PURPOSE: To produce an alloyed an hot dipped hot rolled high tensile steel sheet having excellent tensile strength and workability by subjecting the surface of a steep strip having a specific compsn. to hot dip Zn coating then to a heat treatment under specific conditions thereby alloying a Zn-plated layer to a Zn-Fe alloy.
CONSTITUTION: The hot rolled steel strip made of the compsn. contg., by weight %, 0.015W0.30% C, 0.10W2.5% Mn, <0.015% S, 0.010W0.10% Al, 0.005W0.50% in total of 1 or ≥2 kinds among Nb, Ti and V and further contg. <0.20% P and <0.20% Si is continuously passed in a Zn hot dipping bath by which the steel strip is subjected to the Zn hot dipping treatment. The treated strip is heated to 550W850°C and is held at said temp. for 1sec to form the Zn-Fe alloy layer contg. 7W35% Fe by the cross-diffusion of the Zn of the plating layer and the Fe of the steel strip; thereafter the strip is cooled down to ≤500°C at an average cooling rate of ≥10°C/sec. The alloyed Zn hot dipped, hot rolled high tensile steel sheet for an automobile body having ≥45kgf/mm2 tensile strength and excellent workability is obtd.
KAWABE JUNJI
HASHIGUCHI KOICHI
OKANO SHINOBU
