Method of induction heating and quenching

Abstract

An induction hardening heat treatment method comprises the steps of induction heating a metal part or component, particularly a part fabricated of a high strength material, and then exposing the part to a sequence or series of partial, intermittent or interrupted quenches. Such intermittent or interrupted quenching achieves the necessary change in surface temperature with time to achieve a martensitic transformation of the surface adjacent metal or material while minimizing surface to core temperature differentials during the process which could result in cracking of the part, especially if it is fabricated of high strength materials.

1 . A method of induction hardening a part or component, comprising the steps of:
 induction heating the part or component,   subjecting the part or component to a first, partial quench,   interrupting said first, partial quench for a first interval,   subjecting the part or component to a second, partial quench,   interrupting said second partial quench for a second interval, and   subjecting the part or component to a third, partial quench.   
     
     
         2 . The method of  claim 1  wherein said first, partial quench is shorter in duration than either said second, partial quench or said third, partial quench. 
     
     
         3 . The method of  claim 1  wherein a surface adjacent region of said part or component undergoes a martensitic transformation during said quenches. 
     
     
         4 . The method of  claim 1  further including the step of determining that a surface adjacent region of said part or component has undergone a martensitic transformation during said quenches. 
     
     
         5 . The method of  claim 1  wherein the part or component is induction heated to at least the austenitic temperature. 
     
     
         6 . The method of  claim 1  wherein said second, partial quench and said second interval are substantially equal in duration. 
     
     
         7 . The method of  claim 1  wherein said duration of said second, partial quench is longer than said first, partial quench and said third, partial quench is longer than said second, partial quench. 
     
     
         8 . A method of induction hardening a metal part, comprising the steps of:
 induction heating said metal part to at least its austenitic temperature,   partially quenching said metal part,   interrupting said partial quenching for a time interval, and   repeating said partial quenching and interrupting steps until a surface adjacent region of said metal part has undergone a martensitic transformation.   
     
     
         9 . The method of induction hardening a metal part of  claim 8  wherein a total of three partial quenching steps are performed. 
     
     
         10 . The method of induction hardening a metal part of  claim 8  wherein a first partial quenching step is shorter in duration than a subsequent partial quenching step. 
     
     
         11 . The method of induction hardening a metal part of  claim 8  wherein a second partial quenching step and a second partial quenching interruption are substantially equal in duration. 
     
     
         12 . The method of induction hardening a metal part of  claim 8  wherein said duration of said partial quenching steps is increased if bainite is detected in said metal part. 
     
     
         13 . The method of induction hardening a metal part of  claim 8  wherein a small differential between a surface temperature and a core temperature of said metal part are maintained during said repeated quenching and interrupting steps whereby stress cracking is essentially eliminated. 
     
     
         14 . A method of induction hardening a metal part comprising the steps of:
 providing an induction heater and induction heating a metal part,   providing a quenching station and partially quenching said metal part at said quenching station in a first quenching partial step,   interrupting said first partial quenching step and holding said metal part for a first dwell period in said quenching station,   further partially quenching said metal part at said quenching station in a second, partial quenching step,   interrupting said second partial quenching step and holding said metal part for a second dwell period in said quenching station, and   further quenching said metal part at said quenching station.   
     
     
         15 . The method of induction hardening a metal part of  claim 14  wherein said first partial quenching step is shorter in duration than a subsequent partial quenching step. 
     
     
         16 . The method of induction hardening a metal part of  claim 14  wherein said second partial quenching step and said second dwell period are substantially equal in duration. 
     
     
         17 . The method of induction hardening a metal part of  claim 14  wherein said duration of said partial quenching steps is increased if bainite is detected in said metal part. 
     
     
         18 . The method of induction hardening a metal part of  claim 14  wherein said metal part is heated to at least its austenitic temperature. 
     
     
         19 . The method of induction hardening a metal part of  claim 14  wherein a small differential between a surface temperature and a core temperature of said metal part are maintained during said repeated quenching and interrupting steps whereby stress cracking is essentially eliminated.