This study investigated the dependence of grain orientation on the hydrogen embrittlement (HE) characteristics of high-Mn twinning-induced plasticity steels. Single-crystal micropillars were fabricated to represent the five major texture components of face-centered cubic structure: brass, Goss, copper, cube, and S components. These were classified into three groups for discussion based on the microstructural and mechanical characteristics. The copper and cube micropillars showed the lowest HE resistance because of an exclusive formation of twin boundaries that led to a localized hydrogen concentration. Brass and Goss micropillars revealed multiple slips with increasing strain, which was different from the case of S orientation that exhibited the activation of single slip system. The results of this work suggest that increasing frequency of S component grains would enhance HE resistance owing to the inhibited twinning and suppressed dislocation mobility. This is supported by the superiority of S/cube bicrystal micropillar to Goss/cube micropillar in terms of HE resistance.

Increasing the yield stress of twinning-induced plasticity (TWIP) steels is a demanding task for modern materials science. This aim can be achieved by microstructure refinement induced by heavy straining. We feature the microstructural evolution and mechanical performance of a high-manganese TWIP steel subjected to deformation treatment by different combinations of equal channel angular pressing (ECAP) and rolling at different temperatures. The effect of microstructure on the tensile properties of the steel subjected to the multi-pass ECAP process and to subsequent rolling is reported as well. We show that the combined deformation procedure allows us to further increase the strength of the processed workpieces due to a gradual transition from a banded structure to a heterogeneous hierarchical microstructure consisting of fragments, dislocation configurations and nano- and micro-twins colonies. Rolling of multi-pass ECAP specimens at 375 °C allowed us to achieve an extraordinary strength, the highest among all the investigated cases, while the best trade-off between yield strength and elongation to failure was reached using multi-pass ECAP followed by rolling at 500 °C. This study shows a great potential of using combined deformation techniques to enhance the mechanical performance of TWIP steels.

No abstract

This study examines the effect of Type-B liquid metal embrittlement (LME) cracks on high-cycle fatigue resistance of a spot-welded plate of transformation-induced plasticity (TRIP) steel. Tensile shear and cross tension were employed to simulate a spot-welded component subjected to a complex state of stress. Interestingly, neither the existence nor the depth of Type-B LME cracks changed the high-cycle fatigue resistance of the spot-welded samples under the two deformation modes tested. The finite-element analysis revealed the formation of maximum local stress at the sample notch, which acted as a crack-initiation site. It should be noted that this site was not changed even upon adding a Type-B LME crack to the simulation model.