Role of carbon in improving the shape memory effect of Fe–Mn–Si–Cr–Ni alloys by thermo-mechanical treatments

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To clarify the role of carbon in improving the shape memory effect of Fe–Mn–Si-based shape memory alloys by thermomechanical treatments, we investigated the effect of optimum thermomechanical treatments on shape memory effect and microstructures of Fe–14Mn–5Si–8Cr–4Ni and Fe–14Mn–5Si–8Cr–4Ni–0.12C alloys. The Cr23C6 particles in optimum thermomechanical-treated Fe–14Mn–5S–8Cr–4Ni–0.12C more effectively prevented collisions between stress-induced ϵ martensite bands than the residual α′ martensite in optimum thermomechanical-treated Fe–14Mn–5Si–8Cr–4Ni. This result is attributed to the thinner width of stress-induced ϵ martensite bands in optimum thermomechanical-treated Fe–14Mn–5S–8Cr–4Ni–0.12C compared to optimum thermomechanical-treated Fe–14Mn–5Si–8Cr–4Ni. In addition, the Cr23C6 particles formed at more sites and provided more obstacles as compared with the residual α′ martensite. Accordingly, the recovery strain of Fe–14Mn–5Si–8Cr–4Ni–0.12C was higher than that of Fe–14Mn–5Si–8Cr–4Ni. It is concluded that carbon addition is beneficial to further improving the shape memory effect of Fe–Mn–Si-based shape memory alloys by thermomechanical treatments.