The austenite reverse transformation behavior in a 1.5Mn-1.5Si-0.2C steel was in situ monitored using dilatometry, electron back scatter diffraction (EBSD), X-ray diffraction and neutron diffraction. The austenite reversion kinetics showed excellent agreements between dilatometry and neutron diffraction, whereas the austenite formation was observed to start at much higher temperature in cases of EBSD and X-ray diffraction measurements. Such discrepancy in transformation temperature is attributed to the change in chemical compositions near the surface of a specimen heated to elevated temperatures either in vacuum (EBSD) or in a helium gas atmosphere (X-ray); Mn and C concentrations were found to decrease with heating. In situ neutron diffraction enables us to investigate the changes in lattice constants of ferrite and austenite, showing not only thermal expansion but also suggesting carbon enrichment and phase stresses during the decomposition of the retained austenite and austenite reversion upon heating.
The phase transformation behavior from austenite upon cooling in a 1.5Mn-1.5Si-0.2C steel was in situ monitored using dilatometry, X-ray and neutron diffractions. The starting temperature of ferrite transformation was in good agreement between dilatometry and neutron diffraction, whereas much higher in X-ray diffraction. Such a discrepancy in transformation temperature is attributed to the change in chemical composition near the surface of a specimen heated to elevated temperatures in a helium gas atmosphere for X-ray diffraction. In situ neutron diffraction enables us to investigate the changes in lattice constants of ferrite and austenite, which are affected by not only thermal contraction but also transformation strains, thermal misfit strains and carbon enrichment in austenite. Pearlite transformation started after carbon enrichment in austenite reached approximately 0.7 mass% and contributed to diffraction line broadening.
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