Patent ID: 7981463

Claim:
A method for manufacturing a hot-dip Sn—Zn coated steel sheet, comprising: pre-coating a Fe—Ni alloy containing between about 10 to 80 mass % of Ni, and a remainder being Fe on a steel sheet; immersing the steel sheet into a Sn—Zn hot-dip coating bath so as to form a hot-dip coating layer on the steel sheet; cooling the hot-dip coating layer at a cooling rate of about 10° C./sec to about 30° C./sec so as to obtain a hot-dip Sn—Zn coated steel sheet; measuring a differential scanning calorimetric curve of the hot-dip Sn—Zn coated steel sheet by a differential scanning calorimetry; and distinguishing whether the hot-dip Sn—Zn coated steel sheet has an objective microstructure by the measured differential scanning calorimetric curve, wherein the objective microstructure satisfies the following formula: (endothermic value of melting heat generated by Sn primary crystals)/{(endothermic value of melting heat generated by Sn primary crystals)+(endothermic value of melting heat generated by Sn—Zn eutectic crystals)}≧0.3.