Wear and corrosion behaviour of borided and nitrided m2 high speed steel

Abstract

Boriding and nitriding lead to improved tribological and corrosive properties of M2 high speed steel. Boronising treatment was carried out in Ekabor-II powders at the process temperature of 950 degrees C for 4 h. Gas nitriding was performed at 570 degrees C for 5 h with a gas mixture of 50% N-2 and 50% H-2. Structural and mechanical properties of borided and nitrided layers were characterised using X-ray diffrac-tion (XRD), optical microscopy and microhardness testing. Corrosion behaviour of borided and nitrided samples was also studied by the Tafel extrapolation and linear polarisation methods in 0.5 M NaHCO3 and 0.6 M NaCl solutions at 25 degrees C. Wear behaviour studies were carried out with a ball-on-disk testing method at a sliding speed rate of 0.3 m/s under 10 N loads in dry medium.

The existing phases on borided and nitrided M2 steels were FeB, Fe2B and Fe3N0.94, Fe4N, respectively. The present phases of nitride compounds in nitrided M2 steel were Fe3N and Fe4N. The lowest friction coefficient and the highest wear resistance values were measured in the borided specimens that were subjected to wear. Borided M2 samples show a lower corrosion current and higher corrosion resistance than the other samples. The lowest corrosion rate was obtained on borided samples in both solutions. As a result of boronising and nitriding, the low surface hardness, wear and corrosion performance of M2 steel was improved.