The purpose of the paper is to clarify the serrated flow behavior and to explore the grain-size and strain-rate effects on serrations in coarse- and fine-grained FeMnC twin-induced plasticity (TWIP) steels at room temperature. Tensile tests were performed under extensometer-measured strain control, rather than under conventional cross-head displacement control, at strain rates ranging from 6 × 10-6 to 6 × 10~(-3) s~(-1). The results indicate that both the coarse- and fine-grained steels show different types of serrations, which depend on strain rate, and demonstrate a nonmonotonic strain-rate sensitivity of the critical strain for the onset of serrations, i.e., a positive strain-rate sensitivity of the critical strain in the high strain-rate region typified by type A serrations, and a negative strain-rate sensitivity in the low strain-rate region typified by type C ones. As compared to the coarse-grained steel, the fine-grained steel increases the critical strains, showing an inverse grain-size effect. The findings suggest that the fine-grained FeMnC TWIP steel suppresses the serrated flow, possibly due to the enhanced dynamic recovery associated with the decreased planar slip length in the fine-grained low stacking-fault-energy steel.
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