• Journal of Welding and Joining
• /
• v.23 no.6
• /
• pp.43-48
• /
• 2005

This work was carried out to obtain sound welds and to select a most suitable binary metal joint among three different dissimilar binary metal combinations such as Zr-4/Ta, Mo/Ta and Ti/Ta(seal tube/sensor sheath) joints fur the instrumented nuclear fuel irradiation test. To do this, Taguchi experimental method was employed to optimize the experimental data. In addition, metallography, micro-focus x-ray radiography and hardness test were conducted to examine the welds. From the weld bead appearance, penetration depth and bead width as well as weld defects standpoint, Zr-4/Ta joint is suggested for the circumferential joining between a seal tube and a sensor sheath. The optimized welding parameters based on Zr-4/Ta joint are suggested as well.

• Journal of Industrial Technology
• /
• v.9
• /
• pp.21-28
• /
• 1989

For the study of the fatigue behavior, high-strength bolted connections on a small scale were manufactured, and carried on fatigue tests. Its experimental values were analysed by stress-fatigue life (S-N) curve. Three types of specimens : the base metal, the cireular hole and the welded sperimens had same net section were made. Through the same tests those experimental values were compared with those of the high-strength bolted conneetions. The results of these studies are as followings. It was found that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the high-strength bolted conneetions were much more about 14% and 16% than that of the base metal specimen. It was thought that this trend was due to frictional force increasing fatigue strength. It was known that fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the welded joints were less 29% and 21% than that of base metal specimen. It was thought that that trend was due to weld flaw. It was appeared that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the high-strength bolted connections were much more about 38% and 30% than that of welded joint. It was thought that it was due to both frictional force increasing the fatigue strength in bolted connections and weld flaw decreasing the fatigue strength in welded connections. It was found that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the B3 specimens were much more 2% and -2% than that of the B4 specimen. It was thought that that trend was due to the frictional force, which concerned with shape of specimen. It was known that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the specimen with circular hole was less 61% and 65% than that of base metal. It was known that the allowable stress for bolted joint was higher than that of welded Joints. If that research is continued and more data are accumulated it can be expected that a basic pattern to provided the indicator of the fatigue design of the bolted connections of steel structures and persume the safety and lifeproof of existing structures is given.

• Journal of Welding and Joining
• /
• v.34 no.3
• /
• pp.61-68
• /
• 2016

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 E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

• Journal of the Korean Society of Industry Convergence
• /
• v.14 no.2
• /
• pp.59-65
• /
• 2011

$CO_2$ Welding which uses $CO_2$ instead of inert gas is most widely used in industrial sites. Welding rod for $CO_2$ Welding is roughly divided into solid wire and flux cored wire. $CO_2$ Welding has higher efficiency than any other welding methods, and also economic and speedy to handle, that's why is used frequently for welding general structures. As most of studies about $CO_2$ Welding are focused on metallurgical changes of successful joints, they developed theories about the change of configuration on weld parts. This study is especially focused on not only the change of configuration on weld parts, but also the change of the penetrating depth through changing the position of welding torch. For inspection, applied AWS A5.20 E70-1 among welding wires and fixed moving angles of torch, but controled the values of voltage and the position of welding. Also Automatic Feed Mechanism is used for exact movement of material, specimen is a piece of steel for general structures. By measuring and analyzing the configuration of sliced section and the values of welding leg length and welding throat after welding, the outcome about the changes turned out.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.8 s.251
• /
• pp.931-940
• /
• 2006

Defect assessment of a weld zone is important in fitness-for-service evaluation of plant components. Typically a J and $C^*$ estimation method for a defective homogeneous component is extended to a mismatched component, by incorporating the effect due to the strength mismatch between the weld metal and the base material. The key element is a mismatch limit load. For instance, the R6/R5 procedure employs an equivalent material concept, defined by a mismatch limit load. A premise is that if a proper mismatch limit load solution is available, the same concept can be used for any defect location (either a weld centre defect or a heat affected zone (HAZ) defect) and for any material combination (either two-material or multi-material combinations; either similar or dissimilar joints). However, validation is still limited, and thus a more systematic investigation is needed to generalise the suggestion to any geometry, any defect location and any material combination. This paper describes the effect of structural geometry on the $C^*$ integral for defective similar welds, based on systematic elastic-creep 2-D and 3-D finite element (FE) analyses, to attempt to elucidate the questions given above. It is found that the existing 'equivalent material' concept is valid only for limited cases, although it provides conservative estimates of $C^*$ for most of cases. A modification to the existing equivalent material concept is suggested to improve accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.4 no.3
• /
• pp.19-25
• /
• 1984

In the welded structure, the most dengerous section is welded parts and almost fractures of welded structure occur from welded parts. Accordingly, in other to prevents of fracture, it is important seeking the fracture behavior of welded parts. In this study as basic investigation of fracture behavior of welded parts, it is investigated that local distribution of fracture toughness and effect of multipass electrode welding, also effect of release of residual stress were investigated, as the subjected. material, the used steel having fatigue history and unused steel were selected. As the result of this study, it is dear that the base metal of unused steel and heat affected zone and weld metal are different each other in fracture toughness, and it seems clear that the weld metal may will become source of fracture because of it having the most low fracture toughness. Especially, in the case of crack occur in the used steel, it will be the most brittle section in the structure because of it having low fracture toughness then weld metal. It affirmation that, if welded parts has not flaw, the multi pass electrode welding effective to improve of fracture toughness, also release of residual stress is none effective to improve of fracture toughness in this study.

• Journal of Welding and Joining
• /
• v.28 no.1
• /
• pp.41-46
• /
• 2010

The low alloy-steel material(1.0Cr-0.5Mo, SA213T12), which has widely been used for the waterwall tube in the conventional power plant, do not have enough creep rupture strength for waterwall tubes of the Ultra-supercritical(USC) boilers. According to this reason, the high-strength low alloy-steel(2.25Cr-1.0Mo, SA213T22) has newly been adopted for the waterwall tube in the USC boilers. This paper presents failure analysis on weld-joint of the waterwall tubes in USC boilers. Visual inspections were performed to find out the characteristics of the fracture. Additionally both microscopic characteristics and hardness test were carried out on failed tube samples. Failures seem to happen mainly because the welding process has not been conducted strictly.(preheating, P.W.H.T and so forth). Thus, this paper has the purpose to describe the main cause of the poor welding process and to explain how to prevent similar failures in those weld-joints.

• Journal of Welding and Joining
• /
• v.35 no.3
• /
• pp.68-74
• /
• 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.

• Journal of Korean Society of Steel Construction
• /
• v.23 no.4
• /
• pp.483-491
• /
• 2011

The fabrication of steel structural members always involves welding process such as flux cored arc welding. Therefore, for the application of structural steels to cold regions, it is a prerequisite to clarify the service temperature of the welded joints in order to ensure the structural integrity of the welded parts. In this study, the Charpy impact test was conducted to evaluate the service temperature of structural steel weld. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The service temperatures of the weld metal, HAZ (heat affected zone) and base metal were derived by the absorbed energy and the impact test requirements; thus the applicability of the structural steels to cold regions was discussed in detail.

• Journal of Welding and Joining
• /
• v.11 no.4
• /
• pp.44-56
• /
• 1993

The arc welding processes are substantially nonlinear, in addition to being highly coupled multivariable systems, Frequently, not all the variables affecting the welding quality are known, nor may they be easily quantified. From this point of view, decoupling between the welding parameters from the welding quality is very difficult, which makes it also difficult to control the welding parameters for obtaining the desired welding quality. In this study, a neural network based on the backpropagation algorithm was implemented and adopted for the selection of gas metal arc welding parameters of the fillet joint, that is, welding current, arc voltage and welding speed. The performance of the neural network for modeling the relationship between the welding quality and welding parameters was presented and evaluated by using the actual welding data. To obtain the optimal neural network structure, various types of the neural network structures were tested with the experimental data. It was revealed that the neural network can be effectively adopted to select the appropriate gas metal arc welding parameter of fillet joints for a given weld quality.