Investigation of the Effect of Boronizing Process on the Surface Properties of AISI 8740 Steel

Abstract

AISI 8740 is a low-alloy steel that contains elements such as Mn, Ni, Cr etc. It is frequently preferred especially in the aerospace industry. Boronizing (boriding) is a diffusion-based thermochemical process used to improve the surface properties of metals. Single or multi-phase boride layers can be obtained on the surface of ferrous and non-ferrous metals by boronizing treatment. Thanks to this process, low friction coefficient, high hardness, wear and corrosion resistance can be achieved on the material surface. In this study, it was aimed to improve the surface properties of AISI 8740 steel by boronizing. For this purpose, steel samples were boronized at 850oC, 900oC and 950oC temperatures for 4 hours by using a non-commercial boronizing powder mixture containing boric acid. The layers generated on the surface of steel samples boronized at the different process parameters were investigated in terms of microstructural and chemical properties. Microstructural examinations were performed with optical microscope (OM) and scanning electron microscope (SEM), the morphology of the formed layers was determined, and their thicknesses were measured. It was detected that the thickness of the boride layers increased with the increasing the processing temperature. The presence of phases in the boride layers was detected by X-ray diffractometry (XRD) and energy distribution spectrometry (EDS) analyses. In addition, the boride layers’ hardness was measured by performing microhardness tests. As a result, it was determined that the boronizing process was successfully performed and the surface hardness of the AISI 8740 steel increased significantly.