Development of high Mn–N duplex stainless steel for automobile structural components

A new high Mn–Ni free (duplex stainless steel) DSS containing 18Cr–6Mn–1Mo–0.2N has been developed by examining the effects of manganese on the corrosion and mechanical properties of high Mn SSs containing 18Cr–4 ∼ 11Mn–0 ∼ 2Ni–0 ∼ 1Mo–0.2N. The alloy with 45% ferrite is found to be an optimum alloy with much higher mechanical strength and similar corrosion resistance compared with those of standard SS304. In addition, the alloy was free of precipitation of sigma phase and Cr-nitride when exposed to high temperatures due primarily to relatively low contents of Cr, N and Mo. With an increase in Mn content, the resistance to pitting and metastable pitting corrosion of high Mn DSS decreased since the number of (Mn, Cr) oxides, acting as preferential sites of pitting, increased with the Mn content.