Studies on tungsten carbide hardfacing of stainless steel by plasma transferred ARC welding

Abstract

Hardfacing is applied for the purpose of reducing wear, abrasion, impact, erosion, galling, or cavitation. This process is widely used to repair the railway rolling stock, earth moving and agricultural machineries, large gear wheels, conveyor shafts, chutes, turbine parts and innumerable other components. Plasma transferred arc hardfacing was selected for the present study. In hardfacing of stainless steel by PTAW, an attempt was made to study the various aspects of hardfacing such as regression modeling of weld bead geometry, optimization, microstructure, microhardness, macrohardness, and erosion resistance of hardfaced plates. The experiments were conducted using an automatic PTA hardfacing system. Test pieces of size 100 mm X 76 mm X 25 mm were cut from stainless steel plate and its surfaces were ground to remove oxide scale and dirt. Using those regression models the optimum percentage dilution was found by keeping depth of penetration, height of reinforcement and bead width as constraints and the corresponding process parameters were estimated. This was carried out using Microsoft Excel Solver. Using those optimum process parameters, the stainless steel plates were again hardfaced. Vickers microhardness measurements were carried out on specimens hardfaced at low, medium, and high heat input and optimum dilution conditions. Erosion experiments are carried out using an air-jet erosion test rig with silica erodent. The effect of varying the impingement angle on the erosion rate of hard facing was determined. The hardfaced specimens under low, medium, and high heat input and optimum dilution conditions were studied. The erosion rate of hardfacings are higher than that of base metal. All the above analysis and results on tungsten carbide hardfacing are very useful for the manufacturing industries for predicting weld bead geometry, hardness and erosion rate. These results are very useful to improve the hardfacing quality with required wear resistance. newline