Surface alloying of high-vanadium high-speed steel on ductile iron using plasma transferred arc technique: Microstructure and wear properties

Highlights: • PTA technique was used to synthesize alloyed HV-HSS layer on ductile iron from preplaced V-Cr-Ti-Mo powders. • Spheroidal VC particles dominate in the PTA alloyed layer. • Reinforcement of micro-sized carbides makes the HV-HSS alloyed layer ultra-hard yet tough. • Wear tests confirm excellent tribological performance of the HV-HSS layer. A high-vanadium high speed steel (HVHSS) alloying layer was synthesized from pre-placed powders (V-Cr-Ti-Mo) on ductile iron (DI) substrate using plasma transferred arc (PTA) technique. The PTA-alloyed layer, characterized by microhardness, optical microscopy, XRD, EDS enabled SEM, TEM and pin-on-disk tribometry, consists of three main regions: top alloyed zone (TAZ), intermediate remelted zone (IRZ), and heat affected zone (HAZ) of the DI substrate. A large number of globular carbides particles with size smaller than 5 μm form in the TAZ through in-situ reactions between the alloying elements and graphite in the molten pool. Further microstructural characterizations indicate that the carbides are primarily vanadium carbide (VC), confirming the formation of the HVHSS layer. The maximum microhardness of the PTA-alloyed sample occurring at the subsurface is 950 HV_0.2 which is 5 times that of the substrate. The HVHSS layer exhibits superior tribological performance in comparison to PTA-remelted DI, Mn13 steel and DI substrate. The enhanced performance is attributed to the formation of mixed hard-phases such as MC, M₇C₃, M₂₃C₆, martensite and grain refining through rapid solidification accompanying the PTA process.