Patent ID: 9028626
Filing Date: 2015-05-12
Classification: C21D,C22C,C23C,Y10T

Abstract:
1. A method of manufacturing a high-strength galvanized steel sheet comprising: hot-rolling a slab comprising on the basis of mass percent, C: 0.05% to 0.3%, Si: 0.01% to 2.5%, Mn: 0.5% to 3.5%, P: 0.003% to 0.100% or less, S: 0.02% or less, and Al: 0.010% to 1.5%, the total of Si and Al being 0.5% to 2.5%, the remainder being iron and incidental impurities, to form a steel sheet; during continuous annealing, heating the steel sheet to a temperature of 750° C. to 900° C. at an average heating rate of at least 10° C./s at a temperature of 500° C. to an A holding that temperature for at least 10 seconds; cooling the steel sheet from 750° C. to a temperature of (Ms point—100° C.) to (Ms point—200° C.) at an average cooling rate of at least 10° C./s; reheating the steel sheet to a temperature of 350° C. to 600° C.; holding that temperature for 10 to 600 seconds to form a microstructure in the steel sheet that includes 20% or more of ferrite phase, 10% or less of martensite phase, and 10% to 60% of tempered martensite phase, on the basis of area percent, and 3% to 10% of retained austenite phase on the basis of volume percent, and the retained austenite phase has an average grain size of 2.0 μm or less; and galvanizing the steel sheet.