Revealing the mechanical properties and microstructure evolutions of Fe-22Mn-0.6C-(x)Al TWIP steels via Al alloying control

Three kinds of Fe-22Mn-0.6C-(x)Al (wt%) Twinning-Induced Plasticity (TWIP) steels were designed by changing the Al content. Uniaxial, unloading-reloading and stress-relaxation tensile tests were carried out to evaluate the mechanical properties. Meanwhile, electron channeling contrast imaging (ECCI), transmission electron microscopy (TEM) and X-ray tomography (XRT) techniques were used to investigate the microstructure evolutions. Firstly, it was found that the Al addition reduced the back stress level, suppressed twinning capability, and increased the stacking fault energy (SFE), leading to concession of work-hardening rates. Secondary, the Al addition improved the friction stress level and promoted the short-rang order (SRO) effect, which brought the transformation of dislocation slip from wavy to planar mode. Last but not least, the dynamic strain aging (DSA) effect brought the pinning of dislocations, forming high dislocation activation volume (> 100 b(3)). With increasing plastic strain, the deformation twins and SRO effect restricted dislocations gliding, resulting in low dislocation activation volume (< 50 b(3)). The present study could further illustrate the effects of SFE, SRO and DSA on the mechanical properties and microstructure evolutions of Fe-Mn-C-(Al) system TWIP steels via Al addition.