High carbon steel wire with bainitic structure for spring and other cold-formed applications

Abstract

According to the present invention, there is disclosed a heat treated high carbon or alloy steel wire and method of heat-treating the wire. The wire is produced by the steps of initially heating the high carbon or alloy steel wire to a temperature of about 1600 degrees F. to about 1800 degrees F. for between 10 seconds and 2 minutes; rapidly cooling the wire to an intermediate point temperature of between 400 to about 1000 degrees F.; holding the wire at the intermediate point temperature for about 2 minutes to about 40 minutes; and cooling the resulting wire to ambient temperature.

1 . A method of heat-treating a high carbon or alloy steel wire comprising the steps of: 
 a. initially heating the high carbon or alloy steel wire to a temperature of about 1600 degrees F. to about 1800 degrees F.;    b. rapidly cooling the wire to an intermediate point temperature of between 400 to about 1000 degrees F.;    c. holding the wire at the intermediate point temperature for about 2 minutes to about 40 minutes; and    d. cooling the resulting heat treated wire to ambient temperature.    
     
     
         2 . The method of  claim 1  wherein the step of initially heating the wire to a temperature of between 1625 degrees F. and 1700 degrees F.  
     
     
         3 . The method of  claim 1  wherein the step of in-process cooling the wire includes cooling the wire to an intermediate point temperature of between 550 and 950 degrees F.  
     
     
         4 . The method of  claim 4  wherein the step of in-process cooling the wire includes cooling the wire to an intermediate point temperature of about 650 degrees F.  
     
     
         5 . The method of  claim 1  wherein the step of initially heating high carbon or alloy steel is for between 10 seconds and 2 minutes.  
     
     
         6 . The method of  claim 1  wherein the step of wire holding the wire at the intermediate temperature is for between 10 and 20 minutes for complete lower bainitic transformation.  
     
     
         7 . The method of  claim 1  wherein the resulting wire has a fully lower bainitic microstructure and a tensile strength of between 160 and 290 ksi.  
     
     
         8 . The method of  claim 7  wherein the resulting wire has a fully lower bainitic microstructure and a tensile strength of between 200 and 270 ksi.  
     
     
         9 . The method of  claim 1  wherein the resulting wire has a fully lower bainitic microstructure and a yield strength of between 130 and 242 ksi.  
     
     
         10 . The method of  claim 1  wherein the resulting wire has a hardness of between 32 and 56 Rockwell C.  
     
     
         11 . The method of  claim 1  wherein the resulting wire has a high ductility as measured by reduction in area of about 35% to about 60%.  
     
     
         12 . The method of  claim 1  wherein the resulting wire adapted for forming a coil spring and wire forms.  
     
     
         13 . A wire high carbon steel, heat treated wire comprising; 
 a high carbon steel, heat treated wire having a lower bainitic microstructure and a tensile strength of between 160 and 290 ksi, a yield strength of between 130 and 142 ksi and a high ductility as measured by reduction in area of about 35% to about 60%.    
     
     
         14 . The wire of  claim 13  wherein the wire is adapted for forming a coil spring or wire form.  
     
     
         15 . The wire of  claim 13  wherein the wire has a tensile strength of between 200 and 270 ksi, a yield strength of between 175 and 230 ksi and a high ductility as measured by reduction in area of about 35% to about 60%.  
     
     
         16 . A heat treated high carbon or alloy steel wire produced by the process of heat-treating the high carbon or alloy steel wire comprising the steps of: 
 a. initially heating the high carbon or alloy steel wire to a temperature of about 1600 degrees F. to about 1800 degrees F.;    b. rapidly cooling the wire to an intermediate point temperature of between 400 to about 1000 degrees F.;    c. holding the wire at the intermediate point temperature for about 2 minutes to about 40 minutes; and    d. cooling the resulting wire to ambient temperature.    
     
     
         17 . The wire of  claim 16  including the step of initially heating the wire to a temperature of between 1625 degrees F. and 1700 degrees F.  
     
     
         18 . The wire of  claim 16  wherein the step of in-process cooling the wire includes cooling the wire to an intermediate point temperature of between 550 and 950 degrees F.  
     
     
         19 . The wire of  claim 16  wherein the step of initially heating high carbon or alloy steel is for between 10 seconds and 2 minutes.  
     
     
         20 . The wire of  claim 16  wherein the step of wire holding the wire at the intermediate temperature is for between 10 and 20 minutes for complete lower bainitic transformation.