HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET HAVING EXCELLENT FATIGUE CHARACTERISTICS AND MANUFACTURING METHOD THEREFOR

摘要

Provided are: a high-strength hot-dip galvanized steel sheet that has a tensile strength of at least 590 MPa and excellent fatigue characteristics with respect to hole punching; and a manufacturing method therefor. The structure of said steel sheet comprises a ferrite phase, with a mean grain diameter of 15 µm or less and an area ratio of at least 60%, and a martensite phase, with an area ratio of 5-40%. For each surface of the steel sheet, the total mass of one or more oxides selected from among iron, silicon, manganese, aluminum, phosphorus, niobium, and titanium oxides generated in a surface layer from the surface of the base steel directly beneath a galvanization layer to a depth of 100 µm into the steel sheet is less than 0.060 g/m². When manufacturing said steel sheet, during a continuous hot-dip galvanization process, soaking is performed at a temperature of 700-900°C, with the dew point of the surrounding atmosphere brought to -40°C or less for the temperature range of 700°C and up.