Structure and Properties of Nanograined Fe–C Alloys after Severe Plastic Deformation

Abstract The microstructure and properties of several Fe–C alloys are studied in a) the as‐cast state, b) after a long annealing time at 725 °C, and, c) after high‐pressure torsion (HPT) The grain size after HPT is in the nanometer range. Only Fe₃C (cementite) and α‐Fe remain in the alloys after HPT. Less stable Hägg carbide and retained austenite disappear after HPT, and phase composition closely approaches the equilibrium corresponding to the HPT temperature and pressure. This HPT behavior differs from that associated with ball‐milling, which can lead to the formation of metastable or amorphous phases. Therefore, severe plastic deformation opens the way to produce materials with very stable phase structure and thus ensures the stable properties of nanograined steel during its life‐time.