Effect of Alternative Boronizing Mixtures on Boride Layer and Tribological Behaviour of Boronized SAE 1020 Steel

In this study, SAE 1020 steel samples were boronized at 850 °C for 4 h with different boronizing mixtures by powder-pack boronizing method. H3BO3 or Na2B8O13 was used as the boron source, KBF4 or NaBF4 was used as the activator and SiC was used as the diluent. Thus, 4 different boronizing mixtures (M1-M4) were prepared. Thickness, morphology and phase structure of the formed boride layers were studied by X-ray diffraction and microstructural analyzes. The single phase (Fe2B) boride layer with saw-tooth morphology was formed on surface of the samples. The thickest boride layers were obtained by using M1 and M2 boronizing mixtures. Microhardness measurements were performed to determine hardness of the 3 zones (core, transition zone and boride layer). The means of boride layer hardness of the samples were compared according to 95% Confidence Intervals analysis. It was determined that the average hardness value of the boride layers was about 1475 HV. Wear tests were fulfilled by ball on disc type wear test method under dry sliding condition and at 25 °C. According to the friction coefficient and specific wear rate values of boronized samples, it was identified that the sample SM4 boronized with M4 boronizing mixture has the lowest wear rate (1.64 mm3/N.m) and friction coefficient value (0.63).