Effect of cooling rate after heat treatment on pitting corrosion of super duplex stainless steel UNS S 32750

In this study, super duplex stainless steel (SDSS) was heat-treated. The purpose of this study is to assess the effect of the cooling rate after heat treatment on the pitting corrosion of SDSS.

The heat treatment from 1,000°C to 1,300°C was applied to SDSS to check the effect of the cooling rate.

The heat treatment temperature produced a different SDSS microstructure, and the cooling rate led to the growth of austenite. The casted SDSS indicated the presence of heterogeneous austenite, and the precipitation secondary phase under 1.6 per cent precipitated to bare metal. By applying heat treatment and cooling SDSS, its corrosion resistance changes because of the change in the chemical composition. The cooling rate at 5,600 J/s has the highest critical pitting temperature (CPT) at 1,100°C, and the cooling rate at 1.6 J/s has the highest CPT at 1,200°C. Low cooling rate (0.4 J/s) made the secondary phase at all temperature range.

The effect of secondary phase not consider because that is well known to decreasing corrosion resistance.

Solution annealing is taken into account to optimize the corrosion resistance. But that is not consider the cooling rate at each temperature. This study assessed the effect of the cooling rate at each temperature point.

Manufacturers need to know the effect of the cooling rate to optimize the corrosion resistance, and this study can be applied in the industrial scene.

SDSS is hard the optimization because SDSS is a dual-phase stainless steel. Corrosion resistance can be optimized by controlling heat treatment temperature and the cooling rate. Anyone not studied the effect of the cooling rate at each temperature. The effect of the cooling rate should be considered to optimize the corrosion resistance.