Forming of Chromium-Nickel Surface Alloyed Layers in Steels by Methods of Thermo-Chemical Treatment

Processes of combined thermo-chemical treatment of carbon steels and of low-alloyed steels are studied. Processes include chromium-nickel diffusion metallization and nitriding. The idea consists in the forming of high-alloyed surface layers in steel parts working in the conditions of corrosion and/or wear. For metallization the method of thermo-diffusion saturation form metals suspensions was applied. The possibility of forming of the austenitic structure of the surface layer is shown. The subsequent nitriding (carbo-nitriding) processes in different regimes provide various phase composition of the diffusion layer. It was determined that for forming of wear resistant layer with enought ductility it is necessary to conduct the two-staged nitriding processes with injection of carbon-contatining compounds at the second stage. This leads to forming the composite structure: the carbo-nitrided layered zone at the surface with the thickness up to 40 micrones and the internal nitriding zone of quite uniform structure with the thickness of about 300...350 micrones. Such modified layers with the external carbo-nitrided zone contributes to the increase of wear resistance up to 10 times comparing to the items without surface treatment; friction coefficient decreases in 4..7 times.