Microstructural modification during isothermal ageing of a low nickel duplex stainless steel

In order to reduce the cost of duplex stainless steel (DSS), the Ni could be partially substituted by Mn and N, to maintain the alpha/gamma microstructure, the corrosion resistance and mechanical strength similar to the common Ni–Cr–Mo DSS. In this paper the microstructure stability, impact strength and the general corrosion behaviour of a low Ni grade, 22Cr–4Mn–0,2N DSS, were examined. In the solution annealing condition the corrosion resistance is quite similar to the austenitic grade. A moderate precipitation of nitrides and carbides was evidenced after isothermal treatment in the range 600–900 °C, while no dangerous topologically close packed phases (TCP-phases) were detected. The precipitation affects the impact strength, which decreases to about 50 J, while the corrosion resistance is less markedly affected.