INVESTIGATIONS ON HARDFACING CHARACTERISTICS OF NI-BASED ALLOY ON ASS 304 USING PLASMA TRANSFERRED ARC WELDING AT DIFFERENT SPEEDS

AISI 304 stainless steel is one of the most commonly used austenitic steel in various industries such as petro-chemical, nuclear plant, food, bio-medical, due to its desirable bulk mechanical properties such as high toughness, corrosion resistance, etc. However, it lacks the surface properties such as wear resistance and hardness which is critically required in severe working conditions. Hardfacing is an effective method to increase the surface properties, without disturbing the bulk mechanical characteristics. Among other coating techniques such as MIG, FCAW, laser cladding and so on, Plasma transferred arc welding can be considered superior in terms of bond strength, controlled dilution and high deposition rate. Due to the formation of high hardness and wear resistance coating quality, single layered Ni-Cr-B-Si alloy is coated over AISI 304 using plasma transferred arc welding process in present work. Among various process parameters, travel speed directly affects the rate of heat input and rate of overlay deposition which determines the cooling rate which influences microstructure, coating thickness and dilution. In this work, effect of travel speed was observed on coating microstructure, microhardness, wear resistance and dilution. Slurry abrasive wear test was performed to evaluate the wear resistance of the coating, by measuring the weight loss at various travel speed. Wear resistance was observed to be improved by a factor of about 4 as compared to the substrate material which shows a decreasing trend as we increase the travel speed. The microhardness of the coating was observed to go as high as 500 HV for certain travel speed. Dilution was observed to be ranging between 18% to 32% which increases with travel speed because of low heat input at higher travel speed. The microstructure investigation shows formation of a dendritic structure of borides and carbides, which was concluded to be the reason behind the obtained high hardness. Formation of Ni- γ phase was also observed on the top layer of the coating microstructure.