| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot-dip galvanized steel sheet having both yield strength and warm formability, which can be produced by short-lasting austempering by means of a CGL, and to provide a production method of the high strength hot-dip galvanized steel sheet.SOLUTION: The high strength hot-dip galvanized steel sheet has a component composition which contains by mass%, C:0.05 to 0.3%, Si:1 to 3%, Mn:1 to 3%, P:0.1% or less, S:0.01% or less, Ti:0.02 to 0.2%, Al:0.001 to 0.1%, N:0.002 to 0.03% and the balance comprising iron and inevitable impurities and which satisfies 10[C]+0.4[Si]+[Mn]≤4.5...expression (1) and 0.8Ac1+0.2Ac3...expression (2). The high strength hot-dip galvanized steel sheet has a structure containing, by area ratios to the whole structure, bainitic ferrite of 40 to 65%, martensite (M)+residual γ of 20% or more, the M of 15% or less, residual γ of 10% or more, and ferrite (α) of 20 to 40%. In the high strength hot-dip galvanized steel sheet, a C concentration of the residual γ is less than 0.9 mass%, an average particle diameter of subgrain in both recrystallized α and non-recrystallized α is 3 μm or less, the area ratio of α and worked α each having a particle diameter of 5 μm or more is 5% or less, the average particle diameter of a TiC particle in the α particle is 10 nm or less. |
