Deformation Structures in High-Cycle Fatigue of 0.1N-32Mn-7Cr Steel at Cryogenic Temperatures

Abstract

Nitrogen-strengthened 32Mn-7Cr austenitic steel was cyclically deformed at various maximum stress amplitudes. The deformation structures induced by fatigue at cryogenic temperatures were examined by transmission electron microscopy. The dominant deformation mode was the {111}–<110> slip system, and dislocation motion was planar, especially at low stress levels. Cross slip of dislocations was strongly suppressed, and dislocation movements were restricted to their slip planes. At higher stress levels, mainly slip bands were observed. At lower stress levels, microslip or dislocation pile-ups were blocked or sharply localized at grain boundaries. Deformation twinning and E-martensite are not presumed to play a major role in the cyclic deformation.