/YS) equal to or greater than about 0.21 √

{square root over (in)} where K_IC is the plane strain fracture toughness and YS is yield strength.

22. The alloy of claim 17 wherein cementite dissolution is effectively complete.

23. The alloy of claim 22 wherein M₂C accounts for about at least 85% by atomic fraction of the carbon (C) content.

24. The alloy of claim 17 wherein at least one of said elements selected from the group consisting of Mo, W and V is included to effect the formation of M₂C carbide particles.