Study On Rolling Processes And Application Performance Of540/590MPa Wheel Steel

In recent years, the quantity of world auto mobiles have been increasing with time, meanwhile the problems like power resource shortage and environment contamination have been put in focus. Energy conservation has become a serious problem, as a solution high strength steel wheel has a widely application. In this research, use TMCP technology with addiction Nb-Ti micro alloy to improve high strength wheel steel, as results the high performance of welding property has been maintained. The property of hole expansion and welding are both important evaluation standards for steel wheel, therefore in order to get best micro observation and tech data, hole expansion and welding tests have been taken on different steel specimen.(1) Steel specimen composition determination, first did the hot rolling test on Φ450rolling machine, then observed and analysis the micro structure, as results there are mainly ferrite structure with lower carbon content.(2) Steel mechanical property tests which include tension test, hole expansion test, bending test and impact test all indicate the well quality. When the coiling temperature is low, dislocation strengthening play the main role, when the coiling temperature is high precipitation strengthening will be enhanced.(3) Through hole expansion test on different composition and process specimen, found relationship between different micro structures and wheel steel hole expansion property. As a result, the specimen with ferrite and pearlite microstructure has best hole expansion property, the specimen with ferrite and martensite microstructure has worst property. The steel with ferrite and bainit microstructure has a better property on hole expansion tests. In addition, ferrite with granular bainit exceed ferrite with strip banite on hole expansion property.(4) The test steel all work well on flash welding, the appearance on weld joint are nice. The mechanical performance tests showed good tension property, the force basically has no difference from the substrate, under certain circumstances the thermal process region has a stable elongation, most fractures are on substrate. (5) Observed the microstructure of fracture on SEM showed that beside the substrate region the fracture mechanism on thermal process region is all ductile fracture.(6) The Micro-structure observation shows the welding parts and thermal process parts are both bainite, among the welding line M-A islands are relatively coarse and big, thermal parts are basically bainite, fine grain parts are equiaxed ferrite. The favorable welding thermal process region has a well distributed hardness, also on welding line, coarse grain and fine grain region there is small deviation on hardness.(7) The orthogonal analysis shows the flash current has little affect on welding, the best process parameters varied from the component and thickness.