Flash tempering process and apparatus

Abstract

A method for tempering a workpiece is provided. The method includes providing a ferrous alloy workpiece having a martensite and/or bainite phase therein, heating at least a portion of the workpiece to a preselected temperature and then cooling the workpiece to a lower temperature. The preselected temperature is below the austensizing temperature of the alloy and the heating is accomplished in no more than 60 seconds. One embodiment of the present invention heats the workpiece using resistance heating.

1 . A method for tempering a workpiece, said method comprising the steps of: 
 providing a ferrous alloy workpiece, said workpiece having a martensite and/or bainite phase therein;    heating at least a portion of said workpiece to a preselected temperature which is below the austenizing temperature of said ferrous alloy, wherein said heating is accomplished in no more than 60 seconds; and    cooling said workpiece to a temperature which is below the preselected temperature.    
   
   
       2 . The method of  claim 1 , wherein the heating of said workpiece is accomplished in no more than 30 seconds.  
   
   
       3 . The method of  claim 1 , wherein said heating is accomplished by resistance heating.  
   
   
       4 . The method of  claim 1 , wherein said heating is accomplished by induction heating.  
   
   
       5 . The method of  claim 1 , wherein said preselected temperature is above the martensite start temperature for said alloy.  
   
   
       6 . The method of  claim 1 , wherein the step of heating is carried out on only a portion of said workpiece whereby said workpiece is selectively tempered.  
   
   
       7 . The method of  claim 1 , wherein said workpiece has a thickness which is no greater than 5 mm.  
   
   
       8 . The method of  claim 1 , wherein the tempering reduces the initial tensile strength of said workpiece by at least 15%.  
   
   
       9 . The method of  claim 1 , wherein said cooling comprises contacting said workpiece with a fluid.  
   
   
       10 . The method of  claim 1 , wherein a quenchant fluid contacts said workpiece during at least a part of the time of said heating.  
   
   
       11 . A method for tempering a workpiece, said method comprising the steps of: 
 providing a ferrous alloy workpiece, said workpiece having a martensite and/or bainite phase therein;    determining the amount of thermal energy required to heat a preselected volume of said workpiece to a preselected temperature which is below the austenizing temperature of said ferrous alloy;    inputting said amount of thermal energy into said volume of said workpiece; and    cooling said workpiece to a temperature below the preselected temperature.    
   
   
       12 . The method of  claim 11 , wherein said preselected volume comprises the entire volume of said workpiece.  
   
   
       13 . The method of  claim 11 , wherein said preselected volume comprises a portion of the volume of said workpiece.  
   
   
       14 . The method of  claim 11 , wherein inputting said amount of thermal energy into said volume is accomplished in no more than 30 seconds.  
   
   
       15 . The method of  claim 11 , wherein the step of inputting said amount of thermal energy comprises resistance heating said preselected volume.  
   
   
       16 . The method of  claim 11 , wherein said preselected temperature is above the martensite start temperature for said alloy.  
   
   
       17 . The method of  claim 11 , wherein the thickness of said preselected volume of said workpiece is no greater than 5 mm.  
   
   
       18 . The method of  claim 11 , wherein the tempering reduces the initial tensile strength of said workpiece by at least 15%.  
   
   
       19 . An apparatus for tempering a workpiece, said apparatus comprising: 
 a support for receiving a workpiece of a ferrous alloy material having a martensite and/or bainite phase;    a heater for heating said workpiece; and    a controller for controlling said heater so that said workpiece is heated to a preselected temperature which is below the austenizing temperature of said ferrous alloy, wherein said heating is accomplished in no more than 60 seconds.    
   
   
       20 . The apparatus of  claim 19 , further comprising a cooling system, said cooling system operative to said workpiece to a temperature below the preselected temperature.