High Temperature Bolt Material

Abstract

A high temperature bolt material, characterized in that it is a ferrite steel comprising 8 wt % or more of Cr and having a tempered martensite structure and can be used in a high temperature region of higher than 500° C.; and a method for producing the high temperature bolt material which comprises subjecting the above-mentioned steel material to a heat treatment comprising a quenching or normalizing at a temperature of 1000° C. or higher and then to a tempering at a temperature of 730° C. or higher. The above ferrite steel high temperature bolt material is excellent in characteristics of the resistance to stress relaxation.

1 . A high temperature bolt material, which is a ferrite steel comprising 8 wt % or more of Cr and having a tempered martensite structure, not containing Ni and Mo, and usable in a high temperature region of over 500° C. 
     
     
         2 . A manufacturing method of the high temperature bolt material of  claim 1 , having a composition composed of, by mass %, Cr: 8.0% or more, C: 0.04 to 0.2%, Si: 0.01 to 0.9% Mn: 0.3 to 1.5%, W: 4.0% or less V: 0.02 to 0.35%, Nb: 0.01 to 0.2%, Co: 4.0% or less, Al: 0.01% or less, N: 0.002 to 0.15%, B: 0.02% or less, and balance of Fe. 
     
     
         3 . A manufacturing method for the high temperature bolt material of  claim 1  which comprises quenching or normalizing a steel material containing Cr by 8 wt % or more at a temperature of 1000° C. or more, and then tempering at a temperature of 730° C. or more. 
     
     
         4 . A manufacturing method for the high temperature bolt material of  claim 2  which comprises quenching or normalizing a steel material containing Cr by 8 wt % or more at a temperature of 1000° C. or more, and then tempering at a temperature of 730° C. or more.