| 摘要 |
Disclosed is a galvanized steel sheet which has a tensile strength of not less than 80 kgf/mm2 and a yield ratio of not more than 60%, and which is applicable to members of an automobile body, particularly those requiring strength. By appropriately controlling the amounts of C within the range of 0.08-0.20 wt%, Mn within the range of 1.5-3.5 wt%, Al within the range of 0.01-0.1 wt%, P 0.01 wt% or less, S 0.01 wt% or less, and one or both of Ti and Nb within the range of 0.01-0.1 wt%, the structure of the steel sheet is formed into a dual-phase structure having a second phase structure. The steel sheet is recrystallization-annealed, galvanized while it is maintained at a temperature range near 500.degree.C, and then is cooled. By controlling the rate of cooling the steel sheet, the second phase structure generated is prevented from hardening more than necessary. The galvanized high-strength steel sheet has a low yield ratio and excellent stretch-flanging properties. |
