METHOD FOR MANUFACTURING HIGH-TENSILE STEEL FOR LASER BEAM WELDING OR LASER BEAM ARC HYBRID WELDING HAVING TENSILE STRENGTH OF =1,100 MPa

摘要

PPROBLEM TO BE SOLVED: To provide a method for manufacturing a high-tensile steel plate for ensuring excellent toughness of the steel plate and a joint, suppressing softening of a welded heat affected zone, and also ensuring the tensile strength of the joint of 1,100 MPa, in the super-high-tensile steel plate which is welded by the laser beam arc hybrid welding and whose main structure is martensite and which has tensile strength of 1,100 MPa. PSOLUTION: When manufacturing a steel plate by the reheat-hardening step and the thermo-mechanical treatment step by using a steel slab in which the carbon equivalent is set to be 0.45-1.2% in order to make component range of each element adequate, and in order to reliably make the transformation structure of the steel plate be a martensitic structure, and further, in order to suppress softening of a welded heat affected zone, the Nb equivalent related to the precipitation-reinforcing element is set to be 0.09-0.80%, tempering is carried out at the temperature of 550C and below the Ac1 transformation point in order to suppress softening of the welded heat affected zone. PCOPYRIGHT: (C)2011,JPO&INPIT