Characterization of boride-rich hardfacing on carbon steel by arc spray and GMAW processes

This paper reports the hardfacing of low carbon steel using a boron-rich cored wire electrode. Arc spraying and gas metal arc welding (GMAW) techniques were employed to form a series of boride-rich coatings on the surface of St52 steel. Optical metallography, scanning electron microscopy, X-ray diffraction, and Vickers hardness testing were used to evaluate coatings structure and morphology, phase evolution and mechanical properties, respectively. The results showed that coatings produced by arc spraying composed of a uniform laminar morphology. In gas metal arc welding, a graded type coating was obtained and the microstructure consisted of a mixture of Fe2B, α-Fe and some FeB, with strong metallurgical bonding to the substrate. Identification of phases by XRD indicated that in both processes, the coatings possessed a high content of iron borides and some eutectic. These phases produced microhardness values in excess of 1600 HV on the coating surface. Indentation testing proved that boride coatings obtained by welding technique had better adhesion to steel substrate and were far more resistant to spalling.