Patent ID: 6605166
Filing Date: 2003-08-12
Classification: C21D,C22C

Abstract:
A method for producing a high-strength bolt having excellent delayed fracture resistance and stress relaxation resistance, comprising:preparing a steel material comprising 0.50 to 1.0% by mass of C, 0.5% by mass or less of Si, not including 0% by mass, 0.2 to 1% by mass of Mn, 0.03% by mass or less of P, including 0% by mass; and 0.03% by mass or less of S, including 0% by mass; said steel material comprising a total of less than 20% by mass of a pro-eutectoid ferrite structure, a pro-eutectoid cementite structure, a bainite structure and a martensite structure; and a remainder of a pearlite structure; drawing said steel material severely to obtain a steel wire; forming said steel wire into a bolt shape through a cold heading, to obtain a shaped steel wire; and subjecting said shaped steel wire to a blueing treatment at a temperature within a range of 100 to 400Â° C.; thereby producing a high-strength bolt having excellent delayed fracture resistance and stress relaxation resistance in addition to a tensile strength of 1200 N/mm2 or higher.