Abstract
The most effective method to reduce CO2 gas emission from the steam power plant is to improve its performance by elevating the steam temperature to more than 700 °C. For this, it is necessary to develop applicable materials at high temperatures. Ni-based Alloy 617 and 12Cr steel are used in steam power plants, due to their remarkable mechanical properties, high corrosion resistance, and creep strength. However, since Alloy 617 and 12Cr steel have different chemical compositions and thermal and mechanical properties, it is necessary to develop dissimilar material welding technologies. Moreover, in order to guarantee the reliability of dissimilar material welded structures, the assessment of mechanical and metallurgical properties, fatigue strength, fracture mechanical analysis, and welding residual stress analysis should be conducted on dissimilar material welded joints. In this study, first, multi-pass dissimilar material welding between Alloy 617 and 12Cr steel was performed under optimum welding conditions. Next, mechanical properties were assessed, including the static tensile strength, hardness distribution, and microstructural analysis of a dissimilar material welded joint. The results indicated that the yield strength and tensile strength of the dissimilar metal welded joint were higher than those of the Alloy 617 base metal, and lower than those of the 12Cr steel base metal. The hardness distribution of the 12Cr steel side was higher than that of Alloy 617 and the dissimilar material weld metal zone. It was observed that the microstructure of Alloy 617 HAZ was irregular austenite grain, while that of 12Cr steel HAZ was collapsed martensite grain, due to repeatable heat input during multi-pass welding.
Highlights
Environmental pollution from energy generation is a topical issue worldwide
There are four ways to improve this problem: the first is to generate energy from renewable energy resources, the second is to use nuclear energy, the third is to use carbon capture and storage before pollutants are released to the atmosphere, and the fourth is to increase energy efficiency by using A-USC thermal power plants that are capable of generating energy at temperatures above 700 ◦ C [1]
It brings a wide variety of other outstanding properties, e.g., high temperature oxidation resistance due to added aluminum, and solid solution strengthening due to cobalt and molybdenum content [7]
Summary
Environmental pollution from energy generation is a topical issue worldwide. There are four ways to improve this problem: the first is to generate energy from renewable energy resources, the second is to use nuclear energy, the third is to use carbon capture and storage before pollutants are released to the atmosphere, and the fourth is to increase energy efficiency by using A-USC (advanced-ultra super critical) thermal power plants that are capable of generating energy at temperatures above 700 ◦ C [1]. A-USC thermal power plants have improved thermal efficiency, and reduced CO2 emissions [2,3] At this elevated temperature, it is very difficult to find applicable materials that can withstand extreme environments. Ni-based super alloys and high chromium steel are suitable candidates for such extreme environments in the power generation industry due to their exceptional metallurgical stability at high temperatures, and excellent mechanical properties, such as high creep rupture strength, and good oxidation and corrosion resistance [4,5]. Alloy 617 is primarily known for its remarkable metallurgical stability [6] It brings a wide variety of other outstanding properties, e.g., high temperature oxidation resistance due to added aluminum, and solid solution strengthening due to cobalt and molybdenum content [7]. A dissimilar material welding between Alloy 617 and 12Cr steel was carried out using Direct Current Straight Polarity (DCSP) tungsten inert gas (TIG) welding technology, and an assessment of the mechanical properties and a microstructural analysis of the dissimilar material weld were performed
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