Investigation of Microstructure and Nitrided Layer Growth in Plasma Nitriding of Hot Work Tool Steel AISI H11 and Plastic Injection Mould Steel AISI P20

In this research two groups of samples including hot work steel H11 and plastic injection mould steel P20 were nitrided at 500 and 550°C for 5 and 10 hours at gas mixture of 50%H2-75%N2 by using pulsed direct current (DC) plasma nitriding apparatus. Thickness of diffusion zone and compound layer was measured by optical microscopy and scanning electron microscopy. The formed phases at surface were determined by X-Ray Diffraction (XRD). The results show that thethicknesses of both diffusion and compound layers, which are created in H11 steel, are greater than those of P20 steel. EDS analysis results from nitride layer demonstrated that up diffusion of carbon to the surface has occurred during plasma nitriding of the P20 steel, whereas this effect is not observed for the nitrided layer of H11 steel. XRD examinations revealed that the nitride layer of H11 steel was composed of two phases of γ′-nitride and ε-nitride, while the ε-nitride phase has been formed as the dominant phase in all time and temperature conditions of the process for P20 steel.

Keywords:

hot work tool steel , plastic injection mould steel , plasma nitriding , compound layer , diffusion zone