| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength hot dip galvanized steel sheet with a hyperfine-grained structure, which has excellent mechanical properties, particularly in ductility. SOLUTION: The steel sheet has a composition in which C, Si, Mn, Ni, Ti and Nb are particularly contained in ranges respectively satisfying the following inequalities (1), (2) and (3) in the steel components, and the balance Fe with inevitable impurities, and also has a steel structure in which the volume fraction of ferrite is≥70 vol%, the volume fraction of retained austenite is≥5 vol%, and also, the average crystal grain size of ferrite is≤3.5μm: 637.5+4930äTi*+(48/93)×[%Nb]}≥A<SB>1</SB>(1), A<SB>3</SB>≤860 (2), and [%Mn]+[%Ni]≥1.3 (3); wherein, Ti*=[%Ti]-(48/32)×[%S]-(48/14)×[%N], A<SB>1</SB>: the predicted value (°C) of an A<SB>1</SB>transformation point obtained by the calculation inequality, and A<SB>3</SB>: the predicted value (°C) of an A<SB>3</SB>transformation point obtained by the calculation inequality. COPYRIGHT: (C)2004,JPO&NCIPI
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