Effect of Ni and Mn on the Mechanical Properties of 22Cr Microduplex Stainless Steel

The tensile properties of 22Cr-2Ni-4Mn-0.2N micro-duplex stainless steels with different Ni and Mn contents were investigated. Duplex stainless steels were vacuum induction melted and hot rolled, then annealed at 1,000-1,100°C, at which temperature both the austenite and ferrite phases were stable. The volume fraction of the ferrite phase was markedly affected by the alloying elements of Mn and Ni; 1 wt% of Mn was equivalent to 0.4 wt% of Ni. All of the steels tested at room temperature showed the common strain-hardening behavior, while the steels tested at lower temperatures (-30 or -50°C) showed a distinct inflection point in their stress-strain curves, which resulted from the transformation of the austenite to strain-induced martensite. The onset strain (ε₀) of the inflection point in the stress-strain curve depended on the M _d30 value of the steel. Testing at lower temperatures resulted in smaller ε₀ and consequently higher strengths and fracture strains ( _f). The tensile behavior was examined from the perspective of austenite stability of the micro-duplex stainless steels with the different Ni and Mn contents.