Abstract
AISI 316L steel was subjected to active screen plasma nitriding and nitrocarburising. The processes were carried out at 440 °C for 6 h. The nitriding process employed an atmosphere of nitrogen and hydrogen, while nitrocarburising was carried out in nitrogen, hydrogen and methane. The processes yielded structures consisting of nitrogen and nitro-carbon expanded austenite, respectively. Microhardness was measured via the Vickers method, surface roughness using an optical profilometer, microstructure by means of light microscopy, while a scanning electron microscope (SEM) served to determine surface topography. Phase composition, lattice parameter and lattice deformation tests were carried out using the X-ray diffraction (XRD) method. Corrosion resistance measurements were performed in a 0.5 M NaCl solution using the potentiodynamic method. The produced layers showed very high resistance to pitting corrosion, while the pitting potential reached 1.5 V, a value that has not yet been recorded in a chloride environment. After the passive layer was broken down, there was a clear deceleration of pitting in the nitrocarburised layer. It was found that in the case of nitro-carbon expanded austenite, pits are formed much slower compared to the nitrogen austenite layer.
Highlights
Austenitic steels are very popular metallic materials used in the chemical, food, automotive, nuclear and medical industries, to name a few [1]
Superaustenitic steels produce values of resistance to pitting corrosion that clearly exceed those of commonly used austenitic steels, which are not stabilised by nitrogen [5]
The use of active screen plasma processes makes it possible to produce an austenitic steel surface layer characterised by a significant increase in the durability of the passive layer over a broad range of potentials
Summary
Austenitic steels are very popular metallic materials used in the chemical, food, automotive, nuclear and medical industries, to name a few [1]. Similar or even better corrosion resistance results can be obtained by the application of low-temperature nitriding (
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