Effect of boron addition on surface properties in alloying of AISI 1020 steel by plasma transferred arc method

In this study, the surface of the AISI 1020 steel was alloyed with FeCrC, FeW, FeB ferroalloy powders mixed at different ratios in different heat inputs. Plasma transferred arc (PTA) welding method was used as surface alloying method. The surface alloying process was done at two different feed rates (0.15 m/min, 0.1 m/min) and three different currents (120 A, 140 A, 160 A) to obtain different heat inputs. The microstructures of the alloyed surface layers of the obtained samples were analyzed by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDS) methods. Microhardness measurements were performed at microhardness test device. The dry sliding wear and friction coefficient properties were determined using a block-on-disk type wear test device. Wear tests were performed at 19.62 N, 39.24 N, 58.86 N load and the sliding distance of 900 m. In the experiments, it was found that different microstructures were formed according to the powder mixture ratio and heat input change. Also it was seen that the size and distribution of the phases changed as the heat input changed. Phases such as M7C3 (M=Cr, Fe, W) carbide, M23(C, B)6 (M=Cr, Fe, W) carbide, (Cr, Fe)B boride, FeB boride and Fe2B boride were detected in the alloyed surface layers generally. The highest microhardness value was measured at 1668 HV on sample surface alloyed with (%wt.) 80FeCrC-10FeW-10FeB powder mixture at 0.713 kJ/mm heat input. The highest average microhardness value was measured at 1217 HV on sample surface alloyed with (%wt.) 50FeCrC-1-20FeW-30FeB powder mixture at 0.585 kj/mm heat input. The average microhardness value of samples surface alloyed with low heat inputs were determined to be generally higher. It was seen that the wear resistance of the samples surface alloyed with low heat inputs were higher. It was determined that the sample with the highest wear resistance was the sample surface alloyed with (%ağ.) 70FeCrC-30FeB powder mixture at 0.475 kj/mm heat input. It was determined that the coefficient of friction of the samples surface alloyed with high heat input were generally lower. It was found that as the load increased, the coefficient of friction changed more steadily and in a small range. Keywords: AISI 1020, Plasma Transferred Arc (PTA) Welding, Surface Alloying, Fe-Cr-W-B-C, Fe-Cr-B-C, Wear, Friction.