Power transmission shaft and method for producing same

Abstract

The present invention provides a power transmission shaft that is capable of eliminating the usual tempering step thereby reducing the production cost, is capable of realizing an inline production process of the shaft, and has higher strength. The invention also provides a method for producing the power transmission shaft. The power transmission shaft is composed of a carbon steel having a carbon content of from 0.30 to 0.48 wt % and of a surface hardened layer 4 formed by high frequency quenching. The surface hardened layer 4 has a tempering-effected portion subjected to tempering using heat generated by external force applied after quenching. The residual stress of the portion subjected to tempering by applying external force is equal to or less than −800 MPa.

1 . A power transmission shaft comprising:
 a carbon steel having a carbon content of from 0.30 to 0.48 wt %; and   a surface hardened layer formed by high frequency quenching,   
     wherein the surface hardened layer has a tempering-effected portion subjected to tempering using heat generated by external force applied after quenching. 
   
   
       2 . The power transmission shaft according to  claim 1 , further comprising a notched portion subjected to tempering by applying external force. 
   
   
       3 . The power transmission shaft according to  claim 1 , wherein the portion subjected to tempering by applying external force has a residual stress of equal to or less than −800 MPa. 
   
   
       4 . A method for producing a power transmission shaft comprising:
 subjecting a carbon steel having a carbon content of from 0.30 to 0.48 wt % to high frequency quenching; and   subjecting the carbon steel to tempering using heat generated by applying external force after quenching.   
   
   
       5 . The power transmission shaft according to  claim 2 , wherein the portion subjected to tempering by applying external force has a residual stress of equal to or less than −800 MPa.