Effect of pulse plasma nitriding on tribological properties of AISI 52100 and 440C steels

AISI 52100 and 440C bearing steels were nitrided in conventional plasma (CPN) and pulsed plasma (PPN) consisting of 0.33 and 1 N2/H2 gas ratios at temperature of 500 degrees C for 4 h under a constant pressure of 5 mbar. The surface of nitrided steels was investigated using optical microscopy, X-ray diffraction (XRD) and microhardness. The tribological behaviour of plasma nitrided steels was studied by means of unlubricated ball-on-disc method under constant loads of 5 and 20 N, sliding speed of 0.3 m/s at room temperature. The SEM and EDS techniques were used to analyse the worn surfaces of the steels. The results showed that gamma'-Fe4N and alpha-Fe(N) were dominant phases for pulsed plasma nitrided 52100 and 440C steels, respectively and pulsed plasma nitriding slightly improved the wear behaviour of both steels.