Cold-rolled steel strip and hot-dip coated cold-rolled steel strip for use as building material and manufacturing method thereof

摘要

A cold-rolled steel strip or hot-dip coated cold-rolled steel strip for use as a fire-proof building member has composition consisting of 0.01-0.25 wt. % C, up to 1.5 wt. % Si, 0.05-2.5 wt. % Mn, up to 0.1 wt. % P, no more than 0.02 wt. % S, 0.005-0.1 wt. % Al, 0.05-1.0 wt. % Mo, optionally 0.005-0.2 wt. % one or more selected from Ti, Nb, V and W, optionally one or more of 0.05-0.6 wt. % Cu, 0.05-0.6 wt. % Ni, 0.05-3.0 wt. % Cr and 0.0003-0.003 wt. % B and the balance being essentially Fe except inevitable impurities. The cold-rolled steel strip is manufactured by hot-rolling, acid-pickling, cold-rolling and then annealing at a temperature above its recrystallization temperature but below 950° C. The hot-dip coated cold-rolled steel strip is manufactured in the same way but in-line heating a cold-rolled steel strip at a temperature above its recrystallization temperature but below 950° C. and then immersing it into a coating bath. The annealed or hot-dip coated steel strip may be further cold-rolled with such a slight duty to induce a plastic strain of 1-5%.