• Proceedings of the KWS Conference
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• 2008.05a
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• pp.20-20
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• 2008

• Journal of Welding and Joining
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• v.34 no.1
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• pp.35-40
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• 2016

Recent developments of Laser metal 3D deposition with wire feeding are reviewed which provide an alternative to powder feeding method. The wire feeding direction, angle and position as well as laser power, wire feeding rate, and deposition speed are found to be key parameters to make quality deposition with high throughput. When compared with the powder feed, the wire feed shows higher material efficiency, higher deposition rate, and smoother surface. Large elongated columnar grains which have epitaxial growth across deposit layers are observed in deposit cross sections. The growth direction is parallel to the thermal gradient during the deposit process. Tensile properties are found to be dependent on the direction due to the anisotropic deposit property. A real-time feedback control is demonstrated to be effective to improve the deposition stability.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.209-211
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• 2005

Super duplex stainless steels have been used for offshore oil and gas piping systems which are subject to corrosion atmosphere, because they have excellent resistance to Stress Corrosion Cracking (SCC) and Pitting corrosion and high strength/weight ratio. Normally, the welding for duplex stainless steels has been peformed using GTAW with Ar shielding gas. However, in case of using Ar as shielding gas, the corrosion resistance at root weld metal will be deteriorated due to loss of nitrogen from weld deposit during welding. It is wellknown that the corrosion resistance of super duplex stainless can be restored by addition of nitrogen as shielding gas. In this study, we made super duplex welding with using several kinds of shielding and purging gases and investigated the relationship between shielding gas and corrosion resistance. Consequently, it was shown that corrosion resistance of weld deposit can be restored by addition of $N_{2}$ as shielding gas.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.60-67
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• 2014

The ability of electronic packages and assemblies to resist solder joint failure is becoming a growing concern. This paper reports on a study of high speed shear energy of Sn-4.0wt%Ag-0.5wt%Cu (SAC405) solder with different electroless Ni-P thickness, with $HNO_3$ vapor's status, and with various pre-conditions. A high speed shear testing of solder joints was conducted to find a relationship between the thickness of Ni-P deposit and the brittle fracture in electroless Ni-P deposit/SAC405 solder interconnection. A focused ion beam (FIB) was used to polish the cross sections to reveal details of the microstructure of the fractured pad surface with and without $HNO_3$ vapor treatment. A scanning electron microscopy (SEM) and an energy dispersive x-ray analysis (EDS) confirmed that there were three intermetallic compound (IMC) layers at the SAC405 solder joint interface: $(Ni,Cu)_3Sn_4$ layer, $(Ni,Cu)_2SnP$ layer, and $(Ni,Sn)_3P$ layer. The high speed shear energy of SAC405 solder joint with $3{\mu}m$ Ni-P deposit was found to be lower in pre-condition level#2, compared to that of $6{\mu}m$ Ni-P deposit. Results of focused ion beam and energy dispersive x-ray analysis of the fractured pad surfaces support the suggestion that the brittle fracture of $3{\mu}m$ Ni-P deposit is the result of Ni corrosion in the pre-condition level#2 and the $HNO_3$ vapor treatment.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.4
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• pp.770-783
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• 2015

Lately, high production rate welding processes for Al alloys, which are used as LNG FPSO cargo containment system material, have been developed to overcome the limit of installation and high rework rates. In particular, plasma-metal inert gas (MIG) hybrid (PMH) welding can be used to obtain a higher deposition rate and lower porosity, while facilitating a cleaning effect by preheating and post heating the wire and the base metal. However, an asymmetric undercut and a black-colored deposit are created on the surface of PMH weld in Al alloys. For controlling the surface defect formation, the wire feeding speed and nozzle diameter in the PMH weld was investigated through arc phenomena with high-speed imaging and metallurgical analysis.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.141-143
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• 2005

Yttrium has been investigated as hydrogen trapping site in pure iron and HSLA steel welds. Assessment of hydrogen trapping parameters for yttrium oxide has also shown the high potential of yttrium addition to improve hydrogen management in high strength steel welding. The purpose of this study was to reduce and control the diffusible hydrogen content in the weld deposit.

• Journal of Welding and Joining
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• v.31 no.5
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• pp.1-6
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• 2013

In carrying out the elastic-plastic analysis, four conditions (equilibrium equation, constitutive equation, condition of compatibility and yield condition) should be satisfied. In welding, the temperature largely changed from a melting temperature to a room temperature. So, yield stress of materials largely changed, too. In particular, yield stress becomes about zero over $700^{\circ}C$. The analysis should be carried out under the condition that equivalent stress generated in temperature increment ${\Delta}T$ did not exceed yield stress of materials at high temperature over $700^{\circ}C$. It should be sufficiently recognized that the obtained results were not reliable if this condition was not satisfied.

• Proceedings of the KWS Conference
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• 1998.05a
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• pp.150-154
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• 1998

The purpose of this paper is to investigate optimum welding conditions of STS 304 thin sheet by GTA welding and control 6 $\delta$--fenite which is harmful in mechanical processing, corrosion problem and can be formed brittle a phase in using long term at high temperature. One series of automatic welds was made using argon plus 10, 20, 30 % nitrogen to ensure a fully austenite deposit. Results obtained were summarized as follows: 1) 6 $\sigma$ferrite content in the weld metals is influenced largely by the nitrogen content. 2) Additions of nitrogen to the shielding gas can significantly reduce the amount of retained delta ferrite and result in an increase in hot cracking. 3) Bead width was increased when Ar + $N_2$ shielding gas was used and travel speed was increased. 4) Ar+$N_2$ shielding gas made weld metal ductile and reduce 6 -$\delta$-ferrite.

• Journal of Welding and Joining
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• v.18 no.5
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• pp.112-116
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• 2000

The development of new spraying processes has increased the demand for high quality protective coatings. Many thermal spraying processes have been developed to obtain coatings for a wide spectrum of materials and substrates. The plasma spray process was used to deposit coatings of WC-12%Co powders on mild steel substrate, and the characteristics of as-sprayed and vacuum heat treated coatings have been investigated. The variations of microhardness and bond strength in WC-12%Co coatings after heat treatment under vacuum circumstance have been investigated. The effects of phases and morphologies of WC-12%Co coatings have been investigated by utilizing X-ray diffraction and scanning electron microscopy, respectively. The microhardness and bond strength of the coatings were increased with increasing the temperature in the temperature range of $700^{circ}C~1000^{\circ}C$. The bond strength was obtained 49 MPa after vacuum heat treatment at $1000^{\circ}C$.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.355-360
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• 2002

ElectroSlag Strip Overlaying (ESSO) process has been around since 1970. ESSO process had limited acceptance due to a few problems associated with the use of this process in its very early stage. Limited knowledge and, most significantly, poor quality of the equipment and welding flux gave the ESSO process a bad name. However, this process is well accepted today and used in North America, Europe and Japan. The ESSO process provides low dilution overlays at high deposition rates, excellent and consistent deposit chemistry with excellent surface quality, and virtually no defects. Capitan has taken this process one step further through extensive research and development of the process itself as well as the equipment. The improvement brought to the process warranted the issuance in May 2000 of an US patent. This study demonstrates the feasibility of this process with immediate positive production results. The main achievements of this work are as follows: $\textbullet$ Development of six various strip-flux combinations on three different base materials: carbon steel, $\frac{1}{4}$ Cr/.5 Mo and 2 $\frac{1}{4}$ Cr/l Mo, fully tested with: penetrant, ultrasound, bends, hardness, overlay chemistry, corrosion and hydrogen disbonding. $\textbullet$ 12" dia. 90 hot formed elbows from straight pipe electroslag overlayed with "1 layer" and "2 layer" Alloy 625 $\textbullet$ a very unique development of miniaturized overlaying equipment able to perform overlay in pipe with diameters as low as 10" (254 mm). This development has large applications in the field of offshore, petrochemical, refining, pulp and paper and power generation industries. The aftermath of this development was its immediate acceptance by major end users with the completion of four projects of overlayed pipe in the USA and Far East Asia.