• 한국기계가공학회지
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• 제18권1호
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• pp.31-37
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• 2019

This study investigates the effects of long-term artificial-aging on hardness variation in the dissimilar metal weldments for nuclear power plant facilities. These dissimilar welds are inevitably required to join the components in nozzle parts of pressurized vessels, such as austenitic stainless steels and ferritic steels. A artificial thermal aging was conducted in an electrical furnace to simulate material degradation at high temperatures. The test materials were held at the temperature of $600^{\circ}C$ for 10000 hours and interrupted at various levels of degraded specimens. The degradation of hardness is a well-known phenomenon resulting from long-term aging or high-temperature degradation of structural materials. In this study, the variation of hardness at each position was different, and complicated in relation to microstructures such as twins, grains, precipitates, phase transformations, and residual stresses in dissimilar weldments. We discussed the variation of hardness in terms of microstructural changes during long-term aging.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.244-249
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• 2007

In several locations of the pressurized water reactors, dissimilar metal welds using inconel welding wires are used to join the low alloy steel nozzles to stainless steel pipes. To evaluate the integrity and design the dissimilar welds, tensile and fracture properties variations are needed. In this study, dissimilar metal welds composed of SA508 Gr.3 LAS, inconel 82/182 weld, and TP316 stainless steel were prepared by gas tungsten arc welding and shielded metal arc welding technique. Microstructures were observed using optical and electron microscopes. Different tensile and fracture properties were observed depending on the specimen sampling position at room temperature and $320^{\circ}C,$ and that was discussed based on the microstructure characteristics. It was found that the strength at the bottom of weld was greater than at the top of the weld. Also, from the test data using small punch specimen, more detailed tensile property variations were evaluated.

• Journal of Welding and Joining
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• 제29권2호
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• pp.56-63
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• 2011

his paper aimed to understand the residual stress in the dissimilar metal welds of nuclear power plant. Two kinds of residual stress were considered, which caused by welding and machining. Residual stress due to mechanical machining was measured by hole-drilling technique and x-ray diffraction method for the SA508 and F316L. Weld residual stress at dissimilar metal weld between SA508 and F316L was evaluated by FEA. Residual stress profiles were obtained for the inside surface and through thickness of welds. Machining effect was also analyzed by FEA. According to the residual stress measurement, it was observed that mechanical machining can generate tensile stress on the surface of the test material. However, FEA results showed that mechanical machining did not increase the tensile stress on the surface of weld region. Further study with more elaborate measurement and numerical analysis is required to identify the effect of machining on residual stress in the dissimilar metal weld region.

• 대한기계학회논문집
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• 제8권1호
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• pp.41-47
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• 1984

Increase of the requirements on quality of welded structures necessitates the improvement of known inspection methods and the introduction of progressive new techniques. Non-destructive methods are the most advanced, but there are considerable difficulties in using the methods of radiography with electromagnetic rays and ultrasonic testing in the inspection of dissimilar metal friction welds, because their physical and mechanical properties are changed very rapidly at the interface. The values of simple mechanical test for dissimilar metal friction welds have always been dubious, as the strength of the bond is often greater than that of the softer materials being jointed. Thus, in this paper some conventional mechanical testing methods are examined in an attempt to determine a technique for dissimilar metal friction welds, which will give a reliable quantitative indication of the weld quality. From the considered static and dynamic testing methods the impact bending test on unnotched and notched specimens are the most sensitive to find out the small joining defects in the interface.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1120-1125
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• 2004

Welding characteristics of STS304 stainless steel and Inconel 600 using a continuous wave Nd:YAG laser are experimentally investigated. Alloy 600 being used in steam generator tubing of pressurized water reactor(PWR) exposed to some corrosion environment, stress corrosion cracking can occur on this material. Presented here are the results from a series of experiments in which dissimilar metal welds were made using the gas tungsten arc welding process with pure argon shielding gas. But It is well known that solidification cracking susceptibility of austenitic alloys depends on the solidification temperature range and amount/distribution of solute rich liquid that exists at the terminal stages of solidification. An experimental study was conducted to determine effects of welding parameters and to optimize those parameters that have the most influence on eliminating or reducing the extent welding zone formation at dissimilar metal welds.

• 한국정밀공학회지
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• 제21권11호
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• pp.53-60
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• 2004

Laser welding techniques have been characterised for various materials. In this paper, the laser weldability of STS304 stainless steel and Inconel 600 at dissimilar metal welds using a continuous wave Nd:YAG laser are experimentally investigated. Inconel 600 is being used in a steam generator tubing of pressurized water reactor(PWR) exposed to some corrosion. Stress corrosion cracking can occur on this material. An experimental study was conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser were tested.

• 대한기계학회논문집A
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• 제37권5호
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• pp.649-655
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• 2013

이종금속용접부에 대한 실제 용접 공정 중 용접부에서 결함이 발견되면 이를 제거하고 보수용접이 수행된다. 일반적으로 보수용접을 수행하면 용접부에서 인장 잔류응력이 크게 증가될 수 있는 것으로 알려져 있다. 따라서 Alloy 82/182를 사용하여 보수용접이 수행된 이종금속용접부의 일차수 응력부식 균열 현상을 평가하기 위해서는 보수용접에 의한 용접부의 응력 변화를 정확하게 평가해야 한다. 본 논문에서는 비선형 유한요소해석을 수행하여 보수용접에 의한 원자력 이종금속 맞대기 용접부의 응력 분포를 평가하였다. 특히 보수용접 공정 모사를 위한 여러 유한요소 해석방법이 이종금속용접부의 응력분포에 미치는 영향을 평가하였다.

• 대한기계학회논문집A
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• 제36권2호
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• pp.137-148
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• 2012

가압경수로의 많은 관통관 중에서 니켈 기저 합금인 Inconel alloy 600 계열의 이종금속용접부는 일차수응력부식균열에 민감하며, 이를 평가하기 위하여 용접부에 작용하는 잔류응력분포를 정확히 예측하는 것이 중요하다. 본 논문에서는 유한요소해석을 이용하여 노즐 맞대기 이종금속용접부에 작용하는 일반적인 잔류응력분포를 예측하였다. 이를 위해 노즐 맞대기 이종금속용접부의 형상을 단순화하여 특정한 형상 변수에 따른 용접부 잔류응력분포를 확인하였으며, 이를 토대로 기존 문헌에 제시된 오스테나이트계 배관 맞대기 용접부 잔류응력 분포식을 수정하여 가압경수로 노즐 맞대기 이종금속용접부에 작용하는 일반적인 잔류응력분포 예측식을 제시하였다.

• Journal of Welding and Joining
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• 제35권3호
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• pp.68-74
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• 2017

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E71T-1C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, Intragranular polygonal ferrite and grainboundary ferrite were formed only in first layer of weld metal. Another layers consisted of acicular ferrite and $Widmannst{\ddot{a}}tten$ ferrite. The amount of acicular ferrite was increased with decreasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered martensite and lower bainite. Lower and upper bainite were formed in heat affected zone of carbon steel. Tensile strengths of dissimilar metal welds decreased with increasing heat inputs. Dissimilar metal welds showed a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals welds showed that the weight loss rate by corrosion below 170 hours was decreased with increasing heat inputs due to the increase of the amount of acicular ferrite.

• 한국압력기기공학회 논문집
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• 제9권1호
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• pp.70-76
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• 2013

Several finite element models for the leak-before-break (LBB) assessment of overlay dissimilar metal weldment were constructed and analyzed to develop a simple finite element modeling method. The J-integral, crack opening displacement (COD) and J-integral distribution along the crack front in thickness direction due to the applied moment were obtained from the analysis results of the constructed finite element models, and studied compared to the previous literatures. It is concluded that the modeling with base material only is simple and produces a slightly conservative results compared to the complex modeling composed with weld metal and base metal in the calculation of J-integrals and COD values which are used for the calculation of fracture toughness and postulated leakage crack length respectively.