HIGH TENSION BOLT HAVING CHARACTERISTICS OF RESISTANCE TO DELAYED FRACTURE AND ITS PRODUCTION

摘要

PURPOSE:To produce a high tension bolt having resistance to delayed cracking by subjecting a low alloy steel bar material contg. C and Si as essential components to hardening and tempering over the entire section then subjecting only the surface layer to re-tempering treatment and threading. CONSTITUTION:A low alloy steel bar material contg. 0.3-0.6wt% C and >=1.2% Si as essential components is subjected to hardening and tempering over the entire section to finish the tensile strength of the bar material to >=150kgf/mm.<2> then only the surface layer of the bar material is quickly heated by a high frequency induction heating means up to the prescribed high temp. from the above-mentioned tempering treatment. The material is subjected in succession to quick cooling and re-tempering to form a fine pearlite structure. The end of the treated bar material is subjected to threading by rolling and, if necessary, said end is subjected to a bluing treatment by which the high tension bolt having the resistance to delayed cracking of >=130kgf/mm.<2> tensile strength is obtd.