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

Abstract

A steel alloy is disclosed. The alloy contains 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 of the alloy is 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 and method of making same are also disclosed.

1 . 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 
                   1.1-about 1.9 
                 
                     
                   V 
                   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. 
       
     
     
         2 . The steel alloy claimed in  claim 1  wherein carbon is about 0.22% to about 0.25%. 
     
     
         3 . The steel alloy claimed in  claim 1  wherein chromium is about 1.3% to about 1.8%. 
     
     
         4 . The steel alloy claimed in  claim 3  wherein chromium is about 1.2% to about 1.7%. 
     
     
         5 . The steel alloy claimed in  claim 1  wherein nickel is about 3.2% to about 3.7%. 
     
     
         6 . The steel alloy claimed in  claim 1  wherein niobium is about 0.01% to about 0.03%. 
     
     
         7 . 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 
                   1.3-about 1.8 
                 
                     
                   V 
                   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. 
       
     
     
         8 . An article of manufacture made from the steel alloy as claimed in  claim 1  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. 
     
     
         9 . The article as claimed in  claim 8  wherein the alloy has a grain size that is not coarser than ASTM Grain Size No. 7 in the hardened-and-tempered condition. 
     
     
         10 . The article of manufacture as claimed in  claim 8  wherein the article is a gun barrel. 
     
     
         11 . A method of making an article of manufacture from the steel alloy as claimed in  claim 1 , said method comprising the steps of
 providing an intermediate form of said steel 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.   
     
     
         12 . The method as claimed in  claim 11  wherein the tempering step is carried out by heating the article at a temperature of about 1160° F. to about 1175° F. for about 3 hours to about 5 hours.