Bolt and Manufacturing Method of Bolt

Abstract

The present invention provides a surface hardening portion 11 that has increased surface hardness and that is applied with a compressive residual stress, at least on the surface of a male screw 10 of a bolt 1. The present invention includes the steps of cutting to form the male screw 10 of the bolt 1, and processing to provide at least on the surface of the male screw 10 of the bolt 1 the surface hardening portion 11 that has increased hardness and that is applied with a compressive residual stress. As a result, the present invention can improve the fatigue resistance of the male screw 10 and the bolt is effective as a bolt to be used in a portion where the male screw 10 is subject to a repetitive stress.

1 . A bolt having a male screw, comprising:
 a surface hardening portion that is disposed at least on the surface of the male screw to increase a surface hardness and to provide a compressive residual stress, wherein   the surface hardening portion is formed by a process in which the particles having a equal or smaller particle size of being capable of passing through a mesh with a mesh size of #150 are projected to at least the surface of the male screw.   
   
   
       2 . (canceled) 
   
   
       3 . A manufacturing method of a bolt having a male screw, comprising:
 cutting to form the male screw; and   processing to provide on at least the surface of the male screw a surface hardening portion that has increased hardness and that is applied with a compressive residual stress, wherein   the processing includes a surface treatment by which the particles having a equal or smaller particle size of being capable of passing through a mesh with a mesh size of #150 are projected to at least the surface of the male screw.   
   
   
       4 . (canceled) 
   
   
       5 . The bolt of  claim 1 , wherein
 the process includes four to six times of the projections.   
   
   
       6 . The bolt of  claim 1 , wherein
 the process includes a projection distance ranging between 500 mm and 750 mm.   
   
   
       7 . The bolt of  claim 3 , wherein
 the processing includes four to six times of the projections.   
   
   
       8 . The bolt of  claim 3 , wherein
 the processing includes a projection distance ranging between 500 mm and 750 mm.