The strength–ductility trade-off has been a long-standing dilemma in materials science. This has limited the potential of many structural materials, steels in particular. Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off. After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction, we find that the yielding strength of the material can be doubled at no reduction in ductility. It is shown that this evasion of strength–ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation. A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention, and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems.
Twinning induced plasticity (TWIP) steels with excellent strength and elongation properties are expected to be the next generation of automotive high-strength steels. The present work investigates endogenous inclusions formed in Fe-25Mn-3Si-3Al TWIP steels in laboratorial ingot, mold casting after AOD steelmaking and electroslag remelting (ESR) process at industrial plant, respectively. The research shows that AlN and Al 2 O 3 inclusions are found as dominating inclusions, and most of them are AlN, but the number, distribution, size shape of inclusions have big differences in different metallurgical processes. The AlN inclusions in laboratorial ingot mainly present cluster states and have larger size, but after AOD or ESR process most of AlN inclusions are uniformly distributed, this would reduce harm to steel quality. From the point of view of thermodynamics, the research finds that the generation of AlN inclusions in Fe-25Mn-3Si-3Al steels is different from that of most of other high-Al steels or Al-killed steels, because many publications reported that the precipitation of AlN inclusions took place at solidifying front or solid phase, but AlN inclusions formed in Fe-25Mn-3Si-3Al steels generate in liquid steel, and related experimental results prove this point.
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