In-situ three-dimensional X-ray investigation on micro ductile fracture mechanism of a high-Mn steel with delayed necking effect

This study investigates the micro ductile fracture mechanism of a high-Mn steel with delayed necking effect (DN-HMn steel) under monotonic tension. A random-oriented micro-grain structure cooperating with intragranular twins in the DN-HMn steel contrib-utes to its high tensile strength of 880 MPa and high uniform elongation of over 55%, ac-counting for 92.8% of the total elongation. Three-dimensional (3D) visualization of the ductile fracture process is presented, and characteristics of void evolution are identified. It was observed that voids distribute and grow uniformly during deformation, with larger voids forming a double-helix spatial distribution pattern at high strain levels, which fits the principal shear stress trajectory. The number and volume of voids in the DN-HMn steel showed a significant increase, with the porosity increasing from 0.071%0 (initial state) to 1.580%0 (before fracture). Intervoid necking was found to be the mode of void coalescence, which occurred close to the necking strain of the sample. The DN-HMn steel demonstrated a significant volume expansion of 4.58% throughout the elongation process, which breaks the volume conservation law of classical metal plasticity theory. This study opens new perspectives for understanding the ductile fracture mechanism of this steel. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).