Method for heat treatment of columnar work

Abstract

The present invention relates to a method for heat treatment of a columnar work. In order to provide the method for heat treatment of a columnar work being able to attain a high productivity, a reduction of cost, and an improvement of quality, as compared with the prior art, the method for heat treatment of a columnar work of the present invention includes a quench-hardening step and a tempering step being carried out after the quench-hardening step, the quench-hardening step includes a first quench-hardening step and a second quench-hardening step being carried out after the first quench-hardening step, the entire region of the columnar work from an outer circumferential surface to a core thereof, or a partial region thereof, is heated up to a temperature not lower than a transformation temperature Ac 3 , and then, the work is quench-hardened.

1 . A method for heat treatment of a columnar work, in which a heat treatment of a columnar work made of a medium-carbon alloy steel is carried out, characterized in that:
 the method comprises a quench-hardening step and a tempering step being carried out after the quench-hardening step:   the quench-hardening step includes a first quench-hardening step and a second quench-hardening step being carried out after the first quench-hardening step;   the first quench-hardening step is a quench-hardening step in which an entire region of the columnar work being from an outer circumferential surface to a core thereof is heated to a temperature not lower than a transformation temperature Ac 3 ;   the second quench-hardening step is a quench-hardening step in which an outer circumferential surface region of the columnar work carried out by the quench-hardening in the first quench-hardening step is merely heated by an induction heating to a temperature not lower than the transformation temperature Ac 3 ; and that   the tempering step is a step for low-temperature tempering to the columnar work carried out by the quench-hardening in the quench-hardening step.   
     
     
         2 . The method for heat treatment of a columnar work according to  claim 1 ,
 wherein the heating in the first quench-hardening step is an induction heating.   
     
     
         3 . The method for heat treatment of a columnar work according to  claim 1 ,
 wherein the heating in the first quench-hardening step is a heating within a furnace.   
     
     
         4 . The method for heat treatment of a columnar work according to  claim 1 ,
 wherein a depth of the outer circumferential surface region, in the second quench-hardening step, is not less than 1/10 of a radius of the columnar work, and not more than ½ of the radius of the columnar work.   
     
     
         5 . The method for heat treatment of a columnar work according to  claim 1 ,
 wherein the columnar work is a pin for an endless track.   
     
     
         6 . The method for heat treatment of a columnar work according to  claim 2 , wherein a depth of the outer circumferential surface region, in the second quench-hardening step, is not less than 1/10 of a radius of the columnar work, and not more than ½ of the radius of the columnar work. 
     
     
         7 . The method for heat treatment of a columnar work according to  claim 3 , wherein a depth of the outer circumferential surface region, in the second quench-hardening step, is not less than 1/10 of a radius of the columnar work, and not more than ½ of the radius of the columnar work. 
     
     
         8 . The method for heat treatment of a columnar work according to  claim 2 , wherein a dimension of the partial region of the columnar work in the radial direction thereof, which region is heated in the first quench-hardening step, is not less than ⅓ of the radius of the columnar work, and is not more than ¾ of the radius of the columnar work. 
     
     
         9 . The method for heat treatment of a columnar work according to  claim 3 , wherein a dimension of the partial region of the columnar work in the radial direction thereof, which region is heated in the first quench-hardening step, is not less than ⅓ of the radius of the columnar work, and is not more than ¾ of the radius of the columnar work. 
     
     
         10 . The method for heat treatment of a columnar work according to  claim 4 , wherein a dimension of the partial region of the columnar work in the radial direction thereof, which region is heated in the first quench-hardening step, is not less than ⅓ of the radius of the columnar work, and is not more than ¾ of the radius of the columnar work. 
     
     
         11 . The method for heat treatment of a columnar work according to  claim 2 , wherein the columnar work is a pin for an endless track. 
     
     
         12 . The method for heat treatment of a columnar work according to  claim 3 , wherein the columnar work is a pin for an endless track. 
     
     
         13 . The method for heat treatment of a columnar work according to  claim 4 , wherein the columnar work is a pin for an endless track.