HIGH STRENGTH BOLT EXCELLENT IN DELAYED FRACTURE RESISTANCE

摘要

PROBLEM TO BE SOLVED: To provide a high strength bolt excellent in delayed fracture resistance which has a tensile strength of over 1200 N/mm2. SOLUTION: This bolt which is composed of a steel including C: 0.5-1.0% restrains the structure generation of one kind or more than one kind of pro- eutectoid ferrite, pro-eutectoid cementite, bentonite and martensite. The area rate of pearlite structure with particle No.7 or above in pearlite nodule size is made to be 80% or above. Then, the high strength wire material which is made to have a tensile strength of over 1200 N/mm2 and excellent delayed fracture resistance by strong extension work is used. The material is cut to a fixed length and both end parts are threaded by thread rolling or cutting.