Low alloy high performance steel

Patent metadata

Field	Value
Publication number	US-2016369362-A1
Application number	US-201615160221-A
Country	US
Kind code	A1
Filing date	May 20, 2016
Priority date	Jun 10, 2015
Publication date	Dec 22, 2016
Grant date	—

Abstract

A low alloy, high performance steel having high impact toughness and high ductility, as well as methods of making and heat treating the alloy, are provided. The alloy steel composition consists essentially of about 0.24% to about 0.32% carbon, about 2.00% to about 3.00% chromium, about 0.50% to about 1.50% molybdenum, about 0.05% to about 0.35% vanadium, about 1.00% manganese or less, about 3.00% nickel or less, about 1.50% silicon or less, with minimal impurities, and balance consisting essentially of iron, wherein % is weight percent based on the entire weight of the alloy steel composition. The impurities may include about 0.20% copper or less, about 0.015% phosphorous or less, about 0.012% sulfur or less, about 0.02% calcium or less, about 0.15% nitrogen or less, and/or about 0.025% aluminum or less. Also disclosed is a hardened and tempered article that has high impact toughness, as well as other favorable physical properties.

First claim

What is claimed is:

1 . An alloy steel composition consisting essentially of:
about 0.24% to about 0.32% carbon, about 2.00% to about 3.00% chromium, about 0.50% to about 1.50% molybdenum, about 0.05% to about 0.35% vanadium, about 1.00% manganese or less, about 3.00% nickel or less, about 1.50% silicon or less, about 0.20% copper or less, about 0.015% phosphorous or less, about 0.012% sulfur or less, about 0.02% calcium or less, about 0.15% nitrogen or less, about 0.025% aluminum or less, and balance consisting essentially of iron, wherein % is weight percent based on the entire weight of the alloy steel composition.

2 . The alloy steel composition of claim 1 , consisting essentially of:
about 0.26% to about 0.30% carbon, about 2.20% to about 2.80% chromium, about 0.75% to about 1.25% molybdenum, about 0.05% to about 0.25% vanadium, about 0.10% to about 0.90% manganese, about 0.50% to about 2.50% nickel, and about 0.50% to about 1.25% silicon.

3 . The alloy steel composition of claim 1 , consisting essentially of:
about 0.26% to about 0.29% carbon, about 2.50% to about 2.80% chromium, about 0.85% to about 1.05% molybdenum, about 0.05% to about 0.15% vanadium, about 0.50% to about 0.80% manganese, about 0.90% to about 1.20% nickel, and about 0.90% to about 1.10% silicon.

4 . The alloy steel composition of claim 1 , wherein the composition comprises about 0.005% sulfur or less, about 0.15% copper or less, and/or about 0.015% aluminum or less.

5 . The alloy steel composition of claim 1 , wherein the composition is substantially void of any tungsten, cobalt, titanium, and/or niobium.

6 . The alloy steel composition of claim 1 , consisting essentially of:
about 0.28% carbon, about 2.52% chromium, about 0.91% molybdenum, about 0.06% vanadium, about 0.62% manganese, about 0.95% nickel, about 0.96% silicon, about 0.01% copper, about 0.002% phosphorous, about 0.004% sulfur, about 0.006% nitrogen, and about 0.014% aluminum.

7 . The alloy steel composition of claim 1 , consisting essentially of:
about 0.27% carbon, about 2.74% chromium, about 0.95% molybdenum, about 0.05% vanadium, about 0.58% manganese, about 1.00% nickel, about 1.00% silicon, about 0.15% copper, about 0.008% phosphorous, about 0.001% sulfur, about 0.005% nitrogen, and about 0.015% aluminum.

8 . The alloy steel composition of claim 1 , wherein the composition has at least one of the following properties:
an ultimate tensile strength of about 200 ksi or more; a yield strength at 0.2% offset of about 170 ksi or more; an elongation to failure of about 10% or more; an impact toughness as measured by a Charpy V-notch test @−40° C. of about 20 ft-lbs or more; or a Hardness Rockwell C-scale of about 45 or more.

9 . The alloy steel composition of claim 1 , wherein the composition has at least one of the following properties:
an ultimate tensile strength of about 230 ksi or more; a yield strength at 0.2% offset of about 180 ksi or more; an elongation to failure of about 11% or more; an impact toughness as measured by a Charpy V-notch test @−40° C. of about 24 ft-lbs or more; or a Hardness Rockwell C-scale of about 45 or more.

10 . The alloy steel composition of claim 8 , further comprising a mixture of epsilon nano-carbides having a length of about 100nm to about 150nm in a matrix of martensite, which may optionally comprise a minor fraction of bainite.

11 . The alloy steel composition of claim 1 , wherein the composition is substantially void of any typical tool-steel alloy carbides selected from the group consisting of M 23 C 6, M 2 C, and M 6 C carbides.

12 . A bomb component comprising the alloy steel composition of claim 1 .

13 . An ingot having a solidified volume, comprising the alloy steel composition of claim 1 .

14 . A method of thermally processing the alloy steel composition of claim 1 , comprising:
a. austenitizing a sample of the alloy steel composition by heating the sample to an austenitizing temperature that is above a critical temperature to form an austenite mixture; b. lowering the austenite mixture to a temperature below a martensitic-forming temperature to provide an austenitized alloy steel composition; and c. tempering the austenitized alloy steel composition, comprising:
i. heating the austenitized alloy steel composition to a tempering temperature, which is in a tempering temperature range that is less than about 500° F. (260° C.) but greater than about 350° F. (177° C.);
ii. maintaining the alloy steel composition in the tempering temperature range for a first duration that is dependent upon a thickness and a length of the sample of the alloy steel composition; and
iii. lowering the alloy steel composition to an ambient temperature.

15 . The method of claim 14 , wherein the critical temperature is about 1750° F. (954° C.) or higher; and wherein the martensitic-forming temperature is about 150° F. (66° C.) or lower.

16 . The method of claim 14 , wherein the austenitizing temperature is at or above a carbide dissolution temp of about 1825° F. (996° C.).

17 . The method of claim 14 , wherein austenitizing the sample of the alloy steel composition further comprises:
i. heating the alloy steel composition to the austenizing temperature, which is in an austenitizing temperature range from about 1825° F. (996° C.) to about 1875° F. (1024° C.), at a rate of about 300° F. (149° C.) per hour or less; ii. maintaining the alloy steel composition in the austenitizing temperature range for a second duration that is dependent upon the thickness and the length of the sample of the alloy steel composition; and iii. quenching the alloy steel composition from the austenizing temperature range to a temperature of about 150° F. (66° C.) or less in liquid quenchant selected from the group consisting of water, an aqueous solution, an oil, a polymer liquid, and combinations thereof.

18 . The method of claim 14 , further comprising normalizing the sample of the alloy steel composition prior to austenitizing, comprising:
i. heating the alloy steel composition to a normalizing temperature range that is about 1825° F. (996° C.) to about 1875° F. (1024° C.); ii. maintaining the alloy steel composition within the normalizing temperature range for a third duration that is dependent upon the thickness and the length of the sample of the alloy steel composition; and iii. allowing the alloy steel composition to air cool from the normalizing temperature range.

19 . The method of claim 14 , further comprising providing a subcritical treatment to the alloy steel composition prior to austenitizing, comprising:
i. heating the alloy steel composition to a subcritical temperature, which is in a subcritical temperature range from about 1225° F. (663° C.) to about 1275° F. (691° C.), at a rate of about 300° F. (149° C.). per hour or less; ii. maintaining the alloy steel composition within the subcritical temperature range for a fourth duration that is dependent upon the thickness and the length of the sample of the alloy steel composition; and iii. quenching the sample of the alloy steel composition from the subcritical temperature range to about 150° F. (149° C.) or below in a liquid quenchant selected from the group consisting of water, an aqueous solution, an oil, a polymer liquid, and combinations thereof.

20 . The method of claim 14 , wherein lowering the alloy steel composition to an ambient temperature is performed by air cooling.

Assignees

• Us Gov Air Force
• Us Gov Air Force

Inventors

• Abrahams Rachel Ann

Classifications

• C21D2211/008

  Martensite · CPC title

• C21D1/60

  Aqueous agents · CPC title

• C21D2211/001

  Austenite · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/001

  containing N · CPC title