| 摘要 |
PURPOSE:To produce a galvannealed steel sheet free from white-striped surface defect by subjecting a cold rolled sheet of a Ti-containing dead-soft carbon steel to degreasing, to pickling, and to heating, immersing this steel sheet into a specific Al- containing hot-dip galvanizing bath at specific temp., and then carrying out alloying. CONSTITUTION:A cold rolled sheet of a dead-soft carbon steel which has a composition containing, by weight, 0.01-0.1% Ti, preferably containing <=0.005% C and 0.01-0.1% Al, and further containing, if necessary, 0.001-0.05% Nb, 0.0002-0.003% B, 0.02-0.1% P, etc., is degreased and subjected to pickling of >=0.2g/m<2> pickling loss. Subsequently, the above steel sheet is heated in a reducing gas atmosphere to undergo reduction annealing. This steel sheet is immersed into a hot dip galvanizing bath to undergo hot-dip galvanizing. At this time, the temp. of the steel sheet introduced into the plating bath is regulated to a temp. between 380 deg.C and the bath temp. Further, it is preferable that the plating bath contains 0.12-0.20% Al. Subsequently to the above plating, the plated steel sheet is heated and alloyed. At this time, it is preferable to regulate the amount of Fe diffused into the plating layer to 7-12%. By this method, the galvannealed steel sheet in which white-striped surface defect is effectively prevented can be obtained. |
