Examination of Wear and Rockwell-C adhesion Properties of Nitronic 50 Steel Coated with Pack Boriding Method

Abstract

The Nitronic 50 steel is a nitrogen containing stainless steel, which has a high corrosion resistance, and high strength but its surface resistance against wear is low, making it extremely limited to use in areas subject to wear. In this study, in order to improve the material surface and to investigate its effect on tribological properties, boronizing process was carried out by used pack boriding method at 850 ° C, 900 ° C and 950 ° C for 4 hours. As a result of coating process, the boride layer has a smooth and flat structure in SEM investigations, the coating thickness varies between 9 µm and 36 µm and the boride layer thickness increases with increasing temperature. While the hardness of the uncoated material was around 250 HV0.05, the surface hardness of the material reached up to 1.712 HV0.05 with the coating process and increased about 7 times. According to XRD analysis, the surface of the coating layer consisted of phases FeB, CrB, Ni3B, Fe2B, Cr2B and MnB. Wear behavior was performed by ball-on-disk wear test in dry environment. The friction coefficient and wear rate decreases with increasing temperature, while the wear resistance is increased by 20 times compared to unboronized sample. When the wear tracks were examined, the uncoated Nitronic 50 had an adhesive wear mechanism, on the other hand the boronized samples had an adhesive and abrasive wear mechanism together. The Rockwell-C adhesion test was carried out under a load of 1.471 N and the resulting surface damages were evaluated according to the quality map. Boronized steel at 850 °C is defined as HF3 type, at 900 °C and 950 °C at boronized steel it is defined as HF4 type and adhesion is acceptable.