scholarly journals Microstructure investigation on the fusion zone of steel/nickel-alloy dissimilar weld joint for nozzle buttering in nuclear power industry

2021 ◽  
Author(s):  
X. Guo ◽  
P. He ◽  
K. Xu ◽  
X. Ch. Lv ◽  
J. B. Zhang ◽  
...  
Keyword(s):  
Nickel Alloy ◽  
Fusion Zone ◽  
Nuclear Power ◽  
Filler Metal ◽  
Base Material ◽  
Face Centered Cubic ◽  
Dilution Ratio ◽  
Fusion Boundary ◽  
Solidification Temperature ◽  
Initial Solidification

Abstract Microstructure of the fusion zone of steel/nickel-alloy dissimilar metal welds (DMWs) for nozzle buttering was investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron back-scattered microscopy (EBSD). The results showed that the dissimilar joint was complete, without welding defects. The structures of the fusion zone included the beach structure along the fusion boundary, the peninsula structures connected with the fusion boundary, and the island structures in the weld. The distribution of these three types of structures near the fusion boundary was uneven. The beach structure was formed because of the insufficient mixing and solidification of the molten liquid base material and the filler metal, with the width ranging between 0 and 150 μm. The peninsula and island structures were formed by the undercooling of the insufficiently mixed liquid base material and filler metal that entered the weld because of the convection and scouring of the weld pool. The composition of the three structures depended on the degree of mixing of the liquid base material and the filler metal, with a dilution ratio between 40 and 60%. The degree of dilution for the beach, peninsula, and island structures decreased in turn. With an increase in the dilution ratio, the initial solidification temperature of the corresponding composition increased significantly. When the dilution ratio exceeded 94.5%, the initial solidification phase transformed from the face-centered cubic γ-austenite into a body-centered cubic ferrite, with island structures solidified in the form of ferrites in the weld near the fusion boundary. The austenite grain orientations at weld side are dispersed with 75% large (> 15°) misorientation in frequency and the overall texture orientation distributes dispersedly with deviating from the < 100 > direction.

scholarly journals Effect of Current on the Microstructural and Mechanical Properties of Mig Welded Aa6061 Aluminum Alloy

2020 ◽  
Vol 8 (5) ◽  
pp. 4727-4732
Keyword(s):  
Mechanical Properties ◽  
Aluminium Alloy ◽  
Fusion Zone ◽  
Filler Metal ◽  
Base Material ◽  
Thermal Conditions ◽  
Mig Welding ◽  
Metal Solidification ◽  
Columnar Grains ◽  
Aa6061 Aluminium Alloy

Aluminium and its alloy has very wide area of application i.e. aerospace, automobile and structural industries. The present investigation aimed to study the effect of MIG welding on microstructural and mechanical properties of AA6061 aluminium alloy. The characteristics of fusion zone is typical coarse columnar grains structure because of the prevailing thermal conditions during weld metal solidification. In this work, plates of 5mm thickness have been used as the base material for preparing single pass butt welded joints at different-different current values. The filler wire used for joining the plates is AA4043 (Al-5%Si by wt.) grade aluminium alloy. From this investigation, it was found that the hardness of fusion zone was degraded significantly due to usage of lower hardness filler metal. The precipitation evolution in the heat-affected zone was characterized by XRD which improves the tensile properties of the welded AA6061 alloy.

scholarly journals A Study on Determining Weld Joint Hardening and a Quality Evaluation Algorithm for 9% Nickel Weld Joints Using the Dilution Ratio of the Base Material in Fiber Laser Welding

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1308
Author(s):  
Minho Park ◽  
Jisun Kim ◽  
Changmin Pyo ◽  
Jaewoong Kim ◽  
Kwangsan Chun
Keyword(s):  
Laser Welding ◽  
Fiber Laser ◽  
Weld Joint ◽  
Base Material ◽  
Welding Process ◽  
Fuel Oil ◽  
Welding Quality ◽  
Dilution Ratio ◽  
Fiber Laser Welding ◽  
Evaluation Algorithm

The demand for LNG-powered ships and related equipment is rapidly increasing among major domestic and foreign carriers due to the strengthened IMO regulations on the sulfur content of ship fuel oil. LNG operation in a cryogenic environment requires a storage tank and fuel supply system that uses steel with excellent brittleness and fatigue strength. A ship using LNG is very sensitive to explosion and fire. For this reason, 9% Ni is often used, because ships require high quality products with special materials and structural technologies that ensure operability at cryogenic temperatures. However, research to derive uniform welding quality is urgent because the deterioration of weld quality in the 9% Ni steel welding process is caused by high process difficulty and differences in welding quality depending on a welder’s skill set. This study proposes a method to guarantee a uniform quality of 9% Ni steel in a fiber laser welding process by categorizing weld joint hardness according to the dilution ratio of a base material and establishing a standard for quantitative evaluation.

Microstructural Characterization and Tensile Behavior of TA1 Titanium Alloy Sheet Welded by Electron Beam Welding

2021 ◽  
Vol 1027 ◽  
pp. 149-154
Author(s):  
Sen Dong Gu ◽  
Ji Peng Zhao ◽  
Rui Jie Ouyang ◽  
Yong Hong Zhang
Keyword(s):  
Titanium Alloy ◽  
Electron Beam ◽  
Fusion Zone ◽  
Heat Affected Zone ◽  
Electron Beam Welding ◽  
Base Material ◽  
Optical Microscope ◽  
Alloy Sheet ◽  
Tensile Behavior ◽  
Electron Backscattered Diffraction

In the present study, TA1 titanium alloy sheets with a thickness of 0.8mm were welded by electron beam welding. Microstructure of the welded region was investigated using optical microscope and electron backscattered diffraction. Then, the tensile test was conducted to analyse the tensile behavior of the welded sheets as well as the fractography of the fracture surfaces. It is shown that the mean grain size in the heat-affected zone is smaller than that in the fusion zone and base material. The strength of the base metal is lower than that of the fusion zone and heat-affected zone. The average values of the yield strength, tensile strength and elongation of the tensile specimens are 224MPa, 335MPa and 35%, respectively. In addition, the tensile specimens of the welded sheets suffer both ductile and brittle deformation during the tensile tests.

scholarly journals Vacuum Brazing of 55 vol.% SiCp/ZL102 Composites Using Micro-Nano Brazing Filler Metal Fabricated by Melt-Spinning

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1470
Author(s):  
Dechao Qiu ◽  
Zeng Gao ◽  
Xianli Ba ◽  
Zhenjiang Wang ◽  
Jitai Niu
Keyword(s):  
Melt Spinning ◽  
Filler Metal ◽  
Aluminum Matrix ◽  
Chemical Properties ◽  
Base Material ◽  
Fracture Morphology ◽  
Aluminum Matrix Composites ◽  
Joint Shear Strength ◽  
Vacuum Brazing ◽  
Sic Particles

The joining methods of Aluminum matrix composites reinforced with SiC particles (SiCp/Al MMCs) are a challenge during the manufacturing process due to the significant differences between SiC particles and base aluminum in terms of both physical and chemical properties. Micro-nano brazing filler metal Al-17.0Cu-8.0Mg fabricated by melt-spinning technology was employed to deal with the joining problem of 55 vol.% SiCp/ZL102 composites in this work. The result indicated that the foil-like brazing filler metal contained uniformed cellular nano grains, with a size less than 200 nm. The solidus and liquidus temperatures of the foil-like brazing filler metal decreased by 4 °C and 7 °C in comparison with the values of the as-cast brazing filler metal due to the nanometer size effect. The maximum joint shear strength of 98.17 MPa achieved with a brazing temperature of 580 °C and holding time of 30 min was applied in vacuum brazing process. The width of the brazing seam became narrower and narrower with increasing brazing temperature owning to the strong interaction between the micro-nano brazing filler metal and 55 vol.% SiCp/ZL102 composites. The fracture morphology of the joint made at a brazing temperature of 580 °C was characterized by quasi-cleavage fracture. After brazing, the chemical concentration gradient between the brazing filler metal and base material disappeared.

Evaluation of the Crack Interaction and Failure Behavior of Components With Crack Fields Using a Damage Mechanical Approach

2019 ◽  
Author(s):  
Christian Swacek ◽  
Patrick Gauder ◽  
Michael Seidenfuss
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Base Material ◽  
Pressure Vessels ◽  
Failure Behavior ◽  
Multiple Cracks ◽  
Critical Crack ◽  
Ongoing Research ◽  
Integrity Assessment ◽  
Crack Tips

Abstract In 2012 non-destructive testing measurements (NDT) of the reactor pressure vessels (RPV) in the Belgian Nuclear Power Plants Doel 3 and Tihange 2 revealed a high quantity of indications in the upper and lower core shells. The most likely explanation is that the measured indications are hydrogen flakes positioned in segregated zones in the base material of the pressure vessels. These hydrogen flakes have a laminar and quasi-laminar orientation with an inclination up to 15° to the pressure retaining surface. Under internal pressure, the crack tips undergo predominantly mixed mode loading conditions, where the induced stress and strain fields of the single crack tips influence each other. The safety assessment of crack afflicted pressurized components is performed by fracture mechanical approaches. For the evaluation of multiple cracks in crack fields, state of the art codes and standards apply interaction criteria and grouping methods, to determine a representative crack, which has to be evaluated. In this paper, the interaction of cracks in crack fields is numerically and experimentally evaluated. Damage mechanical models based on the Rousselier- and the Beremin model are used to investigate numerically the interaction of cracks in crack fields. Experimental data from ferritic flat tensile specimens afflicted with cracks are used to verify the numerical results. The damage mechanical calculations reveal critical crack arrangements due to coalescence behavior and cleavage fracture probability. These results and ongoing research intends the derivation of interaction criteria for cracks in crack fields. The interaction criteria will be used for the definition of a representative flaw for a conservative integrity assessment of crack afflicted components.

A52M/SA502 Dissimilar Metal RPV Repair Weld: Evaluation of Different Techniques

2020 ◽  
Author(s):  
Heikki Keinänen ◽  
Pekka Nevasmaa ◽  
Juha Kuutti ◽  
Caitlin Huotilainen ◽  
Iikka Virkkunen ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Nuclear Power ◽  
Filler Metal ◽  
Post Weld Heat Treatment ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Repair Welding ◽  
Reactor Pressure Vessel Steel ◽  
Nickel Base ◽  
Reactor Pressure

Abstract As part of nuclear power plant ageing management, the increased probability of a need of repair welding must be taken into account along with the increase of plant lifetime. An essential prerequisite for successful and safe repair welding is that the applied welding procedures have been properly validated and qualified prior to their use. For instance, if no post-weld heat treatment can be performed and the desired tempering effect has to be based on temper-bead technique, a user needs to scan among several available repair welding procedures. A decision has to be made which of the procedures provides the maximum desired tempering effect with the case in question. This research is a part of a larger experimental effort developing repair welding techniques, and is a part of the Finnish Nuclear Power Plant Safety Research Programme SAFIR2022. The currently studied experimental repair welding case is a low-alloy steel mock-up with an austenitic cladding. Repair welding is assumed to represent a ‘worst-case’ scenario where a postulated linear crack-like defect exists beneath the cladding and might extend across the interface into the reactor pressure vessel steel side. This postulated defect will be removed by machining, and the thereby machined groove will be filled by repair welding using a nickel-base super alloy 52M filler metal by cold metal transfer-gas metal arc welding with a robotic arm. In this paper, different repair welding techniques and alternatives are shortly surveyed based on existing literature. Overall, published documentation was sparse. While only few studies were considered relevant in terms of established links to actual repair cases of under-cladding defects in reactor pressure vessels, others were mainly for modelling and simulation purposes without e.g. cladding groove preparation or the use of irradiation-embrittled material. Most of these procedures were based on the use of nickel-base alloy filler metal in the combination with temper-bead welding technique, with the aim at omitting both preheating and post-weld heat treatment. The main challenge in the repair weld design is to optimise all relevant welding parameters, including the thermal efficiency of temper-bead welding, in order to obtain a sound, defect-free weld with controlled reactor pressure vessel steel heat affected zone maximum hardness. In the simulations presented in the paper, the goal was to compute the resulting deformations, strains and stresses induced by the repair process and make a-priori estimates of the effectiveness of different repair techniques based on the numerical predictions. The numerical analyses allow the comparison of the procedures and enable selecting the one with most efficient combination of weld thermal cycles in terms of tempering and normalisation effects. The prediction of prevailing residual stresses is also important when further application of the component is considered. The paper is followed by Part II, in which the topics of experimental evaluation and material characterization of the repair weld are presented.

scholarly journals Repairs of Damaged Castings Made of Graphitic Cast Iron by Means of Brazing

2017 ◽  
Vol 17 (3) ◽  
pp. 91-96 ◽  
Author(s):  
M. Mičian ◽  
R. Koňár
Keyword(s):  
Cast Iron ◽  
Visual Inspection ◽  
Filler Metal ◽  
Base Material ◽  
Filler Materials ◽  
Brass Alloy ◽  
Electrical Arc ◽  
Aluminium Bronze ◽  
Ac Current ◽  
Brazed Joints

AbstractThe article summarizes the theoretical knowledge from the field of brazing of graphitic cast iron, especially by means of conventional flame brazing using a filler metal based on CuZn (CuZn40SnSi – brass alloy). The experimental part of the thesis presents the results of performance assessment of brazed joints on other than CuZn basis using silicone (CuSi3Mn1) or aluminium bronze (CuAl10Fe). TIG electrical arc was used as a source of heat to melt these filler materials. The results show satisfactory brazed joints with a CuAl10Fe filler metal, while pre-heating is not necessary, which favours this method greatly while repairing sizeable castings. The technological procedure recommends the use of AC current with an increased frequency and a modified balance between positive and negative electric arc polarity to focus the heat on a filler metal without melting the base material. The suitability of the joint is evaluated on the basis of visual inspection, mechanic and metallographic testing.

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