Proceedings of the KWS Conference (대한용접접합학회:학술대회논문집)
The Korean Welding and Joining Society
- Semi Annual
Domain
- Materials > Casting/Welding/Joining
2003.05a
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Generally, the Quality of a weld joint is strongly influenced by process parameters during the welding process. In order to achieve high quality welds, mathematical models that can predict the bead geometry to accomplish the desired mechanical properties of the weldment should be developed. To achieve this objectives, a sensitivity analysis has been conducted and compared the relative impact of three process parameters on bead geometry in order to verify the measurement errors on the values of the uncertainty in estimated parameters. The results obtained show that developed mathematical models can be applied to estimate the effectiveness of process parameters for a given bead geometry, and a change of process parameters affects the bead width and bead height more strongly than penetration relatively.
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The evaluation of HAZ toughness and cold crack susceptibility of 90mm thickness API 2W Grade 50 steel has been made in accordance with API RP 2Z as preproduction qualification test to be certified as il steel supplier from Shell International E & P. It was shown that the steel has superior HAZ toughness; CTOD value for CGHAZ more than 1.5mm at -10
$^{\circ}C$ , CVN absorbed energy more than 150J at -60$^{\circ}C$ . Additionally, no generation of cold cracks was observed at 0.7kJ/mm even without preheating condition. These excellent results are due to the extremely low hardenability in HAZ of the steel. -
Lee, Chung-Rae;Kim, Sung-Wook;Choi, Woo-Hyuk;Eom, Sang-Ho;Lee, Chang-Hee;Kim, Jae-Chul;Choi, Chul 40
In general, nickel-base superalloy has been extensively used as land-based gas turbine blades and vanes. Plasma transferred arc welding(PTAW) has been considered as a repair welding process of nickel-base superalloy. This research evaluated the relationship between hot ductility behavior and hot cracking susceptibility in nickel-base superalloys. Ductility recovery rate of nickel base superalloys was found to be poor due to incipient melting and constitutional liquation. This seems to increase the hot cracking susceptibility. -
The empirical model for predicting the prior austenite grain size in low-alloy steel weld HAZ was developed through examining the effect of alloying element. The test alloys were made by vacuum induction melting. Grain growth behaviors were observed and analyzed by isothermal grain growth test and subsequent metallography. As a result, it was found that the grain growth might be controlled by grain boundary diffusion and the empirical model for grain growth was presented.
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No Abstract, See Full Text
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The potential advantages of the hybrid welding process are improved weld penetration, enhanced gap tolerance, control of weld metal composition, and improved weld quality in comparison to laser or arc welding. Especially, the deep penetration of hybrid welding is very attractive in welding of thick plates. In this study, therefore, the influence of arc power in hybrid welding on detailed bead dimensions at different laser power levels was investigated.
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The laser welding and its analysis of thin-sheet carbon steels were carried out with high power CO
$_2$ 1aser. Bead on plate welding of thin sheet was examined to investigate the effect of weld variables of laser welding, and to obtain optimum welding condition. Butt-welding was also carried out to show the effect of gap on the laser weldability of thin sheet. At high welding speed, the partial penetration was obtained by low heat input. Otherwise, porosity was formed in the bead at low weld speed because of too many heat input. The maximum gap tolerance on laser welding was observed to be about 0.2mm. This gap size has good relationship with beam size of laser spot(about 0.3mm). The formability of welded sheet was about 80% value of base metal and the gap size has not affected on the formability, although weld quality is dependent on the gap size. -
The yield strengths of austenitic stainless steel have been approximately doubled by increasing the nitrogen content. But, the increasing the nitrogen cause of increase the pressure of metal vapor inside the keyhole in electron beam welding. During welding, eruptions of keyhole often occur that cause excessive spatter, concavity, and porocity in the weld zone. Additionally the fast evaporation of nitrogen content cause of decrease the strength of weld zone. Therefore in this paper, we investigated of the weldability of electron beam welding and the change of chemical content after welding for strengthened austenitic stainless steel, measured the deformation scale of both of electron beam and narrow gap TIG and the spike fluctuation in the root.
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This study deals with the resistance spot welding of aluminized steels. According to the test results it was clear that the weldability of aluminized steels was equivalent to or better than that of Zn coated steel. Microstructural inspection revealed that molten aluminum that was repelled from the weld during the process, piled up at the split zone. The test results also demonstrated that the weld metal of aluminized steels could hardly produce the weld crack even higher welding heat Input was applied.
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Laser weldability of aluminized steels of 0.8mm thick has been investigated. Test materials were cut from the commercial steels that were produced at the Coating Mill of POCOS. Test coupons for welding were prepared by using a conventional shearing machine and no additional edge treatment was peformed. Nd:YAG laser welding system was mainly applied to make weld specimens. Test results revealed that almost no spattering was observed even though the welding was peformed with no overlap joint clearance. Bead quality of aluminized steel laser weld was smooth and stable. According to x-ray inspection results, it was proved that the laser welds of aluminized steels were metallurgically defect free.
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The existing heating unit is indirect-heating method that make use or the nichrome wire or halogen lamp. The indirect-heating method has the demerits of long warming time, high power consumption and many organization parts. In this study, the heating unit of direct-heating method manufactured as being the thermal spray coating of conductive heating material on the surface of heating unit in order to improve the demerits of indirect-heating method. And YSZ added Ni-20Cr that had moderate electrical resistivity was chosen of the conductive heating material.
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The multi function sprayed coating is used for direct-heating, wear resistance and high bonding strength. The merits of surface direct-heating coatings are short warming time, low power consumption and better wear resistance that can be used in many organization parts. In this study, the surface direct-heating and wear resistance can be improved by spraying the proper materials on the surface
$Al_2$ O$_3$ 40%TiO$_2$ powder and Ni-20%Cr powder that had the properties of conduction and high wear resistivity are used in order to improve wear resistance, electrical properties and bonding strength. -
Power plant efficiency and availability depend greatly on condenser performance. However, during commissioning of Yeonggwang #1/2 steam condenser sodium leakage occurred, because of tube to tubesheet only roll expanding. Therefore this report is explaining that pre-test for the shake of improvement reliable repair processes & selected sampling tube re-expansion in-situ applications.
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This paper introduces a new automatic welding equipment for offshore pipeline construction. This paper also describes the design technology and functions of the automatic welding equipment, which features the reliability of the equipment.
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This paper describes the control system which was designed and implemented for a new automatic welding equipment. The system has the self diagnostic function which facilitates maintenance and repairs, and also has the network function via which the welding task data call be transmitted and the welding process data can be monitored.
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The purpose of research is to measure power and dynamic resistance value through RMS module. Specially designed RMS-DC hardware module was tested. Its output which is obtained every half cycle was compared with that of commercial weld checker. The results show good agreement and the relative error in the measurement was found to be around 5%.
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The development of lightweight car bodies is the most prominent issue in the automotive industry today, in preparation of environmental regulations such as reduction of CO
$_2$ emissions. Also, with the recent implementation of mandatory off-set collision test, many studies have been carried out to enhance the safety of automobiles. Recently, TRIP(Transformation Induced Plasticity) steel has developed as a prominent alternative due to its high strength and superior elongation. In this study, TRIP steel weldability is evaluated with lobe curve, continuous spot welds, shunt effect, and weld of edge position. -
Orbital GTA welding is used in the pressure pipe line of auto-mobile, LNG and plant piping. To weld the pipe line safely, to some extent, the back bead must be formed in the root pass. In the plate welding the back bead can be observed, but in the pipe welding, the back bead can not be observed directly. In the welding around circumference, the parameters such as gravity, surface tension and arc force are different at each position. And then D/B for welding condition at each position are required. We also studied about the setting of the optimum orbital welding condition by controlling heat input.
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A genetic algorithm was applied to an arc welding process to determine near optimal settings of welding process parameters which produce good weld quality. It has an advantage of being able to find optimal conditions with a fewer number of experiments than conventional full factorial design. According to the conventional full factorial design, in order to find the optimal welding conditions, 16,384 experiments must be performed. The genetic algorithm however, found the near optimal welding conditions from less than 60 experiments.
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The weld zone of dissimilar formed Al alloy exhibited the complex structure of the two materials and mainly composed of the retreating side material. The mechanical properties were also depended on the dominant microstructure of the weld zone with welding conditions. The different mechanical properties of weld zone with welding conditions were related to the behavior of the precipitates of wrought Al alloy and Si particles of cast Al alloy. The higher mechanical properties of weld were acquired when relatively harder material, wrought Al alloy, was fixed at the retreating side.
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Micro-structure and shear properties with reflow conditions, reflow temperature and time, for In-48Sn solder on BGA package were examined at the temperature between 140 and 170
$^{\circ}C$ for 10 to 3600sec. With increasing reflow temperature and time, the thickness of intermetallic compound formed between solder and pad increased. Shear test indicated shear force increased in the range to a critical value of reflow time, and decreased over a critical reflow time. With increasing reflow temperature and time, the crater occurred on fracture surface because of a increase of crater by voids and IMC particles precipitated in solder. -
Kim, Sung-Wook;Choi, Woo-Hyuk;Wu, Jingwei;Lee, Chung-Rae;Choi, Chul;Kim, Jae-Chul;Lee, Chang-Hee 201
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Ti/Steel 클래드 판재를 제조하기 위하여 티타늄과 강판을 직접 접합하는 경우 접합 계면에 취성이 강한 금속간화합물 및 TiC 탄화물이 발생하여 계면접합강도를 저하시키는 단점이 있다. 이러한 단점을 보완하기 위하여 본 연구에서는 티타늄과 강판 사이에 니켈 박판을 삽입한 후 1223-1323K 온도구간에서 접합 실험하였다. 특히, 온도의 변화에 따라 티타늄과 강판의 계면에 발생되는 금속간화합물의 종류 및 반응층의 크기 변화에 따른 기계적 특성을 조사하였다.
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Finite element analysis of welding processes, which entail phase evolution, heat transfer and deformation, is considered in this paper. Attention focuses on numerical implementation of the thermo-elastic-plastic constitutive equation proposed by Leblond et al in consideration of the transformation plasticity. Based upon the multiplicative decomposition of deformation gradient, hyperelastic formulation is employed for efficient numerical integration, and the algorithmic consistent moduli for elastic-plastic deformations including transformation plasticity are obtained in the closed form. The convergence behavior of the present implementation is demonstrated via a couple of numerical example.
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In this paper thermal stress analysis was done about thin plate during welding. In order to calculate the stresses of welded plates, finite element method was used. And results were compared with previous researches.
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A fracture mechanics analysis methodology for stress corrosion cracks (SCCs) existing in the Alloy 600 nozzle weld joint for control rod drive mechanisms (CRDMs) of pressurized water reactor is studied. Effects of weld residual stresses on the sub-critical crack behavior during the reactor operation are investigated by a fracture mechanics analysis, which is combined with the finite element alternating method. It is found that effects f the residual stresses on the stress intensity factor (SIF) and crack growth rate (CGR) are dominant and values of SIF and CGR of cracks in the region of weld joint are increased by a factor of three or more on an average.
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The longitudinal thermosonic bonding method is investigated in this work for its application to the soldering process for electronic packaging. The effect of the ultrasonic is analyzed through lumped modeling, and the material properties of a viscoelastic model are measured experimentally. The thermosonic bonding method is verified by inserting the Cu pin and Au bump into solder block. As the solder thickness decreases, temperature of the solder is calculated to increase rapidly because of larger strain. Localized heating due to ultrasonic vibration is observed to melt the solder near the pin, which is adequate to the high density electronic package and Pb-free solder having high melting temperature.
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Recently, lots of joining methods of thin metal sheets are being developed in order to improve joint quality and productivity in manufacturing area. Current existing welding methods are continuously challenged as new materials and smaller thickness of metal sheets are required. In this study, laser plug brazing process was investigated as a new joining method of thin metal sheets. A CO2 laser system with automatic feeding of filler metal wire and flux was developed, and laser plug brazing experiments were conducted. The brazed joints were analyzed using various methods.
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Sulfide Stress Corrosion Cracking(SSCC) of welded Steel pipe has been investigated. A specimens are stressed into the synthetic sea water saturated with H
$_2$ S. Therefore SSCC occur at the hardnest point. we are discusses the test methods used for laboratory corrosion testing of welded steel pipe and the results of test. -
In this study, high temperature tensile properties of high tensile strength steels(POSTEN60, POSTEN80) were investigated by elevated temperature tensile test. According toe the results, high temperature tensile strength of POSTEN60 deteriorated slowly to 100
$^{\circ}C$ . As the temperature went up the tensile strength became better because of blue shortness and it deteriorated radically after reached to the maximum value around 300$^{\circ}C$ . For the POSTEN80, high temperature tensile strength deteriorated slowly to 200$^{\circ}C$ .As the temperature went up the tensile strength became better and it deteriorated slowly to 600$^{\circ}C$ after reached to the maximum value around 300$^{\circ}C$ . Strain of high tensile strength steels at the elevated temperature increased radically after the mercury rose to 600$^{\circ}C$ . The strain hardening ratio of POSTEN60 was larger then that of POSTEN80 at the elevated temperature as in the case at the room temperature and it became smaller radically after the mercury rose to 400$^{\circ}C$ . -
The transverse crack, a type of cold crack, occurs perpendicular to the axis of the weld interface, longitudinal residual stresses (
$\sigma$ k direction) are more important in transverse crack occurrence from my own experience. Specimens were fabricated and welded under actual construction conditions, and then residual stresses of longitudinal stresses were measured for different welding conditions with SAW and FCAW process. The residual stress values for the specimen welded Interpass temperature below 30$^{\circ}C$ was higher than the specimen welded interpass temperature of 100~120$^{\circ}C$ . And also the residual stress values for a specimen measured at weld surface, as welded condition, was higher than that of longitudinal residual stresses that was measured from a small test piece, due to the residual stress was relieved in the process of the cutting and machining. Transverse weld cracks were detected in the area of the maximum residual stresses both SAW and FCAW process. -
Residual stresses, which can be produced during the manufacturing process, play an important role in an industrial field. Residual stresses of structures by welding process are exerting negative effect on the fatigue behavior and safety of structure. Results from the elasto-plastic finite element analysis of the welds for a nuclear component, the residual stress distribution after welding. In this study, a finite element technique is developed to simulate the relaxation of the residual stresses due to the mechanical loads of welds.
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A simplified analysis method is proposed in this paper, through which the deformation due to spot welding is obtained. In order to analyze the spot welding process, the finite elements are axisymmetrically modeled, and the results from them are used for analyzing the deformation of spot welded structure. It takes more little time in this simplified analysis than the analysis by 3-D continuum elements, and this analysis produces the results that nearly agree with the measured data.
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