• Journal of Welding and Joining
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• v.26 no.5
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• pp.66-73
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• 2008

Welding work in pre-erection or erection stage of shipbuilding construction to be carried out in flat and vertical upward position mostly and Electrogas welding(EGW) is actively applied especially for vertical butt joint of thicker steel plate recently. In this study considered how to develope and improve mechanical properties of weld metal and HAZ in high heat input welding processes such as EGW and Electroslag welding(ESW) with its welding equipment in order to extend the application range to the longitudinal members and hatch coaming parts of container ship. Some components of welding system and parameters were modified to get the faster travel speed and reduce weld heat input, and also by adding additional filler rods or tubes increase the amount of deposited weld metal. With the test get some good date can apply to actual fabrication work and recommend items to manufacture welding materials make better. Above all things it's a fruition that to prepare the possibility of application of ESW to shipbuilding construction which fill up the gap of stoppage days of more than 20 years.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.16-21
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• 2016

Recent keywords of the heavy industries are large-scale structure and productivity. Especially, the sizes of the commercial vessels and the offshore structures have been gradually increased to deliver goods and explore or produce oil and natural gas in the Arctic. High heat input welding processes such as electro gas welding (EGW) have been widely used for welding thick steel plates with flux-cored arc welding (FCAW), especially in the shipbuilding industries. Because high heat input welding may cause the detrimental effects on the fracture toughness of the welded joint and the heat affected zone, it is essential to obtain the sufficient toughness of welded joint. There are well known that the fracture toughness like CTOD, CVN, and KIC were very important factors in order to secure the safety of the structures. Furthermore, the welding residual stress should be considered to estimate the unstable fracture in both EGW and FCAW. However, there are no references on the welding residual stress distribution of EGW and FCAW with thick steel plates. Therefore the welding residual stresses were very important elements to evaluate the safety of the welded structure. Based on the measurement results, the characteristics of residual stress distribution through thickness were compared between one-pass electron gas welding and multi-pass flux-cored arc welding. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress of EGW is tensile on both surfaces and compressive at the inside of the plate. The magnitude of residual stresses by electron gas welding is lower than that by flux-cored arc welding.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.63-68
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• 2008

This paper has aimed to prevent excessive heat input by controlling arc distribution and heat input capacity with pulse GTAW in order to improve weld quality in 0.08mm pressure gauge diaphragm and flange welding parts. A design of experiment was designed using Box-Behnken method to optimize a welding process. The pulse GTAW parameters such as pulse current, base current, pulse duty, frequency and welding speed were set to input variables while hydraulic pressure that represents welding characteristics in diaphragm and flange joint were set to output variables. Based on the test result, a second regression equation was obtained between input and output variables and turned out significant. Besides, an influence of parameters has been confirmed through response surface analysis using the second-order regression equation and optimum welding condition was obtained through a grid-search method. The optimum welding condition was set to pulse current 84.4(A), base current 29.6(A), pulse duty 58.8(%), frequency 10(%), and welding speed 596(mm/min). Then, decent bead shape was acquired with no excessive heat input under the $2.3kgf/cm^2$ of hydrostatic pressure.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.165-167
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• 2005

Compared with Inconel 625 (ERNiCrMo-3) weld, Nb-free Alloy 59 (ERNiCrMo-13) weld with 15% Mo showed much higher resistance to hot cracking. Especially in the condition of current 350A and 30CPM of welding speed, no crack was detected at Inconel 625 fillet weld. Furthermore, it was found that the strength of Alloy 59 is sensitive to welding heat input. Up to around 14kJ/cm of heat input, Alloy 59 showed 678N/$mm^{2}$ of ultimate strength and 466N/$mm^{2}$ of yield strength. However, as heat input increased above 14kJ/cm, Alloy 59 weld could not satisfy the weld strength required for European LNG tank.

• Journal of Welding and Joining
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• v.26 no.1
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• pp.69-75
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• 2008

Spot welding which use the main process for side block production of stainless steel railway vehicle is legged behind in laser welding about a quality and productivity. Although the laser welding has many potential advantages such as low heat input and aspect ratio of weld bead, its application to a new structural component still is required many engineering data including mechanical properties such as tensile, fatigue strength, etc on. Therefore, experimental analysis was carried out to understand the fatigue phenomena of different thickness stainless steel overlap joining panels by Nd:YAG laser welding. The fatigue life curves were obtained through fatigue tests with the various levels of applied load. The fatigue life is related with the parameters such as gap size and penetration depth through experiment. As the results, tensile strength and fatigue life were proportional in heat input level and gap was identified the major factor for fatigue life. Also we could know that deferent a-ferrite content at HAZ depend on welding heat input was important factor to determine a formation of initial crack and total fatigue life cycle.

• Journal of Welding and Joining
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• v.32 no.1
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• pp.6-14
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• 2014

This paper has an aim to evaluate microstructure and fracture toughness of TMCP steel weldment applied for off-shore wind tower with the focus on the effect of heat input on the weldment with various welding processes; FCAW(13kJ/cm and 30kJ/cm), SAW(62kJ/cm), and EGW(177kJ/cm). Based on experimental results developed from this study, it was found that the impact toughness of top side for TMCP steel weldments with heat input up to 62 kJ/cm satisfied the required minimum value except the EGW(177kJ/cm). The heat input and microstructure are the main factors of impact toughness. The heat input of 13kJ/cm on back side with low heat input increased the amount of grain boundary ferrite which has low impact toughness, and heat input of 177kJ/cm on top side is significant enough to produce the austenite grain growth. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by OM and EDS. As the heat input increased, the inclusions also grew and a nucleation site decreased. The size of nonmetallic inclusions and the crack width was nearly similar, therefore the inclusions were related with the crack propagation.

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.201-203
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• 2000

In this study, effect of welding parameters on the defect density in the weldments produced by high frequency electric resistance welding process. The defect density measured by X-ray radiography showed a W-type curve as a function of heat input rate. The mechanisms of the such behavior were discussed based on the chemical compositions of the oxides formed at the weldments.

• Journal of Welding and Joining
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• v.21 no.7
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• pp.42-48
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• 2003

Welding distortion is a current issue in many industrial parts, especially for heavy industry such as shipbuilding, plant industry. The welding process has many processing parameters influencing welding angular distortion such as heat input power, welding speed, gas flow rate, plate thickness and the welded material properties, etc. In this work, the conventional local minimization concept was applied to find a set of optimum welding process parameters, consisted of welding speed, plate thickness and heat input, for a minimum angular distortion. An analytic solution for welding angular distortion, which is based on laminated plate theory, was also applied to investigate and optimize the welding process parameters. The optimized process parameters and the angular distortion for various parametric conditions could be easily found by using the local minimum concept.

• Journal of Welding and Joining
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• v.33 no.1
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• pp.41-48
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• 2015

In this study, the effect of heat input on weld metal microstructure and the effects of dissimilar weld heat affected zone in quenched and tempered ASTM A517 on the stainless steel AISI 316L is investigated through the optimization of welding parameters. For this purpose, two welding techniques are used, tungsten-conventional gas and pulsed gas with weld wire ER 309MoL with Diameter 2.4 mm. Research showed that the grain size of the heat affected zone in pulsed welding is less compared with conventional welding; weld metal structure is fully austenitic, it has a finer structure in the pulsed method. Additionally, the growth of weld metal adjacent steel A517 is different from steel 316L. Further, investigation showed that the rate of dilution is less in the pulsed method and the impact energy is increased in each three regions of the weld metal and heat affected zones in the pulsed method; the fracture in the weld metal and heat affected zone of steel 316L is quite soft and it is semi-crispy in the heat affected zone of steel A517.

• Laser Solutions
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• v.3 no.2
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• pp.53-61
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• 2000

On the laser weld production line, a slight alteration of the welding condition produces many defects. The defects are monitored in real time, in order to prevent continuous occurrence of defects, reduce the loss of material, and guarantee good quality. The measurement system is produced by using three photo-diodes for detection of the plasma and spatter signal in CO$_2$ laser welding. For high speed CO$_2$ laser welding, laser tailored welded blanks for example, on-line weld quality monitoring system was developed by using fuzzy multi-feature pattern recognition. Weld qualities were classified optimal heat input, a little low heat input, low heat input, and focus misalignment, and final weld quality were classified good and bad.