Abstract
This study investigated the microstructure of the dissimilar metal welding of Inconel 625 and AISI 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) processes with ERNiCr-3, TIG 316L and twisted (ERNiCr-3 and TIG 316L) fillers. Microstructure examinations were carried out using an optical microscope and Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray (EDAX). The results of the study showed the existence of a partially melted zone (PMZ) on the AISI 316L side. Weld zone (WZ) analysis showed the existence of a multi-directional grain growth on the 316L side in all specimens, although less growth was found on the Inconel 625 side. Grain growth almost disappeared using PCGTAW with twisted fillers. SEM/EDAX investigations indicated that secondary deleterious secondary phases were tiny and white in five experiments. However, a meager amount of precipitates occurred in PCGTA welding with twisted fillers. Moreover, these were particularly innocent precipitates, represented by black dots in images, whereas other tiny white secondary phases are known to be brittle. As a result, PCGTA welding with twisted fillers exhibited the best metallurgical properties.
Highlights
Inconel 625 is a nickel-based super alloy, which has good corrosion resistance properties at cryogenic as well as very high temperatures
Results showed that chemical composition was clearly changed in the fusion line and elemental transfer was obtained between the metals
The average weld hardness for PCGTA welding was found minimum in the root pass similar with Continuous Current Gas Tungsten Arc Welding (CCGTAW), with values 255.34 HV, 246.33 HV, 244.78 HV employing ERNiCr-3, TIG 316L and twisted fillers respectively
Summary
Inconel 625 is a nickel-based super alloy, which has good corrosion resistance properties at cryogenic as well as very high temperatures It is the preferred material in many heavy industries. It is used in the reactor-core of nuclear power plants, boilers, piping, exhaust systems of racing cars, impellers of chemical vessels, power plant turbine blades, aerospace engine components, etc. The bimetallic joints of Inconel 625 and austenitic stainless steel AISI 316 L are used in the chemical process at very high temperatures, especially the chromic acid calcining process, which contains a diluted acidic environment. One of the main reasons is that it reduces cost of materials, and the other is that it improves design as a result of operating environment requirements [12]
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