Strain Hardening, Damage and Fracture Behavior of Al-Added High Mn TWIP Steels

Abstract

The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m 2 and 29 mJ/m 2 . The evolution of microstructure, deformation mechanisms and micro-cracks development with increasing deformation was analyzed. Al-addition has led to the decrease of C diffusivity and reduction in tendency for Mn-C short-range ordering resulting in the suppression of serrated flow caused due to dynamic strain aging (DSA) in an alloy with 0.3 wt.% C at room temperature and quasi-static testing, while DSA was delayed in an alloy with 0.6 wt.% C. However, an alloy with 0.6 wt.% C showing DSA effect exhibited enhanced strain hardening and ductility compared to an alloy with 0.3 wt.% C without DSA effect. Twinning was identified as the most predominant deformation mode in both the alloys, which occurred along with dislocation glide. Al-addition has increased SFE thereby delaying the nucleation of deformation twins and prolonged saturation of twinning, which resulted in micro-cracks initiation only just prior to necking or failure. The increased stress concentration caused by the interception of deformation twins or slip bands at grain boundaries (GB) has led to the development of micro-cracks mainly at GB and triple junctions. Deformation twins and slip bands played a vital role in assisting inter-granular crack initiation and propagation. Micro-cracks that developed at manganese sulfide and aluminum nitride inclusions showed no tendency for growth even after large deformation indicating the minimal detrimental effect on the tensile properties.

Explanation of the PLC Effect in Advanced High-Strength Medium-Mn Steels. A Review

“…Al delays the reorientation of Mn-C point defect complexes by rising the process activation energy [28,[31][32][33][34]. Song et al [35] and Madivala et al [36] reported that some amount of Al addition could suppress the Mn-C formation in high-Mn steels. This might be the reason for the delay or absence of the serration phenomenon in Al-alloyed high-Mn steels.…”

Microstructure and Mechanical Properties of Gas Tungsten Arc Welded High Manganese Steel Sheet

“…For decades, high manganese steel has been studied for the application of automotive frame due to its excellent strength-ductility combination from the early stage of development [1][2][3][4][5][6][7]. Recently high manganese steel was tried to be applied for slurry pipes due to its excellent wear resistance.…”

Influence of Al Additions on the Microstructure and Mechanical Properties of a C and Si-Free High-Mn Steel

“…In addition to the grains presented in this figure, several other grains and orientations were checked, and no twinning evidence was observed. The overall mechanical behavior of all three alloys were similar regardless of their SFE value, especially the work hardening rate curve, which is highly associated to the dislocation structure and the high capacity of such materials to store dislocations [2]. The SFE for the 0Al alloy was predicted by thermodynamic modeling (31 mJ/m²) and determined experimentally (28 ± 9 mJ/m²), which is the lowest value amongst the alloys studied here.…”

“…High-Mn steels can be classified as Advanced High-Strength Steels (AHSS) and their development has been focused on understanding the exceptional mechanical properties, especially the ductility that can be achieved for such alloys [1,2]. The presence of plasticity-induced mechanisms has been described as one of the main contributions; however, the outstanding combination of high ductility and strength also arise because of the high capacity of the material to store dislocations in the microstructure [3].…”