Abstract
In this work, a new type of δ-TRIP steel was designed. The fatigue limit and S-N curve were measured by the fatigue testing machine. The fatigue fracture was observed by the scanning electron microscope (SEM), and influencing factors of fatigue crack initiation were analyzed. The results show that the fatigue limit of δ-TRIP steel is 361MPa, and fatigue cracks are initiated on the surface of the sample. In the initial stage of fatigue crack initiation, the crack growth rate of the specimen is relatively slow under the action of stress. As the crack continues to expand, the magnitude and direction of the stress on the crack tip change and the stress situation becomes more complicated. The crack begins to branch and grows in different directions The metastable retained austenite in δ-TRIP steel undergoes phase transformation under the action of external force, which will absorb a lot of energy. At the same time, there are many large angle grain boundaries in the steel hindering the crack propagation. These two characteristics make the δ-TRIP steel has excellent fatigue performance.
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