Abstract
Austenitic stainless steels have low corrosion resistance in applications where strong acids and vapors attack the surface, typically in food and chemical industries. This drawback can be improved by surface treatments. Salt bath, gaseous or plasma-based surface treatments are a diffusion process for improving the hardness of the surface layer of stainless steels without significantly affecting their corrosion resistance. Low temperature nitriding and carburizing process can form a diffusion zone or/and compound phase. The corrosion-wear resistance of austenitic stainless steels can also improve with low temperature plasma nitriding and carburizing. The effect of these treatments on hardness and corrosion resistance was investigated in this research. Optical microscopy and Vickers hardness test were used for the characterization of the surface and potentiodynamic tests were performed to determine the corrosion rate. The results show that the hardness of the kolsterised sample is higher compared to the plasma nitride one. Beside this property, the corrosion rate is similar, but pitting corrosion was observed on the surface, due to the Cr2N formation.
Highlights
Nowadays, the improvement of the corrosion-wear resistance of stainless steels is becoming popular research area in the industrial applications
The corrosion-wear resistance of austenitic stainless steels can improve with low temperature plasma nitriding and carburizing
2 Materials and methods AISI 316L type austenitic stainless steel was used for the experiments with the following chemical composition: Cr (16.7), Ni (9.84), Mo (1.95), C (0.02), and Fe for balance
Summary
The improvement of the corrosion-wear resistance of stainless steels is becoming popular research area in the industrial applications. Low temperature nitriding (below 450 °C) is one of the most widely used surface treatment process in order to improve the surface hardness and wear resistance of steels without the loss of corrosion resistance [1, 2]. The precipitation of chromium nitrides in the nitrided layer can be suppressed, such that a nitrogen supersaturated layer composed of a metastable phase, which is known as S-phase [4, 5]. In this case, the nitrogen is an interstitial atom in the austenite's face centered cubic lattice. The S-phase can occur in the patented kolsterising process, where the nitrogen is replaced by carbon
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