Effect of post-oxidizing on tribologieal and corrosion behaviour of plasma nitrocarburized AISI 4140 steel

摘要

AISI 4140 steel was initially plasma nitrocarburized at 570 and 700 °C for 4 h in a gas mixture of 60 % N_2 + 37 % H_2 + 3 % CO_2. After nitrocarburizing, post-oxidation treatment was performed at 450 °C for 1 h using oxidation gas mixture ratios of 50 % H_2 + 50 % O_2 and pure oxygen. The structural, mechanical, tribologieal, and corrosion properties of nitrocarburized and post-oxidized steel were analysed using an X-ray diffraction, microhardness tester, scanning electron microscopy, pin-on-disc tribotester, and electrochemical polarization. The experimental results showed that oxide layer included Fe_2O_3 and Fe_3O_4 phases while the compound layer formed after both ferritic and austenitic nitrocarburizing consisted of Fe2-3(N,C) and Fe_4(N,C) phases. Post-oxidation treatment improved further tribologieal and corrosion properties in consequence of nitrocarburizing. The contribution of post-oxidation treatment made after the ferritic nitrocarburizing was much more than the contribution of post-oxidation treatment made after the austenitic nitrocarburizing. Furthermore, it was seen that using hydrogen in oxidation gas mixture had useful effects such as better tribologieal properties and corrosion resistance.