Twinning Induced Plasticity Steels...

Twinning Induced Plasticity Steels  Twinning induced plasticity steels, also known as TWIP steel, are a class of austenitic steels which can deform by both glide of individual dislocations and mechanical twinning. The steels are fully austenitic and nonmagnetic, with no phase transformation. These steels represent one of the types of new families of high strength steels which have been developed in recent years to meet the increased demands of weight reduction in automobiles. The formation of deformation twins causes a large degree of deformation. This deformation mode is the reason behind the naming of this group of steels. First steel based on plasticity induced by mechanical twinning was found in 1998 which had strength of 800 MPa with a total elongation of above 85 %. These values varied with deformation temperature, strain rate and chemical composition. Composition and micro structure  TWIP steels contain a high level of manganese (Mn) content. These steels are normally composed of iron (Fe), 15 % to 30 % manganese (Mn), 1 % to 3 % silicon (Si) and 1 % to 3 % aluminum (Al). The steels usually contain large concentrations of Mn because it is crucial to preserve the austenitic structure based on the ternary system of Fe-Mn-Al. The main influence of Mn in TWIP steels is to control the stacking fault energy (SFE) and therefore the deformation mode. The addition of aluminum to Fe-high Mn TWIP steels is because it increases SFE significantly and therefore stabilizes the austenite against phase transformations which can occurs in the Fe-Mn steels during deformation. Furthermore, it strengthens the austenitic micro structure by solid solution hardening. Al also improves corrosion resistance. Silicon sustains the austenite transformation into martensite, since its lowers the SFE and increases the number of stacking faults that are nucleation sites for martensite. It also...