Steels containing high levels of Mn, Si and Al exhibit high plasticity when deformed, owing to twinning-induced plastitity (TWIP) and transformation-induced plasticity (TRIP) effects. In this study, we investigated the microstructural evolution of samples of samples of a 17%Mn steel subjected to war rolling at 700º and 800ºC. We also studied the effects of the microstructure of the steel samples on their mechanical behavior. Using a mathematic model the stacking fault energy of the steel was estimated to be 14.5 mJ/m². This value was indicative of a martensitic transformation. The presence of martensite and twinned austenite was verified using optical microscopy, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses. The presence of austenite and ε- and α'-martensites was confirmed using X-ray diffraction (XRD) analyses and dilatometry. Increasing the rate of cold reduction resulted in the formation of a α'-martensite phase and a decrease in the volume fraction of the ε-martensite phase. The volume fractions of the various phases were measured by integrating the areas under the XRD peaks. The sample subjected to a cold-rolling reduction of 81% and a subsequent annealing treatment did not contain a α'-martensite phase, indicating that it was fully recrystallized. The Vickers microhardness of the samples increased with an increase in the cold-rolling reduction rate. However, the microhardness values of the cold-rolled samples decreased after the annealing treatment.

The cooling rate, density of stacking faults, austenite grain size, and temperature strongly influence the γfcc → εhcp → a'bcc martensite transformation in austenitic alloys. During cooling, austenitic Fe-Mn steels can partially transform to ε and α'martensites within a restricted chemical composition. Martensite formation will influence the mechanical behavior of the alloy. The microstructure evolution under three cooling rates of a hot-rolled austenitic steel, Fe-17.0Mn-0.06C (wt%), was analyzed by optical microscopy and scanning electron microscopy/electron backscatter diffraction. The volume fraction of martensite and austenite were measured by X-ray diffraction line profile analysis by directly comparing the as-cast alloy, alloy subjected to different cooling conditions, and this processed with hot rolling.

A formação da austenita em condições isócronas em um aço de baixo carbono e microligado com Nb, a diferentes taxas de aquecimento e usando curvas dilatométricas, foi estudada utilizando o modelo de Johnson-Mehl-Avrami-Kolmogorov (JMAK), em conjunção com a relação funcional entre a energia de ativação aparente e a taxa de aquecimento. Mostrou-se que essa relação funcional é logarítmica e que a energia de ativação aparente diminui de 152,5 para 118,1 kJ/mol, quando a taxa de aquecimento aumenta de 0,1 para 16 K/s, para o expoente n da equação de JMAK igual a 1,0.

The austenite formation under isochronal conditions in Nb micro-alloyed low carbon steel was studied using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, for different heating rates and by means of dilatometric curves. The functional relationship between the apparent activation energy and heating rate was used in addition to this model. It was shown that this functional relationship is logarithmic and that the apparent activation energy decreases from 152.5 to 118.1 kJ/mol when the heating rate increases from 0.1 to 16 K/s, with the n exponent of the JMAK equation equal to 1.0.