METHOD OF PRODUCING HOT-PRESSED STEEL

摘要

PROBLEM TO BE SOLVED: To provide a means of producing heat-treated steel suppressing the occurrence of scale of steel due to a heat treatment and having excellent weldability and coating adhesion. SOLUTION: The method of producing hot-pressed steel comprises a contact step and a hot press step. The contact step comprises a contact step of bringing a surface treatment liquid containing an inorganic binder and a metal pigment in a medium into contact with a base material thereby forming a liquid layer comprising the surface treatment liquid on the surface of the base material and a drying step of drying the base material on the surface of which the liquid layer comprising the surface treatment liquid is formed through the contact step thereby forming a protective film on the surface of the base material, thus obtaining steel for heat treatment. The hot press step comprises a heating step of heating steel for hot press to a temperature equal to or above Ac3point and keeping the state for a prescribed time, a cooling step of cooling and hardening the steel for which heating treatment for the prescribed time is finished, and a press step of carrying out shaping work of the steel by pressing the steel having deformation resistance lowered by the heating in the heating step. The metal pigment contained in the surface treatment liquid contains 5-20 mass% zinc oxide powder, 10-25 mass% bronze foil or the like and no high temperature oxidation resistant metal powder per total of the metal pigment and the solid portion of the inorganic binder. COPYRIGHT: (C)2011,JPO&INPIT