关键词: 低屈强比, 多相组织, Q500qE高强钢板, 60 mm厚板

Abstract: The continuous cooling transformation ( CCT) curve, microstructure and mechanical properties of Q500qE low yield ratio high strength steel 60 mm thickness plate have been studied by JMatpro software, scanning electron microscope and mechanical property tests. The results show that by control rolling and control cooling process: the final rolling temperature 800-840 °C , the into water temperature 660-680 X. and the final cooling temperature 400-450 °C, the microstnicture of steel is composed of ferrite , bainite and MA( martenite/austenite) island, and many large angle grain boundaries exist in junction of two phases and in bainite. The properties of the steel at 1/4 and 1/2 thickness are yield ratio 0.78-0.79, yield strength ≥500 MPa, tensile strength ≥640 MPa, charpy impact energy of 1/2 thickness at -40 °C ≥ 200 J, for HAZ charpy impact test at -40 °C, the charpy impact energy of HAZ ≥100 J.

Key words: Low Yield Ratio, Multi-Phases Microstructure, Q500qE High Strength Steel, 60 mm Thickness Plate