Microstucture And Mechanical Properties Of Mocro-alloyed TWIP Steel

In recent years, automobile industry developing rapidly pull the demand for automotive materials. At the same time, thet trends of the development of auto industry are safety and energy conservation and emissions reduction. Beause of twinning induced plasticity effect or martensite phase transformation induced plasticity in the process of deformation, TWIP steels have the large elongation(95%) and high tensile strength(1100MPa). Although the elements of Nb、V and Ti have more influence on the microstructure and mechanical properities of TWIP steels, and the research of the mechanical properities of TWIP steel containing a variety of micro alloying elements is vary rare.Two kinds of TWIP steels with or without addition of Nb、V and Ti are introduced in this paper. And the effects of Nb、V and Ti on stacking fault energy(SFE) and mechanical properities were studied by means of tensile and compress tests. Some experimental apparatus(OM、XRD、SEM and TEM) were used to analyse the microstructure. And the mechanisms of TWIP effect and approaches of martensitic transformation were systematically investigated. The main contents are described as follows:(1)Calculated the stacking fault energy of the Fe-Mn-Al-Si-C alloy and analyzed the influences of the element Nb、V and Ti. Addition the element of Nb、V and Ti reprove the SFE of experient steel.(2)The deformation mechanisms and associated microstructure changes during tensile deformation of two kinds of TWIP steels were systematically investigated at room temperatureconditions. Compared with the steel without Nb、V and Ti, it is fould that the tensile strength and elongation of the steel with Nb、V and Ti decrease, but the yield strength increases, and the main deformation mechanism is TWIP effect; It is occurred TRIP effect during tensile deformation of the steel without Nb、V and Ti.(3)At room temperature conditions, dislocation gliding throughout the deformation process of the steel with Nb 、 V Ti during the static compression deformation. In the process of deformation, the stacking faults appear gradually as the severe dislocation reaction; As deformation continues, the reason of stacking faults becoming blurred is The emergence of the deformation twins, a good deal of stacking faults were replaced by a lot of deformation twins.Because twins take strenuous exercise, development of deformation twins is a process of aggradation and incision. At the end, the grain is divided small enough to exercise its restraints upon the generation of deformation twins, so weakened TWIP effect.