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.

Estimation of the activation energy for surface diffusion during metastable phase formation

“…It has been reported that XRD is not able to detect grain boundary segregations or complexions [51][52][53]. It has been shown that the phase boundaries are changed compared to the generally accepted phase diagrams for example in Cu-Bi [54,55], W-Ni [56] and Mo-Ni [56] by as much as 0.08 at.% Bi, 0.31 at.% Ni and 1.7 at.% Ni, respectively.…”

X-ray diffraction study on the microstructure of a Mg–Zn–Y alloy consolidated by high-pressure torsion

“…It is noted that oxide phase was not detected by X-ray diffraction either in the initial powder or in the consolidated specimens which can be explained by its small fraction (0.2-1% as calculated from the particle size and the oxide layer thickness) and/or its amorphous state. Additionally, the observation of this oxide phase is more difficult if it does not form dispersoids during sintering but rather remains in the form of a thin grain boundary layer, similar to carbides in steel after HPT [36] or MnO in Mn-doped nanograined ZnO [37].…”

Effect of Large Shear Deformations on the Fracture Behavior of a Fully Pearlitic Steel

“…[19][20][21] This can be related to the fact that the maximum investigated strains were not large enough to induce a dissolution. The maximum nominal shear angle c investigated in this study was approximately~28 (e vM~1 6), whereas the largest nominal shear angle investigated in Reference 19 was approximately c~400.…”