Microstructure and mechanical properties of a novel twinning induced plasticity steel with two different grain morphologies

Abstract

A novel heterogeneous-structure (HS) twinning-induced plasticity (TWIP) steel containing alternating columnar grain (CG) and equiaxed grain (EG) domains was successfully fabricated via prestraining, partial recrystallization, and directional solidification. Compared with the traditional EG sample, the HS sample exhibited a better tensile strength–elongation combination (yield strength ≈ 263 MPa, ultimate tensile strength ≈ 573 MPa, total elongation ≈ 101.5%). The mutually constrained structure could effectively control the unique deformation modes of the EG and CG domains at different deformation stages. The HS sample exhibited stable and continuous plastic deformation owing to the timely release of localized high strain or stress, postponed plastic instability, and restrained crack propagation owing to the constrained structure. The stress relaxation was due to twinning and the effects of geometrically necessary dislocations, which accommodated deformation incompatibility. The improved mechanical properties of the HS sample were due to the persistent occurrence of the TWIP effect under very low to high strain levels during the entire deformation process, the effective grain boundary hardening in the EG domain, and the additional work hardening provided by the GNDs.