α to γ transformation in the nanostructured surface layer of pearlitic steels near room temperature

An unusual low-temperature structural transformation from ferrite (α) to austenite (γ) is observed near room temperature through surface mechanical attrition treatment (SMAT) by means of transmission electron microscopy (TEM) and back-scattering Mössbauer spectroscopy (BSMS). Associated with the thermodynamic calculation, two factors that lead to the appearance of austenite after SMAT near room temperature are discussed. One factor is the formation of supersaturated nanocrystalline ferrite. The other is the compression stress at the boundaries of nano-size grains after SMAT.