Method of making ultra-high strength stainless steels

Patent metadata

Field	Value
Publication number	US-9562274-B2
Application number	US-201113226514-A
Country	US
Kind code	B2
Filing date	Sep 7, 2011
Priority date	Jun 19, 2007
Publication date	Feb 7, 2017
Grant date	Feb 7, 2017

Abstract

An ultra-high strength stainless steel alloy with enhanced toughness includes in % by weight: 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities. The heat treating method includes the steps of austenitizing at least once followed by quenching, tempering and sub-zero cooling to obtain no more than about 6-8% retained austenite in the finished alloy.

First claim

What is claimed is:

1. A method of making an ultra-high strength stainless steel alloy suitable in the manufacture of aircraft landing gear comprising the steps of:
(a) providing an alloy comprising 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 18.0 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities;
(b) austenitizing the alloy;
(c) cooling the austenitized alloy to room temperature; and
(d) tempering the austenitized and cooled alloy,
wherein step (d) is performed after step (c) without any further processing being conducted in between.

2. A method of making an ultra-high strength stainless steel alloy suitable in the manufacture of aircraft landing gear comprising the steps of:
(a) providing an alloy comprising 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities;
(b) austenitizing the alloy a first time;
(c) cooling the alloy austenitized for the first time to room temperature;
(d) austenitizing the alloy a second time;
(e) cooling the alloy austenitized for the second time to room temperature;
(f) tempering the alloy; and
(g) cooling the alloy to a temperature of about −100° C. to reduce retained austenite to no more than about 6 to 8 vol.%.

3. The method of claim 1 , wherein in step (b), the alloy is austenitized at a temperature of 900-1050° C.

4. The method of claim 1 , wherein in step (d), the alloy is tempered at a temperature of 475-575° C.

5. The method of claim 2 , wherein in steps (b) and (d), the alloy is austenitized at a temperature of 900-1050° C.

6. The method of claim 2 , wherein in step (f), the alloy is tempered at a temperature of 475-575° C.

7. A method of making an ultra-high strength stainless steel alloy suitable in the manufacture of aircraft landing gear comprising the steps of:
(a) providing an alloy comprising 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities;
(b) austenitizing the alloy a first time;
(c) cooling the alloy austenitized for the first time to room temperature;
(d) austenitizing the alloy a second time;
(e) cooling the alloy austenitized for the second time to room temperature;
(f) tempering the alloy; and
(g) cooling the alloy to a sub-zero temperature to reduce retained austenite to no more than about 6 to 8 vol.%.

8. The method of claim 7 , wherein in step (b), the alloy is austenitized at a temperature of 900-1050° C.

9. The method of claim 7 , wherein in step (d), the alloy is tempered at a temperature of 475-575° C.

10. A method of making an ultra-high strength stainless steel alloy suitable in the manufacture of aircraft landing gear comprising the steps of:
(a) providing an alloy comprising 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 6 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities;
(b) austenitizing the alloy;
(c) cooling the austenitized alloy to room temperature; and
(d) tempering the austenitized and cooled alloy,
wherein step (d) is performed after step (c) without any further processing being conducted in between.

11. The method of claim 10 , wherein in step (b), the alloy is austenitized at a temperature of 900-1050° C.

12. The method of claim 10 , wherein in step (d), the alloy is tempered at a temperature of 475-575° C.

13. The method of claim 10 , wherein after step (d), the alloy has a yield strength of 1600-1800 MPa and a microstructure of martensite and austenite.

14. A method of making an ultra-high strength stainless steel alloy suitable in the manufacture of aircraft landing gear comprising the steps of:
(a) providing an alloy comprising 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); balance iron (Fe) and incidental deoxidizers and impurities, wherein Mo is >0 atomic % and <6 atomic %, W is >0 atomic % and <6 atomic %, and Mo+W is 1.5-6.0 atomic %;
(b) austenitizing the alloy;
(c) cooling the austenitized alloy to room temperature; and
(d) tempering the austenitized and cooled alloy,
wherein step (d) is performed after step (c) without any further processing being conducted in between.

15. The method of claim 14 , wherein in step (b), the alloy is austenitized at a temperature of 900-1050° C.

16. The method of claim 14 , wherein in step (d), the alloy is tempered at a temperature of 475-575° C.

17. The method of claim 14 , wherein after step (d), the alloy has a yield strength of 1600-1800 MPa and a microstructure of martensite and austenite.

18. The method of claim 1 , wherein after step (d), the alloy has a yield strength of 1600-1800 MPa and a microstructure of martensite and austenite.

Assignees

• Garrison Jr Warren M
• Univ Carnegie Mellon

Inventors

• Garrison Jr Warren M

Classifications

• C21D9/32

  for gear wheels, worm wheels, or the like · CPC title

• C21D2211/004

  Dispersions; Precipitations · CPC title

• C21D6/04

  Hardening by cooling below 0 degrees Celsius · CPC title

• C21D6/004 Primary

  containing Cr and Ni · CPC title

• C21D6/007

  containing Co · CPC title