Effect of Bainitic Transformation Temperature on the Microstructure and Mechanical Properties of A Trip Steel

The broad aim of the present study was to investigate the effect of bainitic transformation temperature on the microstructure and mechanical properties of δ-ferrite trip steel. in order to prepare the required samples, in this study, steel with the chemical composition of fe-0.25c-0.33si-1.05mn-4.56al was heat-treated after being cast and rolled. primarily each sample has been austenitized at the intercritical annealing temperature of 820°c for 600s and then was isothermally transformed in salt bath at the temperature range of 350-450 °c for 360s. the microstructure of each sample has been examined by the optical microscope. the microstructure of examined steels contain ferrite, bainite and residual austenite phases after the conducted heat-treatments. the amount of residual austenite as well as the residual carbon in this phase have considerable effect on strength and ductility of steel. the volume fraction of residual austenite and it’s carbon level were measured by x-ray diffraction analysis(xrd) which indicates that the lower the bainitic transformation temperature, the lower the residual austenite in the structure. the mechanical properties of the samples were examined and it has been concluded that the most appropriate combination of strength and ductility with the uts of 1050 mpa and elongation of 54% could be achieved in sample which was isothermally transformed at 400°c.