Evaluation of the Microstructure and Mechanical Performance of an Advanced Ultra-High Strength TRIP1100 Steel Resulting from a New Thermo-Mechanical Treatment

This research investigates the effect of the rolling process and the new thermo-mechanical operation on achieving the microstructure of the high-strength and advanced TRIP1100 steel. The microstructure analysis of the resulting steel by scanning electron microscope showed a microstructure with a ferrite field along with the remaining bainite, martensite and austenitic phases. The grain size was obtained to be about 1 micron after the rolling process and the new thermomechanical operation. X-ray diffraction results also indicated 15% volume of the residual austenite for the 1100 TRIP steel. The tensile stresses of the specimens were evaluated and the strength of the samples was found to be higher than 1000 MPa; further, an extraordinary length was obtained for the 1100 TRIP steel. The results also showed that with adjusting the chemical composition and the newly proposed thermo-mechanical treatment, it was possible to achieve high strength in the 1100 TRIP steel with the flexibility of about 25% along with considerable work hardening. It was also found that at the angles of 45, 0 and 90, relative to the rolling direction, the behavior of this steel was almost the same; therefore, it could be widely used for shaping and welding. The analysis of fracture samples showed that the microphases grains had a relatively soft fracture; as well, fractures with almost co-axial dimples were observed, and the cavities had impurities that propagated cracking and fracturing during plastic deformation.