Due to high wear resistance, Cobalt-based alloys, such as Stellite12 (52Co30Cr8.5W), have presently been used as materials for hardfacing in several applications. Thermowell, a protecting part for thermocouple in petrochemical production, is also coated by Stellite12. Because of high deposition rate, the flux-core arc welding (FCAW) method was selected to be hardfacing process in the research. However, their welding parameters should be exactly controlled in order to obtain desired properties, depending on the microstructure of this material. The objective of this experiment is to study the influence of the FCAW parameters on the erosion resistance of AISI 304 (Fe-18Cr-8Ni-0.06C) welded by the cobalt base alloy filler, Stellite12 (Co-30Cr-8.5W-1.5C) as the hardfacing layer. The studied parameters were welding speed in the range of 2.1-8.5 mm s-1, and wire feed speed in the range of 42.3-67.7 mm s-1, leading to different heat inputs and cooling rates. The erosion resistance was investigated by using solid particle erosion test rig at ambient temperature. Surface characterization was then carried out by SEM equipped EDX and XRD. The results showed the relationship between erosion resistance and microstructure in welding and HAZ zone. The erosion resistance was depended on the formation of interdendritic phase in the welding zone. According to the surface examination, it was found that the formation of interdendritic, including size and shape played an important role on the erosion resistance. The heat input and cooling rate concerned with welding parameters was further discussed with the erosion behavior in this research.Keywords Stellite12, Cobalt base alloys, Flux-core arc welding, FCAW, Erosion-resistance

Solid particle erosion on surface of material effects on life time for them such as the turbine brade, boiler tube and chemical processing equipments. Thermal spray is one of various technique which used for the repairing or building up new surface. The objective of this experiment is to study the influence of thermal spray Ni-Si-B coating parameters on the solid particle erosion resistance at room temperature. The coating parameters were the distances between coating nozzle and the substrate of 10, 15, and 20 mm and travel speeds of 1.0 and 1.5 mm s-1 respectively, leading to the difference of heat inputs. The hardness of coating surfaces was measured by Vickers hardness. The microstructure of coating surfaces was examined by using an optical microscope (OM) and scanning electron microscope (SEM). Moreover, solid particle erosion resistance of coating surfaces was investigated on the erosion test rig at room temperature. Erosion rates of specimens were assessed by the calculation of weight loss which measured using an electronic balance (0.1 mg resolution). The relationship between erosion resistance and hardness was studied coincide with the microstructure examination. According to the erosion resistance evaluation, it was found that an erosion rate of coating depended on the coating condition. Finally, wear scar morphology on the top of an eroded surface and cross-section area was observed by SEM. However, the coating parameters played an important role in the erosion resistance. The microstructure of coating concerned with coating parameters was further discussed with the erosion behavior in this research.