High strength, high toughness steel alloy

Abstract

A high strength, high toughness steel alloy is disclosed. The alloy has the following weight percent composition. Element C 0.30-0.47 Mn 0.8-1.3 Si 1.5-2.5 Cr 1.5-2.5 Ni 3.0-5.0 Mo + ½ W 0.7-0.9 Cu 0.70-0.90 Co  0.01 max. V + ( 5/9) × Nb 0.10-0.25 Ti 0.005 max. Al 0.015 max. Fe Balance Included in the balance are the usual impurities found in commercial grades of steel alloys produced for similar use and properties including not more than about 0.01% phosphorus and not more than about 0.001% sulfur. Also disclosed is a hardened and tempered article that has very high strength and fracture toughness. The article is formed from the alloy having the broad weight percent composition set forth above. The alloy article according to this aspect of the invention is further characterized by being tempered at a temperature of about 500° F. to 600° F.

1 . A high strength, high toughness steel alloy having good temper resistance, said alloy comprising, in weight percent, about: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   C 
                   0.30-0.47 
                 
                     
                   Mn 
                   0.8-1.3 
                 
                     
                   Si 
                   1.5-2.5 
                 
                     
                   Cr 
                   1.5-2.5 
                 
                     
                   Ni 
                   3.0-5.0 
                 
                     
                   Mo + ½ W 
                   0.7-0.9 
                 
                     
                   Cu 
                   0.70-0.90 
                 
                     
                   Co 
                    0.01 max. 
                 
                     
                   V + ( 5/9) × Nb 
                   0.10-0.25 
                 
                     
                   Ti 
                   0.005 max. 
                 
                     
                   Al 
                   0.015 max. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         the balance being iron and usual impurities wherein phosphorus is restricted to about 0.01% max. and sulfur is restricted to not more than about 0.001% max., and wherein
   2≦(% Si+% Cu)/(% V+(5/9) x % Nb)≦34.