Abstract
Cast austenitic stainless steel (CASS) often contains high contents of silicon, phosphorus, and sulfur to prompt low melting phases to form in the welds. As a result, welding defects can be induced to degrade the welds. This study’s purpose was to investigate the effects of electromagnetic stirring (EMS) on the CASS weldments. The results showed that the ferrites in the heat affected zone (HAZ) had tortuous grain boundaries, while those that were close to the fusion lines had transformed austenites. EMS could reduce the influence of the welding heat to make the grain boundaries less tortuous and the transformed austenites smaller. Although their temperature profiles were almost the same, the gas-tungsten-arc-welding (GTAW) weld had smaller grains with massive ferrite colonies and more precipitates, while the GTAW+EMS weld had denser ferrite colonies with multi-orientations, but fewer precipitates. The hardness of the base metals and HAZs were typically higher than that of the welds. For both of the welds, the root was the region with the highest hardness. The hardness decreased from the root to the cap regions along the thickness direction. The GTAW weld had a higher hardness than the GTAW+EMS weld. At room temperature, the GTAW+EMS weld had a higher notched tensile strength and elongation than the GTAW weld. This could be attributed to the observation that the GTAW+EMS weld had dense and intersecting dendrites and that more austenites were deformed during tensile testing.
Highlights
Cast austenitic stainless steel (CASS), with excellent mechanical properties and corrosion resistance, is a material that is often used for the essential components of pressurized water reactors (PWRs), such as reactor coolant pipes
The gas tungsten arc welding (GTAW)+electromagnetic stirring (EMS) weld had a higher notched tensile strength and elongation than the GTAW weld. This could be attributed to the observation that the GTAW+EMS weld had dense and intersecting dendrites and that more austenites were deformed during tensile testing
This study investigated the effects of electromagnetic stirring on the weldments of cast austenitic stainless steel
Summary
Cast austenitic stainless steel (CASS), with excellent mechanical properties and corrosion resistance, is a material that is often used for the essential components of pressurized water reactors (PWRs), such as reactor coolant pipes. With long-term operation at elevated temperatures, CASS components could be degraded by thermal embrittlement, affecting the safety of nuclear power plants, owing to the spinodal decomposition of ferrites [1]. The heat exchange tubes of PWR steam generators are made of Nickel-based alloy 600. These tubes are often plugged due to the leakage resulting from stress corrosion cracking (SCC) [2]. With an increase of plugged tubes, the efficiency of the power generation would suffer as a consequence. Welding CASS piping, a connection between hot/cold nozzles and the steam generator, is often performed to repair defected hot/cold leg welds or to replace inefficient steam generators with new ones
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