Improvements in corrosion resistance,mechanical properties,and weldability of duplex austenitic/ferritic steels

The corrosion behaviour, toughness and weldability of duplex stainless steel can be improved by controlling the composition and austenite: ferrite ratio in the base metal and in the weld deposits. Addition of nitrogen is beneficial to ductility and restistance to pitting corrosion; the latter is also improved by increased chromium contents which stabilize the passive film. This effect is further enhanced by the addition of molybdenum which, however, should not exceed sigma phase at high temperatures. Copper in amounts up to 1.5% improves the resistance to marine environments; however, a certain upper limit should not be exceeded because of adverse effects on hot ductility. In view of the function of nickel concerning the austenite: ferrite ratio (which should be about 50:50) the nickel content should be appropriately selected and should be higher in the filter metal.