HIGH-STRENGTH, HOT-DIP-ZINC-COATED STEEL SHEET EXHIBITING EXCELLENT YIELD STRENGTH AND WARM FORMABILITY, AND METHOD FOR PRODUCING SAME

摘要

This high-strength, hot-dip-zinc-coated steel sheet is obtained by forming a zinc-coating layer on a steel sheet which has a characteristic composition containing, in terms of surface-area ratio to total composition, bainitic ferrite in the amount of 40-65%, martensite (M) + a remainder (γ) in the amount of 20% or more, M in the amount of 15% or less, the remainder (γ) in the amount of 10% or more, and ferrite (α) in the amount of 20-40%, wherein a remainder (γ) C-concentration is less than 0.9 mass%, and in terms of α, the average diameter of the recrystallized α and the subgrains in the un-recrystallized α particles is 3μm or less, the α having a particle diameter of 5μm or more and the treated-α surface area ratio are both 5% or less, and the average particle diameter of the TiC particles in the α particles is 10nm or less.