Method for manufacturing high-strength galvannealed steel sheet
AssigneeJfe Steel Corporation
InventorsYoichi MAKIMIZU, Yoshitsugu SUZUKI, Yasunobu NAGATAKI
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Abstract
There is provided a method for manufacturing a high-strength galvannealed steel sheet having excellent coating adhesiveness and corrosion resistance whose base material is a high-strength steel sheet containing Si and Mn. The method includes performing an oxidation treatment on a steel sheet including Si and Mn in a first zone having an atmosphere of an oxygen concentration, thereafter performing an oxidation treatment in a second zone having an atmosphere of an oxygen concentration, thereafter performing reduction annealing and galvanizing, and further performing an alloying treatment by heating the galvanized steel sheet.
Claims8
A method for manufacturing a high-strength galvannealed steel sheet, the method comprising:
- performing an oxidation treatment on a steel sheet including Si and Mn in a first zone having an atmosphere with an oxygen concentration in the range of less than 1 vol % under conditions that an average heating rate of the steel sheet is in the range of 20° C./sec or more and a maximum temperature T of the steel sheet is in the range of 400° C. to 500° C.
- thereafter performing an oxidation treatment on the steel sheet in a second zone having an atmosphere with an oxygen concentration in the range of 1 vol % or more under conditions that an average heating rate of the steel sheet is in the range of less than 10° C./sec and a maximum temperature T of the steel sheet is in the range of 600° C. or higher;
- thereafter reduction annealing and galvanizing the steel sheet;
- and
- further performing an alloying treatment on the steel sheet by heating the galvanized steel sheet at a temperature in the range of 460° C. to 600° C. for a duration in the range of 10 seconds to 60 seconds.
Dependencies are inferred from the claim text.