High Strength, High Impact Toughness Steel Alloy, an Article of Manufacture Made Therefrom, and a Method for Making the Same

A steel alloy consisting essentially of, in weight percent:

• C
• about 0.22-about 0.25
• Mn
• about 0.1 max.
• Si
• about 0.1 max.
• P
• about 0.005 max.
• S
• about 0.001 max.
• Cr
• about 1.3-about 1.7
• Mo
• about 1.3-about 1.8
• V
• about 0.2-about 0.4
• Ni
• about 3.2-about 3.7
• Nb
• about 0.01-about 0.03
• Cu
• about 0.10 max.
• Al
• about 0.02 max.
• the balance being iron, impurities, and incidental amounts of residual elements that do not adversely affect the basic and novel properties provided by the alloy.

An article of manufacture made from a steel alloy consisting essentially of, in weight percent:

• C
• about 0.21-about 0.27
• Mn
• about 0.1 max.
• Si
• about 0.1 max.
• P
• about 0.005 max.
• S
• about 0.002 max.
• Cr
• about 1.2-about 1.8
• Mo
• about 1.1-about 1.9
• V
• about 0.2-about 0.4
• Ni
• about 3.0-about 3.8
• Nb
• about 0.005-about 0.03
• Cu
• about 0.10 max.
• Al
• about 0.02 max.
• the balance being iron, impurities, and incidental amounts of residual elements that do not adversely affect the basic and novel properties provided by the alloy, wherein the article is characterized by having a room temperature yield strength of at least 150 ksi in the hardened and tempered condition, and wherein the article is further characterized by having a Charpy V-notch impact toughness of at least at least 100 ft-lbs, when tested at a temperature of −40° C.

A method of making an article of manufacture from a steel alloy consisting essentially of, in weight percent:

• C
• about 0.21-about 0.27
• Mn
• about 0.1 max.
• Si
• about 0.1 max.
• P
• about 0.005 max.
• S
• about 0.002 max.
• Cr
• about 1.2-about 1.8
• Mo
• about 1.1-about 1.9
• V
• about 0.2-about 0.4
• Ni
• about 3.0-about 3.8
• Nb
• about 0.005-about 0.03
• Cu
• about 0.10 max.
• Al
• about 0.02 max.
• the balance being iron, impurities, and incidental amounts of residual elements that do not adversely affect the basic and novel properties provided by the alloy, said method comprising the steps of
• providing an intermediate form of said alloy;
• hot rolling the intermediate form from a temperature of about 1950° F. down to a temperature of about 1700° F. to provide said article of manufacture;
• annealing the article of manufacture at a temperature of about 1600° F. to about 1700° F. for about 1 to about 4 hours, followed by
• cooling the annealed article of manufacture to about 70° F.;
• followed by
• tempering the article of manufacture to final hardness and strength by heating at a temperature of 1110-1180° F. for about 2 to about 8 hours;
• and then
• cooling the article of manufacture to about 70° F.