Method of producing hot-dip galvannealed steel sheet.

摘要

A method of producing a hot-dip galvannealed steel sheet from a very-low-carbon cold- rolled steel sheet containing not less than 0.01 wt% but not more than 0.1 wt% of Ti, by subjecting the cold rolled steel sheet to a process conducted in a continuous hot-dip galvanizing system including a heat treatment, hot-dip galvanizing and a subsequent galvannealing. The method is characterized by the steps of: subjecting the cold-rolled steel sheet to a degreasing and an acid cleaning; subjecting the degreased and acid-cleaned steel sheet to a heat treatment conducted in a reducing gas atmosphere; and cooling the heat-treated steel sheet at a temperature not lower than 380 DEG C but not higher than the hot-dip galvanizing bath temperature, before the steel sheet is subjected to the hot-dip galvanizing. The very-low-carbon cold- rolled steel sheet contains, besides not less than 0.01 wt% but not more than 0.1 wt% of Ti, not more than 0.005 wt% of C, not less than 0.01 wt% but not more than 0.1 wt% of A l , not less than 0.01 wt% but not more than 0.1 wt% of Ti, and the balance substantially incidental inclusions and Fe.