DESIGN OF HIGH MANGANESE STEELS: CALCULATION OF SFE AND Ms TEMPERATURE

摘要

High Mn steels have great plasticity when deformed due to twinning, known as TWIP effect (Twinning Induced Plasticity) or due to martensitic transformation, called as TRIP effect (Transformation Induced Plasticity). The stacking fault energy (SFE) controls the deformation mechanism. So calculation of SFE value and Ms temperature is essential for designing of high manganese steels. For twinning to occur, it is usually necessary for the steel stacking fault energy (SFE) to be in the range of 18-35 mJ/m~2. If the SFE is <18 mJ/m~2, twinning is replaced by martensitic transformation. However, if it is >35 mJ/m~2, then the slipping processing will be the only mechanism that contributes to the plastic deformation of steel. For alloys with Mn content between 15% and 25% the SFE is intermediate and then TRIP and TWIP effects coexist. In this work stacking fault energy of some compositions of High manganese steel has been calculated through thermodynamic model and X-ray line profile analysis and these values are verified with the SFE values available in literature. It was found that value of stacking fault energy calculated through thermodynamic model is found to be close with the value calculated through TEM node method and have large difference in values with comparison to X - ray diffraction method. Different empirical equations are used to calculate the Stacking fault energy of high manganese compositions and Martensite start temperature (Ms). Empirical equations are found to be more suitable for SFE calculation for austenitic stainless steels. Ms Temperature calculation from empirical equations is found to be more suitable for austenitic and high manganese steels.