Study of the Thermochemical Surface Treatment Effect on the Phase Precipitation and Degradation Behaviour of DSS and SDSS.

In this study, the effect of a plasma ion carburizing process to duplex and superduplex stainless steels (DSS and SDSS), at 925 °C for a long time, as thermochemical process influencing the microstructural evolution is presented. The objective is to analyse the diffusion elements' influence on the precipitation of secondary phases after additional short thermal treatment. A comparison among the different treatments was performed after the resulting microstructures were analysed by Field Emission-Scanning Electron Microscope. Precipitation of secondary phases-sigma (σ), chi (χ), nitrides and carbides-seemed to occur during the treatments in a similar way for both steels (DSS and SDSS), although they showed a different morphology and precipitation mode. General corrosion behaviour of untreated and treated samples was investigated by potentiodynamic tests in order to prove their corrosion resistance. It was found that an improvement of the surface protection after the plasma carburizing process occurred.