GALVANNEALED STEEL SHEET HAVING EXCELLENT APPEARANCE

摘要

PURPOSE: To obtain a galvannealed steel sheet which is not formed with stripe patterns and has excellent appearance by using a crystal grain structure steel in which the structure bands consisting of specific equi-axed crystal gains and stretched crystal grains exist in surface layers as a base metal for plating. CONSTITUTION: The equi-axed crystal grain structure bands and the mixed crystal grain structure bands consisting of the equi-axed crystal gains and the stretched crystal grains exist in the surface layers in a range from at least 50μm from the surface of the crystal grain structure steel. The difference in the average crystal grain size between the adjacent mixed crystal grain bands and the equi-axed crystal grain bands is specified to <=1.0 in ferrite grain size No. Such steel sheet is obtd. by adequately controlling various conditions, such as hot rolling conditions, cold rolling conditions and annealing conditions of continuous plating lines in a process for production of the conventional thin steel sheets. This steel sheet is subjected to coating of galvannealed layer as original plate.