The effect of the strain rate on the stress-strain curve and microstructure of AHSS

This paper presents investigations of the structural changes and flow stress of advanced high-strength steels (AHSS) subject to deformation at high strain rates, taking into account the transformation of retained austenite into martensite. TRIP690 and DP600 steel sheets were selected for the investigations. Steel HC380 was selected as the reference material. The investigations have shown that besides the thermodynamical stability of retained austenite, also the temperature (the higher, the higher the strain rate) generated due to plastic deformations influences the shape of the stress-strain curve. This is linked with the actual changes in temperature during deformation and in the ultimate structure of the investigated steels. Analyses of the specimens carried out using an SE detector and the EBSD method showed that the tempering process was initiated in the microstructure of the DP600 steel, owing to the heat released during the deformation of the specimens. Because of the delayed transformation of austenite into martensite, the tempering of the martensite was not observed during the deformation of steel TRIP690. (C) 2016 Elsevier B.V. All rights reserved.