MICROSTRUCTURAL CHARACTERIZATION OF DC-PULSED PLASMA NITRIDED PLASTIC INJECTION MOULD STEEL P20

Ion nitriding improves the lifecycle of mould steels. In this research plastic injection mould steel P20 was nitrided at 450, 500 and 550°C for 2.5, 5, 7.5 and 10 hours at gas mixture of 25%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. Regarding to the results of diffusion thickness measures, values of Q and D0 for nitrogen diffusion in steel substrate were calculated as 44.246(kJ/mol) and 2.47×10-10(m2/s) respectively. Results have shown that by increasing treatment temperature and time, nitrided layer thickness increased respectively. According to micro hardness results, ion nitriding leads to improving the hardness of P20 up to 3 times. By increasing time and temperature, hardness and hardness depth also increases accordingly

Keywords:

plastic injection mould steel , Plasma nitriding , compound layer , diffusion zone