Microstructural Damage Mapping on Heat-Resistant Steel Due to High-Temperature Fatigue

Abstract

This study aims to develop a damage map based on microstructure due to high-temperature fatigue load. To start with, Ni–Cr–Mo steel was used. The tensile and fatigue properties of it were investigated. The tests were performed at 750 °C. Microscopic evaluation after deformation revealed a variation of the damage mechanism, which was compared with damage map developed computationally. The dislocation activities that typically were homogeneously distributed at room temperature were localized near grain boundaries at elevated temperatures, similar to that of creep damage. A strong particle-dislocation interaction, usually called interfacial pinning, was observed and hereby mapped. Additional microstructural evolution such as the transformation of structure into coarse equiaxed grains and the carbide coarsening was also observed. A change in fracture mechanism from trans-granular at room temperature to intergranular fracture at elevated temperature similar to creep damage was also verified. The heart of this research was the ability to relate the finite element model that simulates both the equivalent stress and temperature distributions to the real experiment. Based on this estimation, the damage level was developed. Microstructural mapping corresponding to the damage level was subsequently made based on the experiment. It was concluded that the mapping was possible and this research could be thought as the embryo for the better understanding in damage theory bridging metallurgical approach to conventional approach using mesomechanics.