| 摘要 |
PROBLEM TO BE SOLVED: To improve the image clarity of a steel sheet after coating and the flaking resistance of plating coating by forming Al-contg. Fe-Zn alloy plating film having specified surface roughness on a dead-soft steel having a specified compsn. SOLUTION: The compsn. of a steel is, by weight, <=0.004% C, 0.03 to 0.13% Si, 0.05 to 0.4% Mn, 0.007 to 0.02% P, 0.018 to 0.05% Ti, 0 to 0.02% Nb, 0.005 to 0.1% Al, 0 to 0.005% B, and the balance Fe with inevitable impurities. On at least one side of a steel sheet produced from the steel having this compsn., Fe-Zn alloy plating film contg. 0.18 to 0.5% Al is formed. The surface roughness of this plating film is regulated to <=1μm by arithmetic average roughness (Ra), and the number of the peaks of troughs is regulated to 320 to 600/25.4mm. Furthermore, it is preferable that the steel sheet before the plating is retained in the temp. range of 600 to 500 deg.C for 20 to 60sec in a reducing atmosphere composed of hydrogen and nitrogen and in which the dew point is regulated to -20 to -40 deg.C.
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