Heat-Treatment Process for a Steel

Abstract

A process for inducing a compressive residual stress in a surface region of a steel component, the process comprising a heat treatment having the following steps: (i) providing a component comprising a steel composition; (ii) induction heating at least a part of the component followed by quenching said at least part, wherein the hardness in a surface region of the component is increased; and (iii) subsequently performing a martensite and/or bainite through hardening step to obtain a microstructure comprising martensite and/or bainite.

1 . A heat treatment process for inducing a compressive residual stress in a surface region of a steel component, the process comprising the steps of:
 providing a steel component;   induction heating at least a part of the component followed by quenching the part of the component so as to increase the hardness in a surface region of the component; and   subsequently performing at least one of a martensite through hardening of the component and a bainite through hardening of the component to obtain a microstructure comprising the at least one of martensite and bainite.   
     
     
         2 . The process as claimed in  claim 1 , wherein the step of induction heating includes heating the part of the component is heated to a depth of from about 0.5 mm to about 3 mm. 
     
     
         3 . The process as claimed in  claim 1 , wherein the step of induction heating includes heating the surface of the at least part of the component to a temperature within a range of from about 1000° C. to about 1100° C. 
     
     
         4 . A process for inducing a compressive residual stress in a surface region of a steel component, the process comprising a heat treatment having the following steps:
 providing a steel component;   performing at least one of a martensite through hardening of the component and a bainite through hardening of the component to obtain a microstructure including at least one of martensite and bainite; and   induction heating at least a part of the component followed by quenching the at least part of the component so as to increase the hardness in a surface region of the component.   
     
     
         5 . The process as claimed in  claim 4 , wherein the step of induction heating includes heating the part of the component to a depth of from about 1 mm to about 6 mm. 
     
     
         6 . The process as claimed in  claim 4 , wherein the step of induction heating includes heating the surface of the part of the component to a temperature within a range of from about 900° C. to 1000° C. 
     
     
         7 . The process as claimed in  claim 4 , further comprising the step of tempering the component subsequent to quenching the component. 
     
     
         8 . The process as claimed in  claim 4 , wherein the steel component is formed of one of a medium carbon steel and a high carbon steel. 
     
     
         9 . The process as claimed in  claim 8 , wherein the steel component is formed of a high carbon chromium steel. 
     
     
         10 . The process as claimed in any  claim 4 , wherein the step of induction heating includes one of medium frequency induction heating and high frequency induction heating. 
     
     
         11 . The process as claimed in  claim 10 , wherein the induction heating is performed at a frequency within a range of from about 2 kHz to about 100 kHz. 
     
     
         12 . (canceled) 
     
     
         13 . The process as claimed in  claim 4 , wherein the martensite through hardening step includes austenitising the steel component and subsequently quenching the steel component below the martensite start temperature. 
     
     
         14 . The process as claimed in  claim 13 , wherein the through hardening step includes post-quenching the component to promote further austenite to martensite transformation. 
     
     
         15 . The process as claimed in  claim 14 , wherein the step of induction heating includes tempering the component subsequent to quenching. 
     
     
         16 . The process as claimed in any  claim 4 , wherein the bainite through hardening step includes austenitising the steel, quenching the steel above the martensite start temperature, and subsequently performing an isothermal bainite transformation. 
     
     
         17 . The process as claimed in  claim 16 , wherein the isothermal bainite transformation is performed at a temperature in the range of from about 210° C. to about 240° C. for a duration within a range of from about 2.5 hours to about 20 hours. 
     
     
         18 . The process as claimed in  claim 13 , wherein the steel component is austenitised at a temperature in the range of from about 790° C. to about 890° C. and for a duration within a range from about 20 minutes to about 60 minutes. 
     
     
         19 . The process as claimed in  claim 1 , further comprising the step of a second induction heating of at least a part of the component followed by quenching the at least part of the component, wherein the hardness in a surface region of the component is increased. 
     
     
         20 . The process as claimed in  claim 4 , wherein the process is a non-thermochemical process.