On the Relationship Between Microstructural Changes Induced During High Strain Amplitude Fatigue Loading and Fatigue Softening in Multiphase Medium Carbon Microalloyed Steel

摘要

Multiphase ferrite-bainite-martensite (F-B-M) microstructure was obtained in medium carbon V-microalloyed steels using a two-step cooling (TSC) and annealing procedure following by controlled forging (F) and rolling (R). In this paper, we describe electron microscopy study of multiphase steels (F-B-M (Forged) and F-B-M (Rolled)) steels subjected to low cycle fatigue loading at high strain amplitude. The microstructural changes induced during fatigue loading include deformation of bainite/marteniste laths, retained austenite strips, and precipitation of vanadium carbide occurs in addition to shearing of vanadium carbide precipitates. An attempt is made to explain the fatigue softening behavior in terms of microstructural changes.