Sulfocarbonitriding of steels with a low-carbon martensite structure

Saturation of steels with interstitial elements in a liquid phase allows creating gradient layers at relatively low temperatures and short durations of the treatment. Rather cheap and ecologically safe compositions for low-temperature nitriding and carbonitriding baths have been developed at the end of the last century. Improvement of tribotechnical characteristics can be achieved by adding a small amount of sulfur. Layers that have been formed at a low temperature after short-term treatment yield in thickness to those produced by a customary high-temperature long-term thermochemical treatment, and the necessity of subsequent quenching in liquid media creates additional technological and ecological difficulties with processing traditional steels. The use of low-carbon martensitic steels provides noticeable advantages. The activation energy of nitrogen diffusion in a low-carbon martensite is lower in comparison with that in a predominantly ferrite structure, and the quenching of low-carbon martensitic steels does not require the use of liquid cooling media. Austenitizing before quenching improves the uniformity of distribution of alloying elements in a gradient layer and increases its thickness ( to several hundreds of microns) due to postnitriding.