Microstructure and mechanical property of the fusion boundary region in an Alloy 182-low alloy steel dissimilar weld joint

2010 ◽  
Vol 45 (19) ◽  
pp. 5332-5338 ◽  
Author(s):  
J. Hou ◽  
Q. J. Peng ◽  
Y. Takeda ◽  
J. Kuniya ◽  
T. Shoji ◽  
...  
Keyword(s):  
Mechanical Property ◽  
Alloy Steel ◽  
Weld Joint ◽  
Boundary Region ◽  
Low Alloy Steel ◽  
Fusion Boundary ◽  
Dissimilar Weld ◽  
Microstructure And Mechanical Property

A Study of Thermal Aging Effects on Microstructures of Dissimilar Metal Weldment

2013 ◽  
Author(s):  
Kyoung Joon Choi ◽  
Jong Jin Kim ◽  
Ji Hyun Kim
Keyword(s):  
Weld Metal ◽  
Alloy Steel ◽  
Thermal Aging ◽  
Base Alloy ◽  
Boundary Region ◽  
Low Alloy Steel ◽  
Aging Effects ◽  
Fusion Boundary ◽  
Dissimilar Weld ◽  
Dissimilar Metal

Characterizations of microstructure and mechanical property were conducted to investigate the effect of long-term thermal aging on the microstructural evolution in the fusion boundary region between weld metal and low alloy steel in dissimilar metal welds. A representative dissimilar weld mock-up made of Alloy 690-Alloy 152-A533 Gr. B was fabricated and aged at 450°C for 5,500 hours. It was observed that the region near the fusion boundary was generally divided into several regions including dilution zone in the Ni-base alloy weld metal, fusion boundary, and heat-affected zone in the low alloy steel. A steep gradient was shown in the chemical composition profile across the interface between A533 Gr. B and Alloy 152. The precipitation of carbides was also observed along and near the fusion boundary of aged dissimilar metal joints. It was also found that the precipitation of Cr carbides was enhanced by the thermal aging near the fusion boundary.

PWSCC Experience of Pressurizer Dissimilar Metal Welds at Tsuruga Unit-2

2004 ◽  
Author(s):  
Hiroyuki Kobayashi ◽  
Kimihito Takeuchi ◽  
Shohei Nakama ◽  
Masayuki Mukai ◽  
Takahiro Ohta
Keyword(s):  
Alloy Steel ◽  
Weld Joint ◽  
Repair Process ◽  
Visual Observation ◽  
Low Alloy Steel ◽  
Relief Valve ◽  
Metallographic Examination ◽  
Dissimilar Weld ◽  
Root Cause ◽  
Non Destructive

During the 13th refuel outage in September 2003, the small boric acid deposit was observed at one dissimilar weld joint between Relief Valve Nozzle and Safe End of Pressurizer in Tsuruga unit 2. The other four indications were also observed at the weld joint by non-destructive examination. Similar indications were also observed at Safety Valve Nozzle. Both Nozzles were under the steam condition at 345°C. As the first root cause investigation, the visual observation after etching was conducted at these weld joint on site. The observation revealed the repair weld print. Both weld joints with cracks were taken to conduct some investigations such as metallographic examination of fracture surface at hot laboratory. Hot laboratory examination results revealed that all cracks were extended axially in the Ni base metal weld joint, and there was no evidence of any cracks extending into the low alloy steel Nozzle and stainless steel Safe end. All cracks were interdendritic and branched. Metallographic examination results revealed that the crack growth mainly was caused by interdendritic stress corrosion cracking (IDSCC). These Nozzles including the weld joint with indications were repaired by jointing the spool piece as new Safe ends. The repair process includes the weld buttering on the low alloy steel Nozzle and joint welding between Nozzle and the spool piece. These welding were conducted by GTAW using alloy 52. It took twenty days to complete the repair works.

Investigation of Microstructural Changes due to Thermal Aging in Dissimilar Metal Welds

2014 ◽  
Author(s):  
Kyoung Joon Choi ◽  
Seung Chang Yoo ◽  
Chi Bum Bahn ◽  
Ji Hyun Kim
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Alloy Steel ◽  
Thermal Aging ◽  
Boundary Region ◽  
Low Alloy Steel ◽  
Chemical Gradient ◽  
Fusion Boundary ◽  
Dissimilar Metal

To investigate the effect of long-term thermal aging on the fusion boundary region between low-alloy steel A533 Gr. B and weld metal Alloy 152, a representative dissimilar weld mockup composed of Alloy 690/Alloy 152/A533 Gr. B was aged in laboratory furnaces under accelerated temperature conditions. The aging time was determined using the diffusion equation. The heat treatment was performed at 450°C for 60-y equivalent time (5,500 h) to simulate thermal aging effects. An additional aging heat treatment was also performed at 400°C for 15- and 30-y equivalent times (6,450 and 12,911 h, respectively) to determine the effects of temperature on aged microstructures. The characterization was mainly conducted in the microstructure of the fusion boundary region in the weld root region using scanning electron microscopy, transmission electron microscopy, and three-dimensional atom probe tomography. It was determined that the region near the fusion boundary was generally divided into several regions, such as a dilution zone (that included a chemical gradient in the weld side), fusion boundary, and heat-affected zone in the low-alloy steel. The results of this study showed that heat treatment increased Cr content in the dilution zone, but the chemical gradient in the weld side near the fusion boundary persisted. For the microstructure, it was observed that treatment induced the formation and growth of Cr precipitates in the fusion boundary region of the dissimilar metal joints due to the thermodynamic driving force. At two heat treatment conditions (400 and 450°C), although the extent of the results described above differed, the trend in the results appeared to be the same. This microstructure information can improve the understanding of cracking-resistant change when structural changes occur. Furthermore, such data will be important for assessing the effects of aging on structural components and for evaluating the long-term operation of nuclear power plants.

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