| 摘要 |
PURPOSE:To obtain a continuously hot dip galvanized mild steel sheet having no surface defects by properly controlling the structure of a hot rolled steel sheet, the draft of cold rolling and the temp. during recrystallization annealing and by providing an unrecrystallized structure to the surface layers of a mild steel sheet and a recrystallized structure to the central layer by recrystallization annealing. CONSTITUTION:A steel ingot contg., by weight, <0.08% C, <0.05% Si, <0.4% Mn, <0.05% P and <0.1% Al is hot rolled to form a hot rolled steel sheet consisting of coarse-grained surface layers and a fine-grained central layer. The steel sheet is cold rolled at 30-75% draft and subjected to recrystallization annealing at <=700 deg.C to provide an unrecrystallized structure to the surface layers of the mild steel sheet and a recrystallized structure to the central layer.
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