METHOD FOR PRODUCING ULTRA HIGH STRENGTH MEMBER AND USE OF ULTRA HIGH STRENGTH MEMBER

摘要

Disclosed are a method for manufacturing an ultra high strength member having a tensile strength (TS) of 1180 MPa or more, whereby an ultra high strength member excellent in delayed fracture resistance can be manufactured by a hot pressing process at low cost, and a method for using the same. A steel sheet is heated at first heating temperature (700 to 1000°C), formed into a shape of a member at the first heating temperature and simultaneously cooled, and after completion of the cooling, shear punched into a desired shape to obtain an ultra high strength member. The ultra high strength member is subjected to first heat treatment including heating and retaining the member held at second heating temperature (100 to less than 300°C) for 1 second to 60 minutes. The resulting ultra high strength member has a tensile strength of 1180 MPa or more.