High-strength galvanized steel sheet and method for manufacturing the same
AssigneeJfe Steel Corporation
InventorsYusuke Fushiwaki, Yoshiharu Sugimoto, Masahiro Yoshida, Yoshitsugu Suzuki
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Abstract
Provided is a method for manufacturing a high-strength galvanized steel sheet, made from a steel sheet containing Si and/or Mn, having excellent exfoliation resistance during heavy machining. When a steel sheet containing 0.01% to 0.18% C, 0.02% to 2.0% Si, 1.0% 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, is annealed and galvanized in a continuous galvanizing line, a temperature region with a furnace temperature of A° C. to B° C. (600≦A≦780 and 800≦B≦900) is performed at an atmosphere dew-point temperature of −5° C. or higher in a heating process.
Claims4
A method for manufacturing a high-strength galvanized steel sheet including a zinc plating layer, having a mass per unit area of 20 g/m2 to 120 g/m2, disposed on a steel sheet containing 0.01% to 0.18% C, 0.02% to 2.0% Si, 1.0% 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, the method comprising:
- annealing and galvanizing the steel sheet in a continuous galvanizing line equipped with an all-radiant tube-type furnace, wherein the steel sheet is not oxidized prior to annealing, and
- setting the temperature of the all-radiant tube-type furnace such that the furnace temperature reaches a temperature region of A° C. and a temperature region of B° C. during the annealing and galvanizing process,
- wherein the annealing and galvanizing is performed at an atmosphere dew-point temperature of −5° C. or higher when the furnace temperature is in the regions of A° C. and B° C., and
- wherein the atmosphere dew-point temperature is −50° C. to −10° C. when the furnace temperature is outside the regions of A° C. and B° C.,
- where 600≦A≦780 and 800≦B≦900.
Dependencies are inferred from the claim text.