| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high strength hot dip Zn-Al-Mg alloy plated steel sheet in which pearlitic transformation in hot dip plating is suppressed, and which has a low yield ratio and excellent strength and corrosion resistance. SOLUTION: A hot rolled steel strip produced by subjecting a slab comprising 0.05 to 0.20% C,≤1.5% Si, 1.0 to 2.5% Mn,≤0.05% P and≤0.01% S to hot rolling or a cold rolled steel strip produced by subjecting the same to pickling and cold rolling successively to the hot rolling is used as a plating original sheet. The plating original sheet is heated to the temperature range of Ac<SB>1</SB>to Ac<SB>3</SB>in a reduction annealing furnace, and thereafter cooled to 650°C at a cooling rate of 3 to 10°C/s, further cooled to 440°C at a cooling rate of≥10°C/s, and then introduced into a hot dip Zn-Al-Mg alloy plating bath heated to a bath temperature of≤440°C, and taken up so as to temper into a composite structure of ferrite with a mean crystal grain size of≤15μm and martensite with a volume ratio of 5 to 45%. Thus, the high strength hot dip Zn-Al-Mg alloy plated steel sheet having a low yield ratio can be produced. COPYRIGHT: (C)2006,JPO&NCIPI
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