Cast shaped article made from high strength, precipitation-hardenable stainless steel and a process for making same

Abstract

A shaped article which is manufactured by casting in air or under inert-gas shrouding at atmospheric pressure is disclosed. The shaped article provides a superior combination of high strength, hardness, ductility, and corrosion resistance compared to the known air-castable stainless steels. A cast article in accordance with this invention is made from a high strength, castable, stainless steel alloy having the following weight percent composition. C  0.1 max. Mn   2 max. Si   1 max. P 0.05 max. S 0.05 max. Cr 9-13 Ni 4-8  Mo 4-8  Co 8-16 N 0.1 max. The balance of the alloy is essentially iron and the usual impurities. A process for making such an article is also described.

What is claimed is:  
     
         1 . A cast, shaped article that is made from a high strength, precipitation-hardenable stainless steel alloy consisting essentially of, in weight percent, about  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                    0.1 max. 
                 
                     
                   Mn 
                     2 max. 
                 
                     
                   Si 
                     1 max. 
                 
                     
                   P 
                   0.05 max. 
                 
                     
                   S 
                   0.05 max. 
                 
                     
                   Cr 
                   9-13 
                 
                     
                   Ni 
                   4-8  
                 
                     
                   Mo 
                   4-8  
                 
                     
                   Co 
                   8-16 
                 
                     
                   N 
                    0.1 max. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the balance being essentially iron and the usual impurities.  
     
     
         2 . A shaped article as set forth in  claim 1  which provides a room temperature yield strength of at least about 220 ksi in the cast and heat treated condition.  
     
     
         3 . A shaped article as set forth in  claim 1  in which the precipitation hardenable stainless steel alloy contains up to about 1% niobium.  
     
     
         4 . A shaped article as set forth in  claim 1  in which the precipitation hardenable stainless steel alloy contains up to about 0.02% boron.  
     
     
         5 . A shaped article as set forth in  claim 1  in which the precipitation hardenable stainless steel alloy consists essentially of, in weight percent, about  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                   0.025 max. 
                 
                     
                   Mn 
                      1 max. 
                 
                     
                   Si 
                      1 max. 
                 
                     
                   P 
                    0.04 max. 
                 
                     
                   S 
                    0.03 max. 
                 
                     
                   Cr 
                   9.5-12  
                 
                     
                   Ni 
                   5-8 
                 
                     
                   Mo 
                   4-8 
                 
                     
                   Co 
                    8-16 
                 
                     
                   N 
                   0.025 max. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the balance being essentially iron and the usual impurities.  
     
     
         6 . A shaped article as set forth in  claim 5  in which the precipitation hardenable stainless steel alloy contains up to about 1% niobium.  
     
     
         7 . A shaped article as set forth in  claim 5  in which the precipitation hardenable stainless steel alloy contains up to about 0.02% boron.  
     
     
         8 . A shaped article as set forth in  claim 1  in which the precipitation hardenable stainless steel alloy consists essentially of, in weight percent, about  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                   0.015 max. 
                 
                     
                   Mn 
                    0.5 max. 
                 
                     
                   Si 
                    0.5 max. 
                 
                     
                   P 
                    0.03 max. 
                 
                     
                   S 
                    0.01 max. 
                 
                     
                   Cr 
                   10.0-11.5 
                 
                     
                   Ni 
                   5.5-7.5 
                 
                     
                   Mo 
                   5-6 
                 
                     
                   Co 
                    9.5-13.5 
                 
                     
                   N 
                   0.015 max. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the balance being essentially iron and the usual impurities.  
     
     
         9 . A shaped article as set forth in  claim 8  in which the precipitation hardenable stainless steel alloy contains up to about 1% niobium.  
     
     
         10 . A shaped article as set forth in  claim 8  in which the precipitation hardenable stainless steel alloy contains up to about 0.02% boron.  
     
     
         11 . A process for making a shaped article, comprising the steps of: 
 melting a stainless steel alloy having the following composition in weight percent                                                C    0.1 max.         Mn     2 max.         Si     1 max.         P   0.05 max.         S   0.05 max.         Cr   9-13         Ni   4-8          Mo   4-8          Co   8-16         N    0.1 max.                                                      the balance being essentially iron and the usual impurities;    casting the molten alloy into a mold to form a cast article;    allowing the cast article to solidify; and then    heat treating the cast article to age harden the cast article.    
     
     
         12 . A process as set forth in  claim 11  wherein the molten alloy is cast in air.  
     
     
         13 . A process as set forth in  claim 11  wherein the molten alloy is cast under an inert gas atmosphere.  
     
     
         14 . A process as set forth in  claim 11  comprising the step of heat treating the cast article to substantially homogenize the composition and microstructure of the cast article, said homogenization heat treating being performed after the cast article has solidified, but before the cast article is age hardened.  
     
     
         15 . A process as set forth in  claim 14  wherein the homogenization heat treating step comprises the step of heating the cast article at a homogenization temperature of about 2000 to 2300° F. and then cooling the cast article.  
     
     
         16 . A process as set forth in  claim 15  wherein the homogenization heat treating step comprises the step of heating the cast article for about 1 to 4 hours.  
     
     
         17 . A process as set forth in  claim 15  comprising the step of cooling the cast article from the homogenization temperature to about room temperature.  
     
     
         18 . A process as set forth in  claim 11  wherein the age hardening heat treating step comprises the steps of: 
 heating the cast article at an elevated temperature sufficient to substantially completely austenitize the stainless steel alloy;  
 rapidly cooling the cast article to about room temperature; and then  
 heating the cast article at a hardening temperature of about 900 to 1100° F.  
 
     
     
         19 . A process as set forth in  claim 18  wherein the step of austenitizing the stainless steel alloy comprises heating the cast article at a temperature of about 1400 to 2000° F. for at least 30 minutes.  
     
     
         20 . A process as set forth in  claim 18  wherein the step of heating the austenitized alloy comprises the step of heating the austenitized alloy at a temperature of about 950 to 1025° F. to provide a yield strength of at least about 220 ksi.  
     
     
         21 . A process as set forth in  claim 18  or  20  wherein the austenitized alloy is heated for about 1 to 4 hours.  
     
     
         22 . A golf club head made from a high strength, precipitation-hardenable stainless steel alloy consisting essentially of, in weight percent, about  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                    0.1 max. 
                 
                     
                   Mn 
                     2 max. 
                 
                     
                   Si 
                     1 max. 
                 
                     
                   P 
                   0.05 max. 
                 
                     
                   S 
                   0.05 max. 
                 
                     
                   Cr 
                   9-13 
                 
                     
                   Ni 
                   4-8  
                 
                     
                   Mo 
                   4-8  
                 
                     
                   Co 
                   8-16 
                 
                     
                   N 
                    0.1 max. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the balance being essentially iron and the usual impurities, 
 said golf club head having been formed by casting said alloy into a mold, solidifying the alloy, and then heat treating the alloy under conditions of temperature and time sufficient to provide a yield strength of at least about 220 ksi for said golf club head.