Real Time Observation of Martensite Transformation for a 0.4C Low Alloyed Steel by Neutron Diffraction
32 Pages Posted: 25 Sep 2019 Publication Status: Accepted
A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during fast cooling and during the ausforming process. The hkl diffraction intensity of austenite increased at the beginning of transformation due to the primary extinction effect. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. Ausforming slightly increases the Ms temperature, the amount of retained austenite at RT and the austenite lattice parameter. The dislocation densities in martensite and the retained austenite estimated using the convolutional multiple whole profile fitting method increase by ausforming.
Keywords: Martensite transformation, In-situ neutron diffraction, Ausforming, Low-alloy steel, Lattice parameter
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