In situ neutron diffraction study on microstructure evolution during thermo-mechanical processing of medium manganese steel

Nakamura, Yoshihiko*; Shibata, Akinobu*; Gong, W.*; Harjo, S.   ; Kawasaki, Takuro   ; Ito, Atsushi*; Tsuji, Nobuhiro*

The microstructure evolution of medium manganese steel (Fe-5Mn-2Si-0.1C (wt%)) during thermo-mechanical processing in ferrite + austenite two-phase region was investigated by in situ neutron diffraction analysis and microstructure observations. When the specimens were isothermally held at a temperature of 700C, the fraction of reversely transformed austenite increased gradually with an increase in the isothermal holding time. However, it did not reach the equilibrium fraction of austenite even after isothermal holding for 10 ks. On the other hand, the fraction of reversely transformed austenite increased rapidly after the compressive deformation at a strain rate of 1 s at 700C and reached the equilibrium state during subsequent isothermal holding for around 3 ks.