Abstract
In the present study, the effect of post weld heat treatment (PWHT) on the microstructure and corrosion kinetics of butter welded Nickel Alloy 617 and 12Cr steel was investigated. Buttering was carried out on the 12Cr side with the Thyssen 617 filler metal. Furthermore, post weld heat treatment (PWHT) was conducted at 730 °C with a holding time of 4 h followed by furnace cooling. Optical Microscopy (OM) was conducted to study the microstructural evolution in dissimilar material welding as a result of PWHT. Moreover, Scanning Electron Microscopy with energy dispersive spectroscopy (SEM-EDS) was employed to determine the elemental concentrations in all important regions of the butter weld before and after the PWHT. In addition, the effect of PWHT on the corrosion kinetics of the butter weld was also investigated by potentiodynamic polarization measurements in 5 wt.% NaCl + 0.5 wt.% CH3COOH electrolyte at room temperature, 30 °C, 50 °C and 70 °C. The corrosion activation parameters were also determined for both the samples by using Arrhenius plots. The results revealed the higher susceptibility of corrosion of the butter weld after PWHT, which was attributed to the reduced Cr content in the heat affected zone of the 12Cr region due to the sensitization effect of the heat treatment, resulting in higher corrosion rates.
Highlights
The results revealed that Inconel 617/310 austenitic steel joints welded by using Inconel 617 filler metals demonstrated the highest solidification cracking resistance
Results and ToBase/Filler investigate the effect of post weld heat treatment (PWHT) on the microstructure evolution of the important constituents
The micrograph of the weld metal (Figure 2c) confirmed the presence of the dendrite grains with the largest grain size micrograph of the weld metal (Figure 2c) confirmed the presence of the dendrite grains with the compared to the other regions based on the highest tendency for grain growth due to maximum heat largest grain size compared to the other regions based on the highest tendency for grain growth due exposure
Summary
“Global warming is one of the most important issues mankind is currently facing. It is increasing day by day due to the burning of fossil fuels in very large amounts around the world to meet energy demands. In order to improve the efficiency of thermal power plants, there is the need for an appropriate material for the manufacturing of turbine rotor and blades, which can be utilized at extreme conditions i.e., above 700 ◦ C and 250 bar temperature and pressure, respectively. For this purpose, Nickel based alloys of grades 617, 625 and 740 are considered to be the most promising materials owing to their good mechanical and metallurgical properties [7,8]. The PWHT was carried out on the butter weld to relieve the residual stresses and its consequent effects on microstructure and corrosion kinetics were evaluated
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