Kinetics of the γ → ε Martensitic Transformation in Fine-Grained Fe-26Mn-0.14C Austenitic Steel

Effect of cooling rate on (ε, α') martensite formation in twinning/transformation-induced plasticity Fe-17Mn-0.06C steel

“…Hamada et al 14 worked on a high-Mn (Fe-26Mn-0.14C) austenitic steel hot compressed at 900, 1000, and 1100 °C with a strain rate of 5 s -1 followed by air cooling (AC) or water quenching (WQ). The occurrence of dynamic recrystallization (DRX) produced a fine grain size (~10 mm), which was found to prevent α' and ε martensite transformation upon cooling.…”

“…The grain boundaries, twins, and stacking faults enhance or suppress the phase transformation, 29,30 depending on the size of the grains. For the hot-rolled samples, rolled the grain size was reduced to ~100 µm (Figure 6a), well above the critical size (10 µm [14] ), thereby allowing the formation of up to 58% volume fraction of α' and ε martensite ( Table 2). …”

“…The latter depends on the steel chemical composition, temperature, austenite grain size, and amount of stress applied to the steel. The formation of martensite can be induced thermally or by applying strain [10][11][12][13][14] . During cooling, the austenitic Fe-Mn steel, within a restricted range of chemical composition, partially transforms into ε hcp and α' bcc martensite, while retaining some the untransformed austenite [12][13][14][15] .…”

“…The formation of martensite can be induced thermally or by applying strain [10][11][12][13][14] . During cooling, the austenitic Fe-Mn steel, within a restricted range of chemical composition, partially transforms into ε hcp and α' bcc martensite, while retaining some the untransformed austenite [12][13][14][15] . Stacking faults and twinning are important for the formation of martensite in Fe-Mn-Si-Al steels because they act as nucleation sites for martensite formation [16][17][18][19] .…”

“…α' martensite is formed either directly from austenite or at the intersections of different variants of ε martensite 8,9,20 . In addition to the cooling rate and crystallographic defects, the prior austenite grain size (PAGS) is another parameter that controls the stability of the austenite, because the formation of martensite can be prevented by the presence of a large numbers of barriers in the microstructure, such as twin or grain boundaries and deformation defects 11,12,14 . The industrial production of TRIP and TWIP steels always involves thermo-mechanical processing such as hot rolling, cold rolling at room temperature, and annealing.…”