Investigation of the effects of shield gases and powders on the surface modification of a tig and plasma coated plain carbon steel

In this study, plain carbon steel surface were alloyed with different ferroalloys powders by using tungsten inert gas (GTA) and plasma transfer arc (PTA) welding processes. During the alloying process of specimens argon gas containing 3-5 % H2 was used as shield gas. The microstructures and abrasive wear properties of the alloyed and coated zones were investigated. In the experimental study, plain carbon steel (AISI 1020) surface were alloyed by using high carbon ferrochrome, ferrotitanium an ferromolybdenum powders. Following the surface alloying, conventional characterization techniques, such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction were employed for studying the microstructure of the alloyed zone. Abrasive wear tests were carried out at pin-on-disc apparatus. Hardness measurements were performed across the alloyed zone.As a result of surface alloying applications using GTA and PTA welding processes; modification operation was successfully carried out by using molten iron-based powders applied to bottom material surface at each of the two processes.Following the surface modification which had been done by using FeCr powder within the GTA and PTA processes, Cr7C3, eutectoid and Fe3C phases inside the dendritic structure in microstructure were observed. Whereas at surface alloyed with FeTi powder; FeTi, Fe3C and TiC phases were apparently formed inside the ferrite matrix. After the surface modification by using FeMo powder with the same methods again; Fe2Mo, MoC, FeC and Fe3C phases were observed inside the residual austenitic structure formed in microstructure.By increasing H2 ratio in shielding gas rather homogenous microstructure was reached with a resultant hardness increasing which was also monitored.It was observed that the highest hardness and wear resistance among treated specimens were obtained by using FeCr powder within PTA process, and it was followed with the same process produced specimens that were alloyed with FeMo and FeTi respectively.Keyword: Surface alloying, GTA, PTA, Abrasive wear, Shielding gas