The Effect of Deformation Temperature on the Deformation Mechanism of a Medium-Mn Advanced High-Strength Steel (AHSS)

The deformation mechanism of a medium-Mn advanced high strength steel (AHSS) over a temperature range from 25 degrees C to 400 degrees C has been studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the microstructures of specimens after the tensile test at different temperatures. Four deformation mechanisms were found, namely deformation-induced martensitic (DIM) transformation, deformation-induced bainitic (DIB) transformation, deformation twinning and dislocation glide. Among these deformation mechanisms, DIM and DIB were very effective mechanisms to contribute work hardening. The product of ultimate tensile strength (UTS) and total elongation (TEL) of the AHSS reached a value higher than 65 GPa%, when these two mechanisms occurred. The highest UTS x TEL value of 84 GPa% was obtained at 150 degrees C. From the results of the present research, it is suggested that warm working is a good processing route for obtaining a combination of high strength and high ductility in medium-Mn AHSS.