Study Of Microstructure And Mechanical Properties Of Low Aluminium And Low Silicon TWIP Steel

Recently, in order to meet the automobile security, energy saving,weight loss, and environment protection, the iron and steel industry continue to innovate and upgrade in the development of high strength, high plasticity steels. TWIP steels containing high manganese have wide application prospects in the car industry owing to their properties of extremely high elongation and medium tensile strength. The traditional TWIP steels contain a relatively high level of aluminium and silicon (2-3mass%)content,which have a disadvantage on industrial production. Therefore, it is necessary to develop low aluminum, low silicon TWIP steels.Aluminium and silicon content of the designed TWIP steel in this subject are controlled in1mass%. Mechanical properties were studied by means of tensile tests and microstructures were characterized through an optical microscope (OM), a X-ray diffraction (XRD), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Furthermore, the effects of solution treatment and tensile speed on mechanical properties of the steels were analyzed. The main contents are described as follows:(1) The experimental steels were hot rolled, subsequently, solution treated under different temperature and time. The microstructures and mechanical properties of the experimental steels at different states were investigated by means of the uniaxial tensile test. The results indicate that the solution treatment leads to an increase in the comprehensive mechanical properties effectively. The specimens were deformed to different strains in tensile testing in order to investigate the deformation mechanisms of the steels.(2) The results of XRD analysis show that the hot rolled steel and the steels with solution treatment at the temperature of900℃.1000℃and1100℃for1h are fully austenitic both before and after tensile testing.(3) The cold rolled experimental steels were tensioned at low speed and high speed respectively. The effects of tensile speed on the microstructures, mechanical properties and plastic deformation mechanism were studied. The results indicate that at low tensile speed, the elongation declines with the tensile speed and the tensile strength does not change much; nevertheless, at a high tensile speed, the tensile strength increases gradually with the tensile speed, and the elongation reaches its peak and then drops sharply.(4) The fracture surface of the experimental steels was analyzed by SEM.The results show that the experimental steels have dimple fracture feature and exhibit good ductility. The process of deformation and fracture of the experimental steels is identified with the process of micro-hole nucleation, growth and coalescence.