Effect of creating Vanadium Nitride Composite Coating through Flux Cored Arc Welding on the hardness of Carbon Steel

Surface hardening is one of the most popular ways for improving surface properties. In this research, surface hardening operation on low carbon steel was investigated via formation of vanadium nitride. To do so, three weld layers with 4, 3 and 2 passes on the surface of St37 steel were cladded by using flux cored arc welding via flux cored electrode containing 17% vanadium element. For investigating surface hardening and identifying the formation of vanadium nitride, hardness measurement test, x-ray diffraction and optical microscope were used. Obtained result from x-ray diffraction showed the formation of vanadium nitride and iron nitride precipitants. It was also found that these nitrides are main factor in surface hardening of low carbon steel. The result of hardness measurement showed that with increasing distance from base metal surface, the hardness has increased from 163 HV for base metal to 365 HV on surface. Microstructure investigation demonstrated that vanadium nitride precipitation was prevented to grow initial austenite and was caused the formation of finer ferrite in the microstructure of weld layers and consequently, the improvement of properties.