Production of Nb-doped super duplex stainless steel based on recycled material : A study of the microstructural characterization, corrosion, and mechanical behavior

• The corrosion behavior of a new Nb-doped stainless steel (SDSS-Nb) designed by the CALPHAD method, produced using an open atmosphere process based on recycled materials, was investigated to improve the circular economy. Three heat-treatment conditions were evaluated to assess the sensitization effects of the precipitates and inclusions. XRD and SEM-EDS were used for phase identification, and sensitization was analyzed by cyclic polarization and Scanning Kelvin Probe Force Microscopy (SKPFM). The thermodynamic stability predicted by Thermo-Calc agrees with that observed by SEM-EDS. It was observed by cyclic polarization that the corrosion sensitization was mainly provided by the σ phase, which was deduced from the results obtained by SEM-EDS, XRD, and Thermo-Calc simulations. Furthermore, it was obtained that the sensitization due to Cr2N precipitates and nonmetallic inclusions was low, and the mechanical response is comparable to commercial UNS32750 super duplex stainless steel, which allows a good performance in severe environments and an efficient industrial application. Additionally, it has been obtained by SKPFM that the shear potential between the σ phase and the austenite is between 210 mV and 241 mV and that its value depends on the stability and equilibrium reached by the σ phase during thermal cycling.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Cyclic polarization curves

Microstructural characterization

SKPFM

Super duplex stainless steel

Thermo-Calc modeling

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