Investigating Microstructure, Chemical Composition and Surface Layer Properties of Heavy-Duty Cast Iron After Nitriding

After nitriding heavy-duty cast iron we found light-coloured regions in the diffusion layer of the perlite metal base with graphite nodules. These resemble graphite in shape and form in its place. In order to determine if these light-coloured regions should affect properties and performance of components, we employed the Vickers microhardness test. The test result was low, merely 107 HV, which corresponds to ferrite. Such a soft structure in the diffusion layer of heavy-duty cast iron featuring graphite nodules contributes to improving component performance. This means we have to determine the morphology of this constituent. As a result, knowing its chemical composition allows us to study in detail the phases that form the light-coloured region structures. We used an electron microscope to determine the chemical composition and to conduct microscopic examination and X-ray crystallography of the nitrided layer surface in our cast-iron sample. We found that there are practically no graphite nodules in the diffusion layer. Electron microprobe mappings show that these regions contain iron, carbon and nitrogen; consequently, they are the ε-phase formed in place of the graphite nodules

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