Hot galvanized steel sheet and method for producing galvannealed steel sheet, hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet

摘要

PROBLEM TO BE SOLVED: To provide methods of manufacturing a galvanized steel plate and an alloyed galvanized steel plate that have excellent mechanical characteristics and plating characteristics by efficiently determining a maximum heating temperature in an oxidation treatment.SOLUTION: There are provided methods of manufacturing a galvanized steel plate and an alloyed galvanized steel plate that are characterized in that when the galvanized steel plate is manufactured through an oxidation treatment for heating a steel plate containing 0.1-3 mass% Si in an oxidative atmosphere to form iron oxide on a surface of the steel plate, a reduction treatment for heating the steel plate after the oxidation treatment in a non-oxidative atmosphere to reduce the iron oxide, and a plating treatment for galvanizing the steel plate after the reduction treatment, the methods include: grasping an iron oxide formation state of a steel plate surface layer in a heating process in the oxidative atmosphere for the steel plate and a contrast steel plate such that a proper maximum heating temperature Wa in the oxidation treatment is established; finding a temperature Xt at which the steel oxide of the steel plate has transition in form and a temperature Wt at which the iron oxide of the contract steel plate has transition in form on the basis of the iron oxide formation; and carrying out the oxidation treatment in which Xa found from those Xt, Wt, and Wa according to an expression (A) is defined as the maximum heating temperature. Here, Xa=Wa+Xt-Wt (A).