METHOD FOR MANUFACTURING THE ULTRA HIGH STRENGTH STEEL PARTS WITH EXCELLENT CORROSION RESISTANCE

摘要

A method for manufacturing the ultra high steel part with excellent corrosion resistance is provided to manufacture the ultra high steel having the tensile strength more than 140kg/mm^2 after molding the steel sheet having the tensile strength less than 100kg/mm^2. A method for manufacturing the ultra high steel part with excellent corrosion resistance includes following steps: a step for manufacturing the cold rolling substrate iron having the tensile strength less than 100kg/mm^2 and 30~80% reduction rate((the thickness of the board before rolling / the thickness of the board after rolling) / the thickness of the board before rolling Î 100) using hot rolled steel sheet including carbon(C) 0.1~0.4wt%, nitrogen(N) less than 0.1wt%, aluminium(Al) less than 0.01wt%, phosphorus(P) less than 0.05wt%, manganese(Mn) 0.8~2wt%, boron 0.002~0.01wt%, and adding molybdenum(Mo) or chrome(Cr) 0.1~0.5wt and controlling B/N atomic ratio over 1; a step(S110) for manufacturing the plated steel sheet it forms the Al-Si-Bi system in the surface of the substrate iron or the Al-Si-Bi-Mg system plating layer; a step(S120) that the temperature of the plated steel sheet heats so that it become 850‹C or 1000‹C; and a step(S130) for molding to the form desiring the heated plated steel sheet in the mold and rapidly freezes at the same time is included.