Nitrogen diffusion in different microstructures of plasma nitrided CK45 steel

Abstract

In this study, the nitrogen diffusion in different microstructures of CK45 steel was studied. Different microstructures were achieved by different heat treatment cycles as annealing, normalising and quench tempering. After heat treatment, plasma nitriding was performed at 550°C temperature, nitriding times of 5 h, in a gas mixture containing 25 vol.-%H₂/75 vol.-%N₂ and DC pulsed plasma nitriding unit. The surface, cross-section and the thickness of diffusion and white layers of specimens were studied in terms of optical and scanning electron microscopy. Surface phases have been studied by X-ray diffraction analysis. Results showed that by normalising the samples, higher diffusion depths could be achieved and the white layer thickness would be also higher. Other results showed that core hardness of quench tempered specimens could decrease after plasma nitriding due to being subjected to nitriding process temperature.

Keywords:

• Plasma nitriding
• CK45 steel
• Diffusion zone
• Compound layer
• Microstructure
• Hardness