Dilatometric study of the phase transformations under conditions of recrystallized and non-recrystallized austenite in 3Mn–1.5Al steel

Abstract

This work presents the results of prior austenite state on the phase transformation behavior in a medium manganese steel alloyed with Al. The austenite was plastically deformed at two different temperatures. The first was at 1050 °C to ensure its recrystallization before cooling. The second treatment included deformation at 900 °C to keep high dislocation density in the austenite. The analysis of recrystallization process or its lack on the phase transformation behavior was analyzed. The study included thermodynamic calculations to analyze proper conditions of selected heat treatments. The dilatometric analysis of the phase transitions dependence on deformation temperatures was carried out. Deformation continuous cooling transformation diagrams were formed on this basis. The metallographic investigations were performed to determine microstructure constituents after cooling. The investigation proved the presence of ferrite untransformed during the austenitization step at 1100 °C. The dominant phase was bainite which was kept present up to 100 °C s−1 cooling rate. The amount of martensite increased with increasing the cooling rate. For the non-recrystallized austenite, more bainite was present in the microstructure for higher cooling rates compared to the recrystallized one. This was the result of higher density of preferable places for bainite nucleation in the non-recrystallized austenite. The Vickers hardness measurements were conducted after the applied heat treatments. The hardness of steel increased together with applying the higher cooling rates, which corresponded to the higher martensite amount. These values were higher for the non-recrystallized austenite because of higher dislocation density.

Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar

“…So thermal deformation causes a significant increase in the phase transformation temperature. On the other hand, when the deformed austenite undergoes recrystallization (at least partial recrystallization), the dislocation density decreases, the grain size refines, and the stability of the austenite after recrystallization is higher, thus prolonging the time required for the transformation to occur [31]. It can be seen from Figure 4 that there are more second-phase carbides precipitated in steel 2# at 1100 • C, which facilitates the further refinement of austenite grains during rolling and further improves austenite stability.…”

“…Due t effect of thermal deformation and further precipitation of Nb composite carbides stability of supercooled austenite reduces, and the free energy of the system incre which improves the driving force of austenite phase transformation [29,30]. So the deformation causes a significant increase in the phase transformation temperature the other hand, when the deformed austenite undergoes recrystallization (at least p recrystallization), the dislocation density decreases, the grain size refines, and the s ity of the austenite after recrystallization is higher, thus prolonging the time require the transformation to occur [31]. It can be seen from Figure 4 that there are more ond−phase carbides precipitated in steel 2# at 1100 °C, which facilitates the furthe finement of austenite grains during rolling and further improves austenite stab Therefore, the phase transition area of steel 2# in Figure 6b shifts downward.…”

3D Model of Heat Flow during Diffusional Phase Transformations

“…The historical development of the understanding of phase transformations in ferrous alloys was presented in the work of Hackenberg [ 7 ]. Among recent works related to experimental studies of phase transformations, the following can be mentioned: the theoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys [ 8 ], dilatometric study of phase transformations under conditions of recrystallized and non-recrystallized austenite in 3Mn1.5Al steel [ 9 ], solid–solid phase transformations and their kinetics in Ti-Al-Nb alloys [ 10 ], and the study of phase transformation and mechanical properties of ultrahigh strength steels under continuous cooling conditions [ 11 ]. An area that is also heavily explored is diffusional phase transformations, and, in recent years; for example, Kumar et al have studied the diffusional transformations using in situ cooling and heating techniques in a scanning electron microscope [ 12 ], while Mueller et al [ 13 ] have studied diffusional and partitionless ferrite-to-austenite phase transformations during intercritical annealing of medium-Mn steels.…”

“…The historical development of the understanding of phase transformations in ferrous alloys was presented in the work of Hackenberg [7]. Among recent works related to experimental studies of phase transformations, the following can be mentioned: the theoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys [8], dilatometric study of phase transformations under conditions of recrystallized and non-recrystallized austenite in 3Mn1.5Al steel [9], solid-solid phase Over the years, various experimental methods for studying phase transformations have been developed. In 1930, Davenport and Bain used the isothermal transformation as a technique to study phase transformations as a function of time and temperature [6].…”