high strength hot dip galvanized steel sheet excellent in impact resistance property and method for its production, and high strength hot dip galvanized steel sheet and method for its production

摘要

abstract a base steel sheet has a hot dip dip galvanized layer formed on a surface thereof, in which, in a steel sheet structure in a range of 1/8 thickness to 3/8 thickness centered around 1/4 thickness of a sheet thickness from a surface, a volume fraction of a retained austenite phase is 5% or less, and a total volume fraction of a bainite phase, a bainitic ferrite phase, a fresh martensite phase and a tempered martensite phase is 40% or more, an average effective crystal grain diameter is 5.0 µm or less, a maximum effective crystal grain diameter is 20 µm or less, and a decarburized layer with a thickness of 0.01 µm to 10.0 µm is formed on a surface layer portion, in which a density of oxides dispersed in the decarburized layer is 1.0 × 1012 to 1.0 × 1016 oxides / m2, and an average grain diameter of the oxides is 500 nm or less. _______________________ translation of the summary abstract patent: "High strength hot dip galvanized steel sheet excellent in impact resistance property and method for its production, and high alloy hot dip galvanized steel sheet" resistance and method for its production ". A base steel sheet has a hot dip galvanized layer formed on its surface, in which, in a steel sheet structure in a range of 1/8 of thickness to 3/8 of thickness centered around 1/4 of the thickness of the steel sheet from the surface. the volume fraction of the retained austenite phase is 5% or less, and the total volume fraction of a bainite phase, a bainitic ferrite phase, a new martensite phase, and a tempered martensite phase is 40% or more. , the effective crystal grain diameter is 5.0 µm or less, the maximum effective crystal grain diameter is 20 µm or less, and a decbureted layer with a thickness of 0.01 µm to 10.0 µm is formed in a portion of the surface layer in which the density of the oxides dispersed in the decarburized layer is 1.0 × 1012 to 1.0 × 1016 oxides / m2, and the average grain diameter of the oxides is 500 nm or less. .