Effect of prior annealing on the microstructure and mechanical properties of thermo-mechanically treated TRIP steel

Abstract

Low-carbon low-alloyed high strength steel 0.2C-1.5Al-0.5Si-2Mn-0.06Nb (in weight %) was forged into bars and annealed at 1050 °C with either 2-hour hold and furnace cooling to room temperature or with 20-min hold and controlled cooling by 1 °C/s. These various holds and coolings created two different initial microstructures, banded ferritic-pearlitic one for the long hold and bainitic-ferritic for the shorter hold and quicker cooling. Samples with those microstructures then underwent the same thermo-mechanical treatment (TMT) typical for TRIP (transformation induced plasticity) steels. Very different microstructures and mechanical properties were obtained for both initial states even after the application of the same TMT schedules. Light and scanning electron microscopy was used to characterize obtained microstructures and tensile tests were applied for the determination of mechanical properties.