This study involves V-groove butt welding of CP Titanium to 304 stainless steel by the gas tungsten arc welding (GTAW) process without and with buttering layer at the 304 stainless steel base metal. ERCuSn-A and ERNiCu-7 were chosen as a filler metals. Investigations including visual testing (VT), microhardness testing and metallurgical analysis were carried out by means of variable welding parameters. The experimental results showed that using the ERCuSn-A filler metal without and with buttering layer, any surface defect was not observed in the dissimilar metals welded specimen but an underbead crack was found at weld metal adjacent to the Ti/weld metal interface. Using the ERNiCu-7 filler metal without buttering layer, linear porosity was observed at weldment. However, using ERNiCu-7 filler metal with buttering layer, defect-free welded specimen could be achieved. The results of EDS analysis indicated that at Ti/weld metal interface, Ti diffused from the Ti base metal to the weld metal. At 304 stainless steel/weld metal interface, Fe, Ni and Cr diffused from the 304 stainless steel base metal to the weld metal.
Single pass overlay welding of the ERNiCu-7 filler metal on the commercial pure titanium grade 2 and the 304 stainless steel using the gas tungsten arc welding (GTAW) process was studied. The ERNiCu-7 filler metal was overlay welded on the base metals with varying welding currents; it was 30A, 40A and 50A for the CP-Ti base metal and 50A, 60A and 70A for the 304SS base metal. The experimental results showed that the overlay CP-Ti welded-specimen, increasing of welding current increased bead width and decreased depth of penetration of weldment. While for the 304SS welded-specimen, increasing of welding current increased both bead width and depth of penetration. Suitable heat inputs to achieve good geometry of weldment for overlay welding were 348J/mm for CP-Ti welded-specimen and 558J/mm for 304SS welded-specimen.
Carbide-free bainite with filmlike retained austenite structure has been reported for its higher wear resistance and toughness compared with conventional bainite and pearlite structure. In order to take advantage from such beneficial structure, this study employs the surface welding method with self-shielded wire electrode containing low carbon (0.15 mass%), high silicon, and nickel on two pearlitic rail steels, R260 and R350HT. The preheating temperature and other welding parameters were carefully selected to avoid too high dilution, which leads to martensite formation. The weld metal, heat-affected zone, and base material were investigated by scanning electron microscopy. Microhardness and wear tests were carried out to ensure improved properties after the surface repair. The results show significant improvements in hardness and wear rate in weld metal compared with the base material.
This work studies the surface welding parameters for a practical repair for pearlitic rail grades: R260 and R350HT. A filler metal containing low carbon (0.15 %), high silicon (0.5 %) and nickel (2.5 %), self-shielded flux-core welding electrode (FCAW-S) is the candidate in order to ensure the preferable carbide-free bainite. The film-like morphology of the retained austenite is reported to promote the wear resistance and is ensured by silicon and nickel. The effect of preheat temperature and dilution on the microstructure and resulting hardness can be concluded. Too high dilution, as a result of high current and travel speed, and the reheating during the welding of the second layer can result in martensite formation and too high hardness. Proper control of the dilution ensures satisfactorily hardness and avoids martensite formation.
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