Effect of Mo on intergranular corrosion behavior in super-austenitic stainless steel.

The effect of the Mo element on the intergranular corrosion behavior was investigated on super-austenitic stainless steels. The σ-phase structure and compositional changes of stainless steels with different Mo contents during aging at 800–900°C were investigated by TEM, combined with electrochemical tests, and two different intergranular corrosion mechanisms were revealed. The low-Mo 904 L stainless steel induces severe intergranular electrochemical corrosion due to selective anodic dissolution at grain boundaries caused by decreased passivation ability and σ-phase composition changes. The σ-phase precipitation of 254SMo and AL-6XN with high-Mo leads to Cr and Mo depletion reduces passivation film continuity, and causes intergranular corrosion. • Aging coarsens the σ-phase at grain boundaries in super austenitic steels with higher Mo content. • Low Mo austenitic steels face intergranular corrosion from weakened boundary passivation. • High Mo steels suffer intergranular corrosion from Cr/Mo depletion and erratic passivation. • Precipitate morphology and composition significantly alter intergranular corrosion. [ABSTRACT FROM AUTHOR]