| Based on the characteristics of thin slab casting and rolling process(TSCR), theweathering mechanism and micro-alloying technology of thin slab casting and rolling ultrahigh strength weathering (UHSW) steel were studied systematic. Also, the phasetransformation, austenite recrystallization law, phase transition law, Ti precipitates law of Timicroalloyed UHSW steel were investigated. These clarify the strengthening mechanism of Timicroalloyed UHSW steel. UHSW steel whose yield strength is700MPa Grade had beenused for next generation light weight container.Through investigating weathering mechanism of UHSW steel, Cu-Cr-Ni weatheringsystem was designed. Properties of Four kinds UHSW steel produced by micro-alloyingtechnology roadmap under high P conditions were compared analyzed. And found that thestrength of steel produced by various technologies routes all close to700MPa but display poorexperimental toughness. Through Composition Optimization of design, the content of Mn, Crwere increased, the content of P were lowered. The strength of steel reached700MPa,3~4μm Structure Refinement, while maintaining the weathering resistance of the steel,increasing steel low-temperature impact toughness and cold working capacity. Andcomprising alloy cost of three micro-alloying elements Nb, V, Ti, determined using a Ti microalloying production of UHSW steel technology roadmap.The microstructure evolution of Ti microalloyed UHWS steel was investigatedsystematically. The basic equiaxed uniform microstructure appears after the first rolling, theferrite phase microstructure is more uniform. The first rolling has played a key role duringmicrostructure evolution. The grain size decreases with the increase of rolling passes, thedifference of grain size between surface and center decrease. Microstructure becomes moreuniform in the thickness direction of the sheet.The austenite recrystallization law of the UHSW steel was indicated through the thermalsimulation experiment. And complete recrystallization appeared between each rack whosecontrolled rolling mode is F1-F4, partial recrystallization occurred after F4rack,non-recrystallization occurred after F5rack.The phase transformation of the UHSW steel was indicated through the thermalsimulation experiment. The phase transition point decreases with increasing cooling rate. Withthe increase of continuous cooling rate, the microstructure of UHSW steel gradually from thehigh temperature transformation phase in which ferrite is the main feature organizationchange to low-temperature transformation phase in which granular bainite and lath bainite are the main feature. Microhardness of UHWS steel first increased and then decreased, andfinally increased with the decreasing coiling temperature.The precipitation rule of Ti precipitates in UHSW steel was investigated. Thestrengthening mechanism of Ti micro alloyed UHSW steel was clarified. Fine grainstrengthening is the most important strengthening method, strength is more than300MPa.Strength from precipitation strengthening and dislocation strengthening effects are more than150MPa. Strength from solid solution strengthening effect is approximately100MPa.Through investigating the technology of smelting, continuous casting, hot rolling of Timicro alloyed UHSW steel, the700MPa grade Ti micro alloyed UHSW steel was successfullydeveloped. Steel possess good performance, such as good low temperature toughness,ductile-brittle transition temperature below-60℃and good weld ability. The weight loss rateof UHSW steel is1.554g/m~2.h~1.874g/m~2.h. Its weathering performance is similar withordinary container board. When it used for lightweight container, the container possess goodprocessing properties and weld ability. The containers passed11test classificationrequirements. It plays an important role for losing weight and reducing costs in logistics andtransport industry.
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