Short‐term spinodal decomposition – its effects on corrosion behaviour of a duplex stainless steel and feasibility as a strengthening treatment

Abstract

The present paper looks into the effects of spinodal decomposition (SD) on the corrosion resistance and cavitation erosion behaviour of the duplex stainless steel (DSS) 7MoPLUS. SD takes place at 500 8C in the ferrite phase at the early stage of thermal ageing, with an attendant hardness increase. Nevertheless, thermal ageing at this temperature for up to 2 days nearly does not reduce pitting potential (in 3.5% NaCl). Surface integrity, however, is degraded by the appearance of noticeable pits after just a few hours of exposure to this temperature. Ageing for 1 week at 500 8C does not seem to alter the corrosion morphology of the ferrite phase in 1 M HCl. On the other hand, SD does bring about changes to the nature of passive film, as demonstrated by open-circuit potential measurements in 3.5% NaCl. The cavitation erosion (CE) resistance of 7MoPLUS is slightly enhanced by short-term SD treatment (for 5 h), as propagation of CE damage emanating from deformation twins in the ferrite phase is made less efficient. It is suggested that short-term SD treatment is a feasible strengthening method for DSSs.

Effect of heat treatment on the cavitation erosion resistance of stainless steel

“…Similar tendencies were also found for Grade 600‐3 SG iron, for which the cavitation erosion rate can be reduced by a factor of six after being treated by laser treatment . A moderate CER enhancement of duplex stainless steel 7MoPLUS was reported as a result of spinodal decomposition at 500 °C for 5 h . Previous studies also showed that the change of CER depends on the temperature employed in the heat treatment.…”

Literature Review of Phase Transformations and Cavitation Erosion of Duplex Stainless Steels

“…The G phase is usually very small in size, which is shown in Figure 6 for a duplex Figure 5. The ferrite and austenite of a grade 2205 duplex stainless steel after spinodal decomposition treatment [25].…”