• Journal of Welding and Joining
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• v.15 no.5
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• pp.84-91
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• 1997

The metal transfer phenomenon of the pulsed-GMAW is simulated by formulating the electromagnetic force incorporated with the Volume of Fluid algorithm. The free surface profiles, pressure and velocity distributions within the drop are computed numerically. Axial velocity and acceleration generated during peak current period are found to have a significant effect on drop detachment. Therefore, the accelerated inertia force becomes one of important factors affecting metal transfer in the pulsed-GMAW. When the pulse current parameters are selected properly, the molten drop is detached just after current pulse, and the operating range of the pulsing frequency increases with higher peak current and duty cycle. Calculated operating ranges show reasonably good agreements with the available experimental data.

• Journal of Welding and Joining
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• v.13 no.1
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• pp.89-102
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• 1995

The evaluation of reheat cracking susceptibility in CrMoV turbine rotor steel was performed using thermally simulated heat affected zones. The examinations were carried out in terms of microstructural characterization, microhardness measurement and a Charpy type notch opening three point bend test. It was found that reheat cracking susceptibility increased as the peak temperature increased. This effect was due to the combined effects of the carbide dissolution and unrestricted grain growth at 1350.deg. C peak temperature. Reheat cracking susceptibility was estimated based on microhardness measurement and prior austenite grain size. It was established that for this particular material, reheat cracking in coarse grained heat affected zone can be eliminated if the microhardness is below about 360DPH and the grain size is below about 30.mu.m. It is evident that reheat cracking susceptibility can be eliminated or reduced by carefully controlling the welding parameters such that a refined structure is produced in the coarse grained heat affected zone.

• Journal of Welding and Joining
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• v.14 no.2
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• pp.46-56
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• 1996

HAZ impact toughness of Ti-oxide steel was investigated and compared to that of a conventional Ti-nitride steel. Toughness variations of each steel with weld peak temperatures and cooling rates were interpreted with microstructural transformation characteristics. In contrast to Ti-nitride steel showing continuous decrease in HAZ toughness with peak temperature, Ti-oxide steel showed increase in HAZ toughness above $1400^{\circ}C$ peak temperature. The HAZ microstructure of the Ti-oxide steel is characterized by the formation of intragranular ferrite plate, which was found to start from Ti-oxide particles dispersed in the matrix of the steel. Large austenite grain size above $1400^{\circ}C$ promoted intragranular ferrite plate formation in Ti-oxide steel while little intragranular ferrite plate was formed in Ti-nitride steel because of dissolution of Ti-nitrides. Ti-oxides in the Ti-oxide steel usually contain MnS and have crystal structures of TiO and/or $Ti_2O_3$.

• Journal of Welding and Joining
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• v.17 no.3
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• pp.55-65
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• 1999

Metallurgical factors influencing toughness of the Intercritically Reheated Coarse-Grained Heat Affected Zone (ICCG HAZ) of multiple welded SA508-cl.3 Reactor Pressure Vessel Steel were evaluated. The recrystallized austenite formed along the prior austenite grain boundaries and late interfaced on heating to the intercritical range was transformed to bainite and/or martensite during cooling. The newly formed martensite always included some retained austenite(M-A constituents). The characteristics(amount, hardness, density, and size) of M-A constituents were found to be strongly associated with both peak temperature and cooling time(△t8/5(2)) of last pass. Toughness in the ICCG HAZ was deteriorated with increasing amount of M-A constituents which was increased with increasing the last peak temperature within the intercritical temperature range. Meanwhile, for the same intercritical peak temperature, toughness was decreased with increasing cooling time. When cooling time was short, the dominant factor influencing toughness of the ICCG HAZ was amount of M-A constituents. However, when cooling time was lengthened, the hardness difference between M-A constituents and softened matrix(tempered martensite) was found to be the dominant factor.

• Journal of Welding and Joining
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• v.31 no.2
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• pp.57-62
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• 2013

Magnesium has good castability and limited workability, so its products have been manufactured by almost casting processes. In this study, a pulsed Nd:YAG laser was used to butt-weld the sand casting magnesium alloys. And the effect of welding conditions such as peak power, pulse width, welding speed was evaluated in detail. As a result of this study, large underfill and plenty of spatter taken place under the conditions with high peak power. Thus, it is recommended to use low peak power and long pulse width to obtain good welds with deep penetration. It is also confirmed that the welding speed and pps(pulse per second) are directly connected at weld defects such as underfill, porosity.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.59-67
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• 2016

The automotive manufactures increase their use of lightweight materials to improve fuel economy and energy usage has a significant influence on the choice of developing materials. To meet this requirements manufacturers are replacing individual body parts with lightweight metals, for these the process treating and painting surfaces is changing. The pre-coated steels are newly developed to avoid the conventional complex and non-environmental painting process in the body-in-white car manufacturing. The development of new joining techniques is critically needed for pre-coated steel sheets, which are electrically non-conductive materials. In the present study, dissimilar combination of pre-coated steel and galvanized steel sheets were joined by the self-piercing rivet, adhesive bonding and hybrid joining techniques. The tensile shear test and free falling high speed crash test were conducted to evaluate the mechanical properties of the joints. The highest tensile peak load with large deformation was observed for the hybrid joining process which has attained 48% higher than the self-piercing rivet. Moreover, the hybrid and adhesive joints were observed better strain energy compared to self-piercing rivet. The fractography analyses were revealed that the mixed mode of cohesive and interfacial fracture for both the hybrid and adhesive bonding joints.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.55-61
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• 2016

Recently developed ferritic heat resistance steel, T24 was used to evaluate microstructure characteristics of simulated heat affected zone. Also, correlation between the prior austenite grain size and amount of $M_{23}C_6$ carbide dissolution was discussed. With the increasing of peak temperature, Grain size steadily increased up to $1050^{\circ}C$ and then rapidly increased at $1150^{\circ}C$. Of the peak temperature $950{\sim}1050^{\circ}C$, amounts of $M_{23}C_6$carbide dissolution are low. But Most of $M_{23}C_6$ carbide that is inhibited grain growth were dissolved above $1050^{\circ}C$ and decreased volume fraction of carbide. This indicates that grain growth may be achieved through dissolution of carbide in the base material. As of welding, due to very rapid heating rate, $M_{23}C_6$ carbide exists above equilibrium solution temperature that is $800^{\circ}C$, even at $1050^{\circ}C$. So, It was confirmed that close correlation between carbide dissolution in the base material and grain growth. Calculated grain size has a linear relationship with peak temperature, on the other hand, measured grain size discontinuously increased between $950{\sim}1050^{\circ}C$ and above $1050^{\circ}C$. Grain size of heat affected zone at $1350^{\circ}C$ peak temperature showed maximum 67um and minimum 4um. Also, The number of side showed 3 to 10.

• Journal of Conservation Science
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• v.35 no.1
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• pp.11-18
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• 2019

The adhesives joining Buddhist scripture scrolls from medieval Korea(Goryeo Dynasty, A.D. 918~1392) are different from wheat starch adhesive. The composition of the adhesive was analyzed using Attenuated Total Reflectance-Fourier Transform Infrared(ATR-FTIR) spectroscopy. In the adhesive used to join Buddhist scripture scrolls, peaks attributed to amide I and amide II of the protein and carbohydrate were detected in the ATR-FTIR spectra, and no carbonyl peak($1745cm^{-1}$) for oil was detected in the 2nd derivative ATR-FTIR spectra. The ATR-FTIR spectra almost coincided with those of defatted soybean powder adhesive. Hence, the adhesives joining Buddhist scripture scrolls were inferred to be soybean adhesive prepared from a defatted soybean cake.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.70-74
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• 2014

On this study, we researched the in-process monitoring during fiber laser welding as well as on the first paper. On the previous/formal study, we analyzed the change of emission signal on thin plate welding. On this study, however, we analyzed RMS and FFT with emission signals in laser welding on lap joint and butt joint of 8mm-thick 316L stainless steel. As the result, the movement of specific frequency peak was observed according to welding speed changes. Furthermore, frequency peak as a result of FFT on the thick plate welding are much clearer than on the thin plate welding. Therefore, it is expected that the welding parameter changes can be predicted in case of applying FFT to in-process monitoring.

• Journal of Welding and Joining
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• v.27 no.3
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• pp.67-72
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• 2009

The flux cored arc welding (FCAW) process is one of the most frequently employed and important welding process due to high productivity and excellent workability. The process is performed either as an automated process or as a semi-automatic process. In FCAW process, welding voltage has been considered as a qualitative indication of arc length. But it is necessary to let welding operators know, maintain and manage the arc length directly by estimating and displaying it. In this study, to develop arc length estimation technique, we measured a welding circuit resistance($R_sc$) and then we calculated welding circuit voltage drop($V_sc$). Also, we measured arc peak voltage($V_ap$). By subtracting $V_sc$ from $V_arc$, we can easily calculate net arc voltage drop($V_arc$). Consequently, we suggested arc length estimating equation and basic algorithm by regressive analyzing the relationship between net arc voltage drop($V_arc$) and real arc length(Larc) measured by high speed camera. Therefore, arc length can be predicted by just monitoring welding current and voltage.