Abstract
This work is aimed to develop and optimize a gas ferritic oxynitrocarburizing treatment applied to an industrial 16MnCr5 component. The main effort has been to reduce the treatment time and the gas consumption by using a nitriding atmosphere that comprises nitrous oxide and ammonia. Special attention has been paid to improve the salt spray corrosion resistance with respect to the hardness requirements and the whole compound zone depth. Several changes have been applied to a base treatment by modifying the time and the temperature of each process phase, as well as the gas mixture and the flow of the nitrocarburizing atmosphere. Microhardness investigations and measurements of the compound layer's depth have been carried out on the treated specimens in order to evaluate the influences due to the variations of the process variables during the nitrocarburizing process. The introduction of nitrous oxide and ammonia allows reducing the nitriding time from 3 to 2 hours, and the purge time can be significantly reduced. Moreover, the increase of the nitrocarburizing temperature from 550 to 580°C allowed reducing the time of this phase from 4 to 3 hours. The post-oxidation time was moved from 3 to 4 hours in order to increase the thickness of the surface oxide layer and to improve the corrosion
Highlights
Mechanical and electrochemical properties of a metal surface largely determine the technological area where a particular industrial component could be used
At higher temperature, it was possible to reduce the cycle time from 4 to 3 hours (Treatment A2) without any significant loss in the hardness (Figure 3a). These results suggest how, in the analyzed working range, the hardness is strongly influenced by the temperature reached during the nitro-carburizing process more than the holding time
The effects of temperature, holding time and gas mixture applied during an oxy-nitrocarburizing treatment on the hardness and corrosion resistance properties in a 16MnCr5 component have been investigated
Summary
Mechanical and electrochemical properties of a metal surface largely determine the technological area where a particular industrial component could be used. There are many ways in order to improve the mechanical, tribological and corrosion properties of steel, such as adding various alloying elements in the material or modifying the steel surface by various thermochemical treatments [1]. The oxy-nitrocarburizing process allows improving mechanical and corrosion properties of steels through thermochemical surface modifications. There are several technological solutions which allow to oxy-nitrocarburize steel components, such as gaseous, plasma and salt bath treatments [1,2,3]. A gaseous oxy-nitrocarburizing treatment consists of several steps under different gas atmospheres. This type of treatment comprises a nitriding or nitro-carburizing stage followed by a post-oxidation step
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