Method of Making a High Strength, High Toughness, Fatigue Resistant, Precipitation Hardenable Stainless Steel and Product Made Therefrom

Abstract

A process for making a precipitation hardenable stainless steel alloy is described. The process includes the step of melting a martensitic steel alloy having the following composition in weight percent, about Carbon  0.03 max. Manganese  1.0 max. Silicon  0.75 max. Phosphorus 0.040 max. Sulfur 0.020 max. Chromium 10-13 Nickel 10.5-11.6 Titanium 1.5-1.8 Molybdenum 0.25-1.5  Copper  0.95 max. Aluminum  0.25 max. Niobium  0.3 max. Boron 0.010 max. Nitrogen 0.030 max. and the balance being iron and usual impurities. The process also includes the step of adding calcium to the alloy while molten. The calcium combines with available sulfur and oxygen to form calcium base inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof. In a further step, the alloy is processed to remove at least a portion of the calcium base inclusions. The alloy is then solidified. As a result of the process, the alloy has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions.

1 . A method of making a precipitation hardenable, high strength, high toughness, stainless steel alloy to provide improved fatigue strength relative to a rare-earth-treated alloy, said method comprising the steps of:
 melting a martensitic steel alloy having the following composition in weight percent, about   
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Carbon 
                    0.03 max. 
                 
                     
                   Manganese 
                    1.0 max. 
                 
                     
                   Silicon 
                    0.75 max. 
                 
                     
                   Phosphorus 
                   0.040 max. 
                 
                     
                   Sulfur 
                   0.020 max. 
                 
                     
                   Chromium 
                   10-13 
                 
                     
                   Nickel 
                   10.5-11.6 
                 
                     
                   Titanium 
                   1.5-1.8 
                 
                     
                   Molybdenum 
                   0.25-1.5  
                 
                     
                   Copper 
                    0.95 max. 
                 
                     
                   Aluminum 
                    0.25 max. 
                 
                     
                   Niobium 
                    0.3 max. 
                 
                     
                   Boron 
                   0.010 max. 
                 
                     
                   Nitrogen 
                   0.030 max. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and the balance being iron and usual impurities;
 adding calcium to the alloy while molten whereby the calcium combines with available sulfur and oxygen to form calcium-based inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof; 
 processing said alloy to remove at least a portion of said calcium-based inclusions; and then 
 solidifying said alloy; 
 
       whereby after said processing and solidifying steps said alloy contains substantially no rare-earth based inclusions and has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions. 
     
     
         2 . The method as claimed in  claim 1  wherein the melting step comprises vacuum melting the martensitic steel alloy and the adding step is performed during said vacuum melting. 
     
     
         3 . The method as claimed in  claim 2  wherein the processing step comprises vacuum remelting the alloy. 
     
     
         4 . The method as claimed in  claim 1  wherein the processing step comprises vacuum remelting the alloy. 
     
     
         5 . A method of making a precipitation hardenable, high strength, high toughness, stainless steel alloy to provide improved fatigue strength relative to a rare-earth-treated alloy, said method comprising the steps of:
 melting a martensitic steel alloy having the following composition in weight percent, about   
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Carbon 
                    0.02 max. 
                 
                     
                   Manganese 
                    0.25 max. 
                 
                     
                   Silicon 
                    0.25 max. 
                 
                     
                   Phosphorus 
                   0.015 max. 
                 
                     
                   Sulfur 
                   0.010 max. 
                 
                     
                   Chromium 
                   10.5-12.5 
                 
                     
                   Nickel 
                   10.75-11.25 
                 
                     
                   Titanium 
                   1.5-1.7 
                 
                     
                   Molybdenum 
                   0.75-1.25 
                 
                     
                   Copper 
                    0.50 max. 
                 
                     
                   Aluminum 
                   0.050 max. 
                 
                     
                   Niobium 
                   0.050 max. 
                 
                     
                   Boron 
                   0.001-0.005 
                 
                     
                   Nitrogen 
                   0.015 max. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and the balance being iron and usual impurities;
 adding calcium to the alloy while molten whereby the calcium combines with available sulfur and oxygen to form calcium-based inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof; 
 processing said alloy to remove at least a portion of said calcium-based inclusions; and then 
 solidifying said alloy; 
 
       whereby after said processing and solidifying steps said alloy contains substantially no rare-earth based inclusions and has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions. 
     
     
         6 . The method as claimed in  claim 5  wherein the melting step comprises vacuum melting the martensitic steel alloy and the adding step is performed during said vacuum melting. 
     
     
         7 . The method as claimed in  claim 6  wherein the processing step comprises vacuum remelting the alloy. 
     
     
         8 . The method as claimed in  claim 5  wherein the processing step comprises vacuum remelting the alloy. 
     
     
         9 . A method of making a precipitation hardenable, high strength, high toughness, stainless steel alloy to provide improved fatigue strength relative to a rare-earth-treated alloy, said method comprising the steps of:
 melting a martensitic steel alloy having the following composition in weight percent, about   
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Carbon 
                   0.015 max. 
                 
                     
                   Manganese 
                    0.10 max. 
                 
                     
                   Silicon 
                    0.10 max. 
                 
                     
                   Phosphorus 
                   0.010 max. 
                 
                     
                   Sulfur 
                   0.005 max. 
                 
                     
                   Chromium 
                   11.0-12.0 
                 
                     
                   Nickel 
                   10.85-11.25 
                 
                     
                   Titanium 
                   1.5-1.7 
                 
                     
                   Molybdenum 
                   0.9-1.1 
                 
                     
                   Copper 
                    0.25 max. 
                 
                     
                   Aluminum 
                   0.025 max. 
                 
                     
                   Niobium 
                   0.025 max. 
                 
                     
                   Boron 
                   0.0015-0.0035 
                 
                     
                   Nitrogen 
                   0.010 max. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       and the balance being iron and usual impurities;
 adding calcium to the alloy while molten whereby the calcium combines with available sulfur and oxygen to form calcium-based inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof; 
 processing said alloy to remove at least a portion of said calcium-based inclusions; and then 
 solidifying said alloy; 
 
       whereby after said processing and solidifying steps said alloy contains substantially no rare-earth based inclusions and has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions. 
     
     
         10 . The method as claimed in  claim 9  wherein the melting step comprises vacuum melting the martensitic steel alloy and the adding step is performed during said vacuum melting. 
     
     
         11 . The method as claimed in  claim 10  wherein the processing step comprises vacuum remelting the alloy. 
     
     
         12 . The method as claimed in  claim 9  wherein the processing step comprises vacuum remelting the alloy. 
     
     
         13 . The method as claimed in  claim 1  wherein the process is further characterized in that rare earth metal additions are not used to make the alloy. 
     
     
         14 . The method as claimed in  claim 5  wherein the process is further characterized in that rare earth metal additions are not used to make the alloy. 
     
     
         15 . The method as claimed in  claim 9  wherein the process is further characterized in that rare earth metal additions are not used to make the alloy.