Abstract
Nitrocarburizing is considered one of the most important thermochemical treatments for surface modification of metallic materials and involves the simultaneous diffusion of nitrogen and carbon onto the surface. Understanding and controlling the formation of the nitrocarburized layer have considerable industrial interest due to the improvements regarding wear, fatigue, and corrosion resistances. DIN 100Cr6 steel samples were treated by plasma nitrocarburizing for two hours, with two treatment temperatures (550 and 600°C) and four methane concentrations in the gas mixture composition (0, 1.0, 1.5, and 2.0%). SEM and XRD analyses, and wear resistance tests were used to characterize the samples. Results showed that the treatment temperature and atmosphere composition had considerable influence on the compound layer morphology. For nitrided samples the compound layer consists of γ'-Fe4N phase, and the presence of carbon in the gas mixture helps stabilize the ɛ-Fe2-3N phase. Higher CH4 concentration in the treatment atmosphere improve the sample superficial wear resistance.
Highlights
The plasma nitrocarburizing is a thermochemical process of surface hardening that uses a glow discharge to introduce nitrogen and carbon simultaneously onto the material surfaces 1,2
The addition of methane in the gas mixture increased the amount of carbon in the nitrocarburized atmosphere, and increased the ɛ-Fe2-3N phase amount in the modified surface layer, as reported in the literature . 22,23,26
The nitrogen and carbon mean concentration profiles of the nitrocarburized layer produced on DIN 100Cr6 steel at 550°C and 600°C are shown in Figs. 3 and 4, respectively
Summary
The plasma nitrocarburizing is a thermochemical process of surface hardening that uses a glow discharge to introduce nitrogen and carbon simultaneously onto the material surfaces 1,2. This process is usually recommended for carbon steels, as they do not have enough constituents to form nitrides such as other medium alloy steels 3. If the process occurs above the eutectoid temperature, it is termed austenitic nitrocarburizing, and there is a partial transformation of the ferritic matrix into the austenite phase, with the formation of three layers: the compound layer, the diffusion zone, and between these two layers, the so called transformed austenite layer. This austenite layer can transform into martensite during rapid cooling of the sample, thereby increasing the hardness in the region below the compound layer 1
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