Influences of dislocation configuration and texture optimization on obtaining exceptional cryogenic strength-ductility synergy in a dynamic-recovered heterogeneous high-manganese steel

Abstract

In this study, an innovative strategy of dislocation configuration and texture optimization is employed to achieve a heterogeneous dynamic-recovered (DRV) high-manganese steel via successive cold-warm-rolling (CWR). Compared with single-step warm-rolling (WR) treatment, the imposed cold deformation of CWR process not only results in more and finer dislocation cells in DRV grains, but also leads to texture optimization with intensity weakening and component changing. Hence, the CWR sample shows a higher yield strength (YS, ∼1.35 GPa) and ultimate tensile strength (UTS, ∼1.6 GPa) without sacrificing the tensile elongation (TEL, ∼57%) at LNT (liquid nitrogen temperature), accompanied with a significantly lower mechanical anisotropy. The exceptional cryogenic strength-ductility synergy can be attributed to following: i) the difference of YS comes from the additional Taylor hardening effect (∼150 MPa); ii) the prefer-orientated DRV grains with a high Schmid factor (SFR) of twinning induces the twin deflections or kinks at the dislocation boundary in the early deformation stage; and iii) the refined cell structure can increase the critical resolved shear stress (CRSS) of twin, act as twin nucleus and impede its growth, leading to the occurrence of high-density of nano-twin segment (thickness: ∼15 nm, number density: ∼1.1 × 10⁸ m^-3) at a high stress and strain level. Thus, the cooperative forest dislocation hardening (∼870 MPa) and dynamic Hall-Petch strengthening (∼220 MPa) effects can provide continuous strain hardening capacity. In contrast, the high ductility of the WR sample primarily originates from the abundant microband-induced plasticity correlated with limited twinning- (TWIP) and transformation-induced plasticity (TRIP) due to a coarse twin (∼22.5 nm) and martensite thickness (∼55 nm).