High toughness secondary hardening steels with nickel as a primary strength and toughening agent

Patent metadata

Field	Value
Publication number	US-10428410-B2
Application number	US-201615136205-A
Country	US
Kind code	B2
Filing date	Apr 22, 2016
Priority date	Oct 29, 2010
Publication date	Oct 1, 2019
Grant date	Oct 1, 2019

Abstract

Steel alloys having high yield and ultimate tensile strengths in combination with high toughness based on medium carbon secondary hardening steel compositions having low cobalt content. Nickel is added to the medium carbon secondary hardening steel compositions to increase the yield and tensile strengths and fracture toughness. Applications of a steel alloy of the present disclosure include structural applications requiring high strength and high fracture toughness, such as aircraft landing gear.

First claim

What is claimed is:

1. A steel alloy, comprising:
a medium carbon secondary hardening steel composition containing:
0.3-0.45 wt. % carbon;
4-6 wt. % chromium;
0-2.5 wt. % molybdenum;
0-3 wt. % tungsten;
0-1.0 wt. % vanadium;
less than 0.75 wt. % silicon;
less than 3 wt. % cobalt; and
less than 1 wt. % manganese; and

an addition of nickel to the medium carbon secondary hardening steel composition in a range of about 3 wt. % to about 7 wt. % that:
provides a V-notch Charpy energy of at least 20.7 joules;
increases a yield strength of the medium carbon secondary hardening steel composition to at least 1500 MPa;
increases an ultimate tensile strength of the medium carbon secondary hardening steel composition to at least 1800 MPa; and
increases a K Ic fracture toughness of the medium carbon secondary hardening steel to at least about 86 MPa√m.

2. The steel alloy according to claim 1 , wherein the addition of nickel is in a range of about 4 wt. % to about 6 wt. %.

3. The steel alloy according to claim 1 , wherein the addition of nickel is in a range of about 3 wt. % to about 4 wt. %.

4. The steel alloy according to claim 1 , wherein the addition of nickel is in a range of about 5 wt. % to about 3.5 wt. %.

5. The steel alloy according to claim 1 , wherein the yield strength is at least 1700 MPa and the ultimate tensile strength is at least 1900 MPa.

6. The steel alloy according to claim 1 , wherein the K Ic fracture toughness is at least 100 MPa√m.

7. The steel alloy according to claim 1 , wherein the wt. % cobalt is less than about 0.05%.

8. The steel alloy according to claim 1 , wherein the medium carbon secondary hardening steel contains:
about 0.38 wt. % carbon;
about 4.5 wt. % chromium;
about 2.0 wt. % molybdenum;
about 0.0 wt. % tungsten;
about 0.5 wt. % manganese and
about 0.5 wt. % vanadium.

9. The steel alloy according to claim 8 , wherein the addition of nickel is in a range of 0.5 wt. % to 4 wt. %.

10. The steel alloy according to claim 8 , wherein the addition of nickel is in a range of 0.5 wt. % to 3.5 wt. %.

11. The steel alloy according to claim 1 , wherein the medium carbon secondary hardening steel contains:
about 0.40 wt. % carbon;
about 5.0 wt. % chromium;
about 1.3 wt. % molybdenum;
about 0.5 wt. % tungsten; and
about 0.5 wt. % vanadium.

12. The steel alloy according to claim 11 , wherein the addition of nickel is in a range of about 3 wt. % to 4 wt. %.

13. The steel alloy according to claim 11 , wherein the addition of nickel is in a range of 3 wt. % to 3.5 wt. %.

14. A method of making the steel alloy of claim 1 , comprising:
vacuum induction melting the medium carbon secondary hardening steel composition with the addition of the nickel;
vacuum arc remelting the medium carbon secondary hardening steel composition with the addition of the nickel;
following vacuum arc remelting, quenching the steel alloy to at least facilitate a phase transformation from austenite;
refrigerating the steel alloy to reduce the amount of retained austenite; and
tempering the steel alloy to reduce the amount of retained austenite.

Assignees

• Univ Carnegie Mellon

Inventors

• Garrison Jr Warren M

Classifications

• C21D2211/001

  Austenite · CPC title

• C21D1/18

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• C22C38/46 Primary

  with vanadium · CPC title

• C22C38/44

  with molybdenum or tungsten · CPC title

• C22C38/42

  with copper · CPC title