HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET AND HIGH-STRENGTH ALLOYED HOT-DIP GALVANIZED STEEL SHEET EXCELLENT IN MECHANICAL CUTTING PROPERTY,AND MANUFACTURING METHOD THEREOF

摘要

There is provided a high-strength hot-dip galvanized steel sheet and the like excellent in mechanical cutting property, which are capable of obtaining high ductility while ensuring high strength with maximum tensile strength of 900 MPa or more. The high-strength hot-dip galvanized steel sheet has a sheet thickness of 0.6 to 5.0 mm and has a plating layer on a surface of a steel sheet with component compositions being set in appropriate ranges, in which the steel sheet structure contains a 40 to 90% ferrite phase and a 3% or more retained austenite phase by volume fraction. In the retained austenite phase, a solid solution carbon amount is 0.70 to 1.00%, an average grain diameter is 2.0 µ m or less, an average distance between grains is 0.1 to 5.0 µ m, a thickness of a decarburized layer in a steel sheet surface layer portion is 0.01 to 10.0 µ m, an average grain diameter of oxides contained in the steel sheet surface layer portion is 30 to 120 nm and an average density thereof is 1.0 X 10 12 oxides/m 2 or more, and moreover, a work hardening coefficient (n value) during a 3 to 7% plastic deformation is 0.080 or more on average.