HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET, HIGH-STRENGTH ALLOYED HOT-DIP GALVANIZED STEEL SHEET EXCELLENT IN BAKE HARDENABILITY, AND MANUFACTURING METHOD THEREOF

摘要

Steel contains each of C, Si, Mn, P, S, Al, N, O, at a range from ⅛ thickness centered around a ¼ sheet thickness from a surface to ⅜ thickness centered around the ¼ sheet thickness from the surface at a base steel sheet, a structure of the base steel sheet contains, in volume fraction, 3% or more of a retained austenite phase, 50% or less of a ferrite phase, and 40% or more of a hard phase, average dislocation density is 5×1013/m2 or more, solid-solution C amount contained in the retained austenite phase is in mass % 0.70 to 1.00%, X-ray random intensity ratio of FCC iron in an texture of the retained austenite phase is 3.0 or less, ratio between a grain diameter relative to a rolling direction and a grain diameter relative to a sheet width direction of the retained austenite phase is 0.75 to 1.33.

主权项

1. A high-strength hot-dip galvanized steel sheet excellent in bake hardenability, comprising:
a base steel sheet containing, in mass %,
C: 0.075 to 0.400%,Si: 0.01 to 2.00%,Mn: 0.80 to 3.50%,P: 0.0001 to 0.100%,S: 0.0001 to 0.0100%,Al: 0.001 to 2.00%,N: 0.0001 to 0.0100%,O: 0.0001 to 0.0100% each,with the balance made up of Fe and inevitable impurities,wherein a structure of the base steel sheet contains, in volume fraction, 3% or more of a retained austenite phase, 50% or less of a ferrite phase, and 40% or more of a hard phase,at a range from ⅛ thickness centered around a ¼ sheet thickness from a surface to ⅜ thickness centered around the ¼ sheet thickness from the surface at the base steel sheet,an average dislocation density is 5×1013/m2 or more, a solid-solution C amount contained in the retained austenite phase is in mass % 0.70 to 1.00%,an X-ray random intensity ratio of FCC iron in a texture of the retained austenite phase is 3.0 or less,a ratio between a grain diameter relative to a rolling direction and a grain diameter relative to a sheet width direction of the retained austenite phase is 0.75 to 1.33,further, a hot-dip galvanized layer is formed at the surface of the base steel sheet and the sheet thickness becomes 0.6 to 5.0 mm.