Effect of Processing Route on the Microstructure and Tensile Properties of an Al and Si-Bearing Medium-Mn TRIP Steel Microalloyed with V

The effect of processing route on the microstructure and tensile behavior has been analyzed in a V-microalloyed medium-Mn steel containing 3.5 Al and 1.2 Si (in wt pct). To obtain four different microstructures, as hot-rolled (HR) band was divided into several parts and three of them were submitted to treatments consisting of annealing at 620 degrees C (HRA), warm rolling (WR), and warm rolling followed by annealing at 600 degrees C (WRA). Complex microstructures i.e., mixture of austenite, alpha ferrite, delta ferrite, and martensite in different amounts, were observed. Tensile tests show that the balance between these phases is the most important factor that contributes to the variation in the strength and ductility of this steel. At a given value of strain, the enhancement of strength observed in HR samples is related to the presence of a high amount of fresh martensite of up to 32 pct, while the higher total elongation to failure found in WR sample is associated to the presence of about 60 pct of retained austenite. Optimal mechanical properties have been achieved for the WRA sample with a yield strength of 808 MPa and an ultrahigh product of strength and elongation of approximately 59.5 GPa pct, which guarantee its usefulness for automotive applications.