Characterization of the metastable austenite in low-alloy FeCMnSi TRIP-aided steel by neutron diffraction

The detailed analysis of X-ray diffraction data obtained from intercritically annealed and isothermally transformed low-alloy FeCMnSi TRIP-aided steels reveals that the microstructure contains athermal plate martensite and Fe2C eta carbide in addition to ferrite, bainite and residual austenite. Neutron diffraction shows that athermal plate martensite can be formed at room temperature in the isolated austenite phase. Whereas the formation of athermal martensite leads to compressive strains in the austenite, the formation of strain-induced martensite results in tensile straining of the austenite. The strain-induced transformation leads to the formation of a martensite of low tetragonality. Low-temperature annealing leads to the formation of eta carbide in both the athermal and strain-induced martensite.