EFFECT OF HOLDING TIME ON MICROSTRUCTURAL EVOLUTION OF MEDIUM MANGANESE STEEL DURING INTERCRITICAL ANNEALING

The present paper investigates over the influence of annealing temperature and holding time on the micro structural evolution. It was found that the microstructure evolved from martensite structure into a structure consists of austenite and ferrite during intercritical annealing process. The improved ductility may be attributed to large volume fraction of austenite retained after intercritical annealing. A thermo dynamic model for the prediction of optimal annealing temperature and maximum retained austenite content has been thoroughly evaluated. For further characterization, scanning electron microscopy, EBSD, micro-hardness testing and Xray diffraction were carried out. The investigations manifested a pronounced influence of both annealing temperature and holding time, on the phase fractions of ferrite, austenite and martensite, which must be taken into account by designing batch annealing route for Medium-Mn TRIP (Transformation induced plasticity) steels in order to obtain superior combination of strength and ductility.