Research Of Trip780 Manufacture Organization And Performance

TRIP (Transfornation Induced Plasticity) steel which is developed to meet the auto industry is a kind of low carbon, low alloy and high strength steel plate. Its properties are high intensity and high ductility. The microstructure of TRIP steel is ferrite, bainite and retained austenite. TRIP effect is that retained austenite occures martensite deformation to achieve the purpose of high strength and high toughness. TRIP steel has the obvious superiority. It can reduce the weight of the car, reduce fuel consumption, resist the plastic deformation of collision which significantly improve the car level of securityIn this study, microstructure is acquired by different thermal simulation experiments for four tested steels. The microstructure of different process is analyzed by optical microscope, scanning electron microscope and transmission electron microscope. The volume fraction of retained austenite can be measured by using the X-ray diffraction method. The mechanical properties of tested steel after thermal simulation experiments can be achieved by tensile test. The relation of microstructure and mechanical properties is discussed. The appropriate ingredient and the better heat treatment technics for cold rolled TRIP780steel in Benxi Iron&Steel Group can be found. Some conclusions can be acheived through the research of organization and performance for TRIP780.1) The heat treatment process has effect on organization and performance. In general, the running speed of the steel strip has little influence on organization and performance. With the rise of the annealing temperature, the ferrite content reduces, bainite content increases gradually, the large shape ferrite turns into small piece of ferrite, the volume fraction of retained austenite and the carbon content increase after reducing to a low edd, and regular changes of tensile strength, yield strength and yield ratio appear insignificant. Along with the rise of bainite isothermal temperature, the grain of bainite is thick gradually, the volume fraction of retained austenite and the carbon content first increased and then decreased and tensile strength, yield strength and yield ratio is on a declining curve. When the running speed of the steel plate is120m/min and thermal simulation technology is820℃×110s+410℃×440s, comprehensive performance of TRIP780steel is the best.2) Niobium and titanium are important alloy element for TRIP steel. Niobium can make the grain refined which can not only improve the strength of the steel plate but also improve the toughness of the steel plate. The solid solution of niobium can improve retained austenite content of TRIP780. Nb precipitates can improve the nucleation rate of ferrite and increase the percentage volume of ferrite. The compounds containing titanium and niobium have deposition strengthening effect and the steel containing titanium produced the role of deposition strengthening is more notable. The carbide containing titanium affect diffusion velocity of carbon, further influence austenite morphology.3) After820℃×110s+410℃×440s thermal simulation technology,1#steel has best mechanical properties in the four tested steels. Its tensile strength is830Mpa, yield ratio is0.6and retained austenite content is the highest. Therefore, the TRIP780steel’appropriate ingredient is1#steel.