Method of making high strength bainite article, and article made thereby

Abstract

A bainite phase is formed in a body of a ferrous alloy by heating the workpiece to a temperature above an austenizing temperature of the alloy and thereafter contacting the workpiece with a quenching medium. Heat is input to the workpiece during at least a portion of the time it is in contact with the quenching medium. The quenching medium and/or the source of heat are regulated so that they work in combination to maintain the workpiece at a holding temperature which is no more than 350° C. but above the temperature at which the martensite phase forms in the alloy. After maintaining the alloy at the holding temperature for a predetermined period of time, it is cooled to ambient. Also disclosed are systems for implementing the method.

1 . A method for preparing a body of a ferrous alloy containing a high percentage of a bainite phase, said method comprising the steps of: 
 providing a workpiece comprised of a ferrous alloy;    heating said workpiece to a temperature above an austenizing temperature of said alloy; and thereafter    contacting said workpiece with a quenching medium;    inputting heat to said workpiece during at least a portion of the time said workpiece is in contact with said quenching medium so that the combination of said heat which is input, and said quenching medium cooperate to maintain said workpiece at a holding temperature which is no more than 350° C. but above the martensite phase formation temperature of said alloy;    maintaining said workpiece at said holding temperature for a period of time sufficient to form a bainite phase therein; and thereafter    cooling the workpiece to an ambient temperature.    
     
     
         2 . The method of  claim 1 , wherein said workpiece is held at a combination of said holding temperature and said time so as to form a lower bainite phase therein.  
     
     
         3 . The method of  claim 1 , wherein the thickness of said workpiece is no greater than 5 millimeters.  
     
     
         4 . The method of  claim 1 , wherein the thickness of said workpiece is no greater than 3 millimeters.  
     
     
         5 . The method of  claim 1 , wherein the step of inputting heat to said workpiece comprises flowing an electrical current through said workpiece so as to resistively heat said workpiece.  
     
     
         6 . The method of  claim 1 , wherein the step of heating said workpiece to a temperature above an austenizing temperature comprises flowing an electrical current through said workpiece so as to resistively heat said workpiece.  
     
     
         7 . The method of  claim 1 , wherein the step of contacting said workpiece with a quenching medium comprises contacting said workpiece with a liquid medium.  
     
     
         8 . The method of  claim 1 , wherein the step of contacting said workpiece with a quenching medium comprises contacting said workpiece with a gaseous quenching medium.  
     
     
         9 . The method of  claim 1 , wherein the step of contacting said workpiece with a quenching medium comprises immersing said workpiece in said quenching medium.  
     
     
         10 . The method of  claim 1 , wherein the step of contacting said workpiece with a quenching medium comprises spraying said quenching medium onto said workpiece.  
     
     
         11 . The method of  claim 1 , including the further step of measuring the temperature of said workpiece while it is in contact with said quenching medium and said heat is being input thereinto.  
     
     
         12 . The method of  claim 11 , including the further step of controlling the input of heat and/or a parameter of said quenching medium in response to the temperature of said workpiece.  
     
     
         13 . The method of  claim 1 , including the further step of carrying out a forming operation on said workpiece prior to the step of heating said workpiece to a temperature above said austenizing temperature.  
     
     
         14 . The method of  claim 1 , including the further step of carrying out a forming operation on said workpiece after it has been raised to said temperature above said austenizing temperature but before it is maintained at said holding temperature.  
     
     
         15 . The method of  claim 1 , including the further step of carrying out a forming operation on said workpiece while it is maintained at said holding temperature.  
     
     
         16 . The method of  claim 1 , including the further step of carrying out a forming operation on said workpiece after said input of heat is terminated.  
     
     
         17 . The method of  claim 1 , wherein the step of inputting heat to said workpiece comprises inductively heating said workpiece.  
     
     
         18 . An article made by the method of  claim 1 .  
     
     
         19 . An apparatus for preparing a body of a ferrous alloy having a high percentage of a bainite phase, said system comprising: 
 a quenchant delivery system operable to deliver a quenchant fluid to a workpiece;    a heater operable to heat the workpiece during at least part of the time the quenchant delivery system is delivering said quenchant to the workpiece; and    a controller for controlling at least one of said quenchant delivery system and said heater, so that said quenchant delivery system and said heater cooperate to maintain the workpiece at a preselected temperature.    
     
     
         20 . The apparatus of  claim 1 , further including a temperature sensor for generating a signal corresponding to the temperature of said workpiece, said temperature sensor being further operable to communicate said signal to the controller.