Wear Behavior of Hardfacing on 3.5% Chromium Cast Steel by submerged Arc Welding

Abstract

Hardfacing is an economical process for maintaining or repairing the engineering components due to wear problems. In this project, twelve samples of 3.5% Cr steel plates were hardfaced using austenitic stainless-steel buffer electrodes and martensitic steel hardfacing electrodes with a twin-wires submerged arc welding process. Identical welding procedures were repeated in all samples. The main objective of this research is to maximize wear resistance obtained in the hardfaced layer obtained by optimizing the welding parameters. The heat inputs for single layer and three layers hardfacing were varied using three different welding currents: 500A, 600A and 700A while keeping welding voltages and travel speeds constant; and two different welding polarities (AC and DC+). Single buffer layer was deposited on the base metal and preheating on the base metal plate at 350 °C was kept constant for all experiments. An optical microscope was used to analyze macrostructures and microstructures of the base metal, heat affected zone, buffer layer and hardfacing layers. The structures of single layer and three layers hardfacing and worn surfaces of the wear tested samples of three layers hardfacing were also taken using a scanning electron microscope (SEM). Chemical compositions of phases seen on SEM images were also determined using EDX. The amounts of martensite phase seen in the cross- sections and top surfaces optical micrograph of three layers hardfacing and dilution percentage of all samples were determined using Image J software. A Vickers hardness tester was used to measure microhardness values of the cross-sectional and top surface of the hardfaced samples. Wear resistance based on mass loss of the hardfaced samples was tested using a dry sand rubber wheel machine according to A of ASTM G65 standard procedure. The microstructural examinations showed absence of welding defects and good bonding between layers. Wear resistance results showed lower wear were found in samples welded using AC polarity. Also, those samples showed higher harnesses, dilution, the volume fraction of martensite phase compared to samples welded using DC+ polarity. Percent dilution correlated with hardness and microstructure of hardfaced layers. The microstructures and amount of martensite phase present influence the wear resistance of hardfaced layers. In addition, the abrasive mass loss of single layer hardfacing was higher than that of three layers hardfacing because the microstructure of single layer hardfacing showed higher amount of austenite phase due to the effect of dilution with austenitic buffer layer. In summary, the optimum procedure to get hardfacing wear resistance is to use 15 KJ/cm heat input obtained using 500A with AC polarity for both single layer and three layers hardfacing.