Puspendu Sahu

Structure and microstructure evolution during martensitic transformation in wrought Fe–26Mn–0.14C austenitic steel: an effect of cooling rate

Structure and microstructure evolution under various cooling rates of a wrought austenitic steel, Fe-26Mn-0.14C (composition in mass %), were studied by the Rietveld method of X-ray diffraction pattern fitting, grain boundary characterization by electron back-scattered diffraction (EBSD) and optical microscopy. Cooling rate, density of stacking faults, and austenite grain size and grain boundaries influence the observed gamma(fcc) --> epsilon(hcp) transformation and lead to significant anisotropic X-ray line broadening. Depending on the cooling conditions, the grain boundaries are misoriented at both lower and higher angles. In the epsilon-martensites, the dominant planar fault is twins (similar to 10(-3)). The austenite grains were found to contain low to moderate density of stacking faults (similar to 10(-4)-10(-3)), which act as efficient nucleation sites of the epsilon-martensites. Both X-ray and EBSD analyses estimated negligible twins in the austenite. Approximate average dislocation densities have been estimated and correlated with the grain structure.

Evolution of Recrystallization Texture in AISI300 Series Austenitic Stainless Steels After Cold Rolling to Large Strain

The present paper deals with the evolution of texture in austenitic stainless steels during annealing after 95% cold rolling. After 95% cold rolling, the texture is mainly of the brass type {110} along with a scatter towards the S orientation {123} and Goss orientation {011} . Weak evidence of Cu component is observed at this high deformation level. During annealing, recovery is observed before any detectable recrystallization. After recrystallization, the overall texture intensity was weak; however, there are some discernible texture components. There was no existence of the brass component at this stage. Major components are centered on Goss orientation and Cu component {112} as well as the BR component {236} . Also, there are some few orientations which come up after recrystallization i.e. {142} and {012} . With increase in annealing temperature the textural evolution shows emergence of weak texture with another new component i.e. {197} . The evolution of texture was correlated with the deformation texture through twin chain reaction.

Studies on Martensite Transformation in a Metastable Austenitic Cr-Mn Stainless Steel

The influences of the heating rate and annealing duration on martensite formation and its reversion to austenite have been investigated in a 60% cold-rolled metastable high-manganese austenitic Type 204Cu stainless steel. A Gleeble 3800 thermomechanical simulator was used for dilatometric measurements. Cold-rolled steel pieces were either heated up to 1000 °C at various heating rates between 5 °C/s and 150 °C/s followed by quenching to room temperature, or heated and held at temperatures in the range of 450 620 °C for different durations between 0.1 600 s. In heating experiments, dilatation curves revealed an expansion of a specimen starting around 550 °C followed by contraction, both processes depending on the heating rate. These dimensional changes could be correlated to the formation and reversion of a ferromagnetic phase, α-martensite. Some martensite was also formed during isothermal holding in connection with tempering of the pre-existing α-martensite before the following reversion, as established by magnetic measurements. Tempering of martensite was revealed by microhardness behaviour, X-ray diffraction analysis and transmission electron microscopy.