Quench hardened steel

Abstract

Disclosed is a hardenable steel composition, hardened steel components made from the same, and methods for forming the same. The steel contains relatively high levels of molybdenum in comparison to chromium, silicon and manganese, with the molybdenum providing an excellent combination of hardness and impact strength in the hardened steel. The steel can be cold formed then reheat-quench hardened with water as the quenching agent with no cracking and optionally no tempering. The steels formed have Vickers hardness levels of over 630 Hv10 (e.g. over 700 Hv10), and impact strengths of over 3 J/cm2 (e.g. over 20 J/cm2).

1 . A hardenable steel composition consisting of the following, in terms of weight percent: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   C 
                   0.36-0.55%, 
                 
                     
                   Mn 
                    0.1-0.7%, 
                 
                     
                   Si 
                     0-0.7%, 
                 
                     
                   Mo 
                    0.2-1.9%, 
                 
                     
                   Al 
                   ≤0.2% (not including 0%), 
                 
                     
                   Cr 
                   optionally ≤1%, 
                 
                     
                   Ni 
                   optionally ≤2%, 
                 
                     
                   Cu 
                   optionally ≤1%, 
                 
                     
                   Nb 
                   optionally ≤0.1%, 
                 
                     
                   Ti 
                   optionally ≤0.2%, 
                 
                     
                   V 
                   optionally ≤0.2%, 
                 
                     
                   B 
                   optionally ≤0.01%, 
                 
                     
                   W 
                   optionally ≤1%, and 
                 
                     
                   Co 
                   optionally ≤1%, 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       wherein
 % Mo≥% Cr/2 (when Cr is present), 
 % Mo≥% Mn/2, and 
 0.4≤% Mn+% Cr+% Mo≤2 
 
       the balance being iron, residual contents and unavoidable impurities. 
     
     
         2 . The hardenable steel composition of  claim 1 , wherein C is used at levels of 0.38-0.52%. 
     
     
         3 . The hardenable steel composition of  claim 1 , wherein Si is used at levels of 0.01-0.5%. 
     
     
         4 . The hardenable steel composition of  claim 1 , wherein Mn is used at levels of 0.10-0.50%. 
     
     
         5 . The hardenable steel composition of  claim 1 , wherein Cr is used at levels of 0-0.5%. 
     
     
         6 . The hardenable steel composition of  claim 1 , wherein Mo is used at levels of 0.2-1.5%. 
     
     
         7 . The hardenable steel composition of  claim 1 , wherein
 % Mo≥% Cr (when Cr is present)   % Mo≥% Mn, and   0.4≤% Mn+% Cr+% Mo≤2.   
     
     
         8 . The hardenable steel composition of  claim 1 , wherein Ni is optionally present at levels of ≤1%. 
     
     
         9 . The hardenable steel composition of  claim 1 , having the following composition: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Al 
                   0.01-0.1%, 
                 
                     
                   Ti 
                   optionally 0.001-0.05%, 
                 
                     
                   Nb 
                   optionally 0.001-0.05%, 
                 
                     
                   V 
                   optionally ≤0.15%, 
                 
                     
                   Cu 
                   optionally ≤0.1, 
                 
                     
                   Ni 
                   optionally ≤0.1, 
                 
                     
                   B 
                     0-0.003%, 
                 
                     
                   W 
                   optionally ≤0.2%, 
                 
                     
                   Co 
                   optionally ≤0.2%, 
                 
                     
                   P 
                   ≤0.020%, 
                 
                     
                   S 
                   ≤0.020%, 
                 
                     
                   N 
                   ≤0.006%, 
                 
                     
                   H 
                   ≤0.0002%, 
                 
                     
                   O 
                   ≤0.005%, 
                 
                     
                   Ca 
                   ≤0.01, and 
                 
                     
                   REM 
                   ≤0.1%. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         10 . The hardenable steel composition of  claim 1 , wherein the steel contains Nb at levels of 0.005-0.02%. 
     
     
         11 . A hardenable steel that is capable of being reheat-quench hardened to form a steel satisfying the following equation:
     V   J +( H   X   *Hv 10)> A   X      
       wherein
 V J  is the Charpy V impact strength in J/cm 2  at 20° C., 
 Hv10 is the Vickers Hardness, 
 A X =95, and 
 H X =0.125. 
 
     
     
         12 . The hardenable steel of  claim 11 , wherein the steel has a composition as defined in  claim 1 . 
     
     
         13 . A component formed from the hardenable steel composition of  claim 1 , wherein at least a region of the component has been reheat-quench hardened to form a hardened region. 
     
     
         14 . The component of  claim 13 , wherein the Vickers hardness of the hardened region is ≥630 Hv10, and the Charpy V impact strength of the hardened region is ≥3 J/cm 2  at 20° C. 
     
     
         15 . The component of  claim 13 , wherein the hardened region satisfies the following:
     V   J +( H   X   *Hv 10)> A   X      
       wherein
 V J  is the Charpy V impact strength in J/cm 2  at 20° C., 
 Hv10 is the Vickers Hardness, 
 A X =95, and 
 H X =0.125. 
 
     
     
         16 . The component of  claim 13 , wherein the entire component has been reheat-quench hardened. 
     
     
         17 . A method for producing hardened steel, comprising the steps of:
 a. providing a component formed from a hardenable steel composition as defined in  claim 1 ;   b. heating at least a region of the component to a temperature (T S ) above A c3 ;   c. quenching said region using a quenching fluid to form a hardened region; and   d. optionally tempering the hardened region.   
     
     
         18 . The method of  claim 17 , wherein the Vickers hardness of the hardened region is ≥630 Hv10, and the Charpy V impact strength of the hardened region is ≥3 J/cm 2  at 20° C. 
     
     
         19 . The method of  claim 17 , wherein the hardened region satisfies the following:
     V   J +( H   X   *Hv 10)> A   X      
       wherein
 V J  is the Charpy V impact strength in J/cm 2  at 20° C., 
 Hv10 is the Vickers Hardness, 
 A X =95, and 
 H X =0.125.