Abstract
When a sulphur bearing gas is added to the nitrogen– hydrogen atmosphere used in a plasma thermochemical treatment, a nitrocarburising process can be performed because of the contribution from the carbon in the steel. In the present work, H2S has been used to introduce sulphur species into the discharge atmosphere. The sulphur promotes the nucleation of the 8 phase. A compound layer of thickness 30–45 μm with a duplex structure can be produced by this procedure on plain carbon steel and low alloy steel substrates. The outer zone (10–12 μm) is pure ε phase and the innermost zone consists essentially of γ’ phase. The influence of the gas composition, temperature, and duration of the treatment on the microhardness profiles and thickness of the compound layer has been investigated. Wear tests, using a plain carbon steel substrate, revealed significantly better wear behaviour of the sulphur bearing nitrocarburised specimens, compared with materials treated by conventional plasma nitriding.
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