MANUFACTURE OF HOT DIP GALVANNEALED STEEL SHEET HAVING EXCELLENT STRETCH-FLANGING PROPERTY USING HIGH STRENGTH HOT-ROLLED ORIGINAL SHEET

摘要

PURPOSE: To stably manufacture a high strength galvannealed steel sheet having excellent workability, particularly, stretch-flanging property. ;CONSTITUTION: In a continuous hot dip galvannealing line, in which the steel containing 0.001-0.30% C, ≤2.00% Si, 0.2-2.0% Mn, ≤0.10% P, ≤0.01% S, 0.005-0.10% Al and 0.01-0.20% Nb and the balance Fe with the inevitable impurities is hot-rolled and wound at 600-250°C to make the hot-rolled steel sheet and cold-rolling is unnecessary after pickling, the high strength galvannealed steel sheet is manufactured by heating and cooling so as to satisfy the following conditions to the max. soaking temp. T (°C) and cooling speed CR after alloying heating according to the steel component factor (K) (K=C +(1/5)(Mn+Si)+(1/4)Cr), i.e., in the case of k0.34%, T≤800°C, and in the case of K≥0.34, T≤800°C and 282.5×[logCR]+T≤1100°C.;COPYRIGHT: (C)1993,JPO&Japio