Ultra-fine-grained high-hole-expansion hot-rolled pickled 420mpa grade low-alloy high-strength steel and preparation method thereof

Abstract

This invention relates to the field of steel material preparation technology, specifically to an ultrafine-grained, high-porosity, hot-rolled, pickled 420MPa grade low-alloy high-strength steel and its preparation method. The chemical composition contains elements such as C, Si, Mn, Nb, Ti, Cu, and Ni, and satisfies Ti / N = 3.0–5.0 and (Nb+Ti) / C = 0.40–0.70. The method includes hot metal pretreatment, converter smelting, LF+RH refining, continuous casting, slab heating (1140–1160℃), hot rolling, controlled cooling, coiling (580–620℃), leveling, and pickling. The microstructure of the steel plate consists of ultrafine ferrite and a small amount of pearlite. The ferrite grain size is 3.0 to 4.5 μm, the yield strength is 443 to 512 MPa, the tensile strength is 508 to 578 MPa, the elongation is 25.5% to 35.0%, and the porosity is 81% to 115%. It has both high strength and excellent flanging formability.

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