The purpose of steel thermochemical treatments is to increase surface hardness as well as steel’s wear resistance. These treatments modify the surface layer chemical composition and morphology. Thermo-chemical treatments are given the following names, according to the main elements used as enrichment agents: carburizing and carbonitriding.
The surface carburizing of low-carbon steel components is carried out at a temperature generally within the range of 850 ° C to 950 ° C. The gaseous-type carburizing agent is able to ensure a carbon enrichment of the surface. The steel, having undergone this process, will achieve the required surface hardness through hardening and tempering treatments.
A thermochemical process for surface hardening similar to carburizing but carried out at a slightly lower temperatures (850-900 ° C) with the addition of ammonia to the carburizing gas. Nitrogen released by the dissociation of the ammonia molecule lowers the Ferrite- Austenite transformation limit and increases the hardenability of the work piece undergoing treatment.
Steel thermochemical treatments have the goal of making the surface very hard and, within certain limits, wear-resistant. These treatments have the purpose of modifying the composition of the steel’s surface layer. According to the main elements used as surface enrichment agents, thermo-chemical treatments are named as follows: gas nitriding, nitrocarburizing and Pronox®.
This is applied to steel and cast iron and is the thermo-chemical process involving surface hardening carried out in the ferritic phase at relatively low temperatures (550°C-580°C). The result is the diffusion of nitrogen and carbon in the surface layers.
This is applied to steels and natural cast iron and is a process involving surface hardening carried out in the ferritic phase at relatively low temperatures (480°C-570°C) in order to favour the diffusion of nitrogen.
The first Nitriding \Nitrocarburizing phase is useful for increasing the characteristics of hardness and wear and corrosion resistance followed by an Oxidation phase with the formation of a compact layer of iron oxide, which is useful for enhancing resistance to oxidation.