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A set of cast alloys was made by alloying 316L stainless steel powder with 5, 10, and 15 wt-% Mo to study the effects of the Mo content on the microstructures and corrosion behaviours. Sigma phases formed in all alloys and Laves phases co-precipitated in alloys with Mo additions of 10 and 15 wt-%. Alloys with higher Mo concentrations had greater volume fractions of both intermetallic phases, which contained higher Mo but lower Ni levels than the austenite. Potentiodynamic and potentiostatic tests were performed in pH 4 solution containing 10 mM NaCl to provide an aggressive chemical environment. All cast alloys had higher corrosion resistance than 316L SS. Electrochemical impedance spectroscopy showed the Mo content had a significant beneficial effect on the electrical properties of the passivating layers under highly oxidising conditions, but only a minor effect under moderately oxidising redox conditions. [ABSTRACT FROM AUTHOR]

Alloys were made by alloying 5, 10, 15, 17.5 and 20 wt-% Mo with Type 316L stainless steel. Sigma phases containing 21-29 wt-% Mo formed along the austenite grain boundaries with the addition of 5 wt-% Mo and increased with additions up to 15 wt-% Mo, but they decreased with further additions. Laves phases containing 33-40 wt-% Mo co-precipitated at additions of 10 wt-% Mo which increased with further Mo increases. The corrosion resistance, assessed by potentiodynamic polarisation in a 10 mM NaCl solution adjusted to pH 4, increased relative to Type 316L for alloys made with 5 and 10 wt-% added Mo, but decreased with further additions due to preferential corrosion of the Laves phase. The alloy made with 10 wt-% added Mo had the highest corrosion resistance due primarily to the high Mo content of the austenite. [ABSTRACT FROM AUTHOR]