Microstructure and wear properties of plasma nitrided low alloy steel tubes

Plasma nitriding is a surface treatment process, which can be applied on steel substrates with a wide variety of industrial applications. This study focuses on the properties of plasma nitrided low alloy steel of relatively long-small diameters tubes containing low amounts of Cr and Ni. The microstructure was investigated by using the optical microscopy (OM) and scanning electron microscopy (SEM). The results represented two nitride layers. In spite of the low amount of Cr and Ni, the compound layer demonstrated the maximum micro hardness of 800 HV. X-ray Diffraction (XRD) patterns, confirmed the presence of Fe3N(epsilon), Fe4N(gamma'), Cr2N, and Fe3NiN in the nitrided layer of samples. Wear properties were evaluated by pin on disc wear test under the loads of 10, 20, 30, 60, and 90 N, and sliding distance and velocity of 1000 m, and 0.3 ms(-1), respectively. Results showed that for 10 and 20 N loads the wear loss of nitrided samples was significantly lower than that of the uncoated ones; for 60 to 90 N loads the wear loss was slightly lower while under 30 N load the wear performance of nitrided sample was not as good as expected.