Improved Mechanical Properties of Two Twinning‐Induced Plasticity Steels with Novel Grain Morphology

Abstract

The mechanical properties and microstructures of two high Mn austenitic steels with novel grain morphology prepared by directional solidification and warm forging are investigated and compared with common twinning‐induced plasticity (TWIP) steel with equiaxed grains (EGs). The directional solidified sample (DS) is composed of columnar grains with simplified grain boundaries mainly characterized by low‐angle boundaries (LABs) with a fraction of 0.886. The warm forged sample (WF) contains numerous fibrous‐liked grains and fine nearly equiaxed grains featured with dominate LABs and complicated dislocation substructure. The significantly improved elongation and energy absorption capability of DS compared with EG are ascribed to the larger dislocation mean free path together with better plastic deformation compatibility and synergy between and within grains of DS, respectively. The largest energy absorption efficiency with enhanced yield strength of WF is mainly attributed to numerous fine grains with dominated LABs and complicated dislocation substructure. Inhomogeneous deformation characterized by well‐developed twins structure with dense dislocation pileup occurs in some regions of WF. It will contribute to enhancing work hardening, leading to a relatively high uniform elongation and significant increased strength. On the contrary, it may easily cause severe stress concentration and promote the occurrence of necking followed by plastic instability.