Method for manufacturing a galvanized steel sheet

摘要

A galvanized steel sheet includes a zinc plating layer which is disposed on a steel sheet containing 0.01% to 0.15% C, 0.001% to 2.0% Si, 0.1% to 3.0% Mn, 0.001% to 1.0% Al, 0.005% to 0.060% P, and 0.01% or less S on a mass basis, the remainder being Fe and unavoidable impurities, and which has a mass per unit area 20 g/m2 to 120 g/m2. An oxide of at least one selected from the group consisting of Fe, Si, Mn, Al, and P is present in a surface portion of the steel sheet that lies directly under the zinc plating layer and that extends up to 100 μm from the surface of a base steel sheet. The amount of the oxide per unit area is 0.05 g/m2 or less in total. The steel sheet has excellent corrosion resistance, anti-powdering property during heavy machining, and strength.

主权项

1. A method for manufacturing a galvanized steel sheet, comprising:
annealing and galvanizing a steel sheet in a continuous galvanizing line, wherein the steel sheet is galvanized such that the partial pressure (Po2) of oxygen in the atmosphere of an all-radiant tube annealing furnace satisfies the following inequality at a temperature of 500° C. to 900° C.:
Log Po2≦−14−0.7×[Si]−0.3×[Mn]  (1)where [Si] represents a content in mass percent of Si in steel, [Mn] represents a content in mass percent of Mn in steel, and Po2 represents a partial pressure (Pa) of oxygen,
wherein the steel sheet contains a zinc plating layer, and an oxide of at least one selected from the group consisting of Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, and Ni is present in a surface portion of the steel sheet that lies directly under the zinc plating layer and that extends up to 100 μm from the surface of a base steel sheet, the content of Si is from 0.001% to 0.2% by mass, and an amount of oxide per unit area is 0.05 g/m2 or less.