HIGH-STRENGTH STEEL SHEET PLATED WITH ZINC BY HOT DIPPING WITH EXCELLENT FORMABILITY AND PROCESS FOR PRODUCING THE SAME

摘要

A high-strength steel sheet plated with zinc by hot dipping which has excellent processability. It can be produced using a production line which includes zinc plating by hot dipping and in which a sufficient austempering time after annealing is not secured, without necessitating a special structural control as a pretreatment. The high-strength steel sheet plated with zinc by hot dipping contains 0.05-0.3 mass% carbon, up to 1.4 mass% (including 0 mass%) silicon, 0.08-3 mass% manganese, 0.003-0.1 mass% phosphorus, up to 0.07 mass% sulfur, 0.1-2.5 mass% aluminum, 0.1-0.5 mass% chromium, and up to 0.007 mass% nitrogen, provided that silicon + aluminum = 0.5 mass%, with the remainder consisting of iron and unavoidable impurities. The steel sheet has a volume content of residual austenite of 3% or higher, and residual austenite grains have an average aspect ratio of 2.5 or lower.