• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1817-1825
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• 2000

The purpose of this study is to examine the fracture toughness of the welded pipe from the viewpoint of FATT for the S38 and S42 steels used widely as the pipe material. Post weld heat treatment(PW HT) was carried out like following conditions: temperature of 67$0^{\circ}C$, I hour of holding time and cooling in furnace. Fracture toughness was obtained by measuring the crack opening displacement(COD) of the notched specimens over the range of temperature from -14$0^{\circ}C$ to -$25^{\circ}C$. Hardness values at fusion line near around were the highest and the microstructures at welded zone were coarsened. Regardless of the pipe materials, COD and temperature curves of the as-welds were moved toward higher temperature compared with those of the parents. However, COD and temperature curves of the PWHT specimens were positioned at lower temperature compared with those of the as-welds. The more heat input causes to decrease the COD values at the constant temperature. It was verified through the recrystallization treatment that PWHT was attributed to move toward lower temperature region considerably due to the improved plastic deformation at the same applied COD value of 0.3mm and softening effect. In case of the weldment of S38 steel, cleavage fracture was observed at -105$^{\circ}C$ unlike the structural steels, in which brittle fracture mode was generally shown at - 196$^{\circ}C$.

• Journal of Welding and Joining
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• v.26 no.6
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• pp.81-91
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• 2008

The weldability of resistance spot welding of TRIP1180 steels for automobile components investigated enhance in order to achieve understanding of weld fracture during tensile-shear strength (TSS) test. The main failure modes for spot welds of TRIP1180 steels were nugget pullout and interfacial fracture. The peak load to cause a weld interfacial failure was found to be related to fracture toughness of the weld and the weld diameter. Although interfacial fracture occurred in the spot welded samples, the load-carrying capacity of the weld was high and not significantly affected by the fracture mode. Substantial part of the weld exhibits the characteristic dimple (or elongated dimple) fractures on interfacial fractured surface also, dimple fracture areas were drawmatically increased with heat input which is propotional to the applied weld current. In spite of the high hardness values associated with the martensite microstructures due to high cooling rate. The high load-carrying ability of the weld is directly associated with the area of ductile fracture occurred in weld. Therefore, the judgment of the quality of resistance spot welds in TRIP1180 steels, the load-carrying capacity of the weld should be considered as an important factor than fracture mode.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.672-682
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• 2008

The resistance spot welding of TRIP590 steels was investigated to enhance understanding of weld fracture during tensile-shear strength (TSS) test. The main failure modes for spot welds of TRIP590 steels were nugget pullout and interfacial fracture. The peak load to cause a weld interfacial failure was found to be related to fracture toughness of the weld and the weld diameter. Although interfacial fracture occurred in the samples, the load carrying capacity of the weld was high and not significantly affected by the fracture mode. Substantial part of the weld exhibits the characteristic dimple (or elongated dimple) fractures on interfacial fractured surface, in spite of the high hardness values associated with the martensite microstructures. The high load-bearing ability of the weld is directly associated with the area of ductile fracture occurred in weld. Therefore, the judgment of the quality of resistance spot welds in TRIP590 steels, the load carrying capacity of the weld should be considered as an important factor than fracture mode.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.65-73
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• 2011

Microstructural characteristics of two high strength (600 MPa & 800 MPa) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 MPa grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 MPa and 800MPa grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was $0.7{\mu}m$. The 800 MPa grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 MPa grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 MPa grade weld metal.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.365-369
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• 2004

Recently, Inconel 625 is used widely in offshore processing piping in order to extend the maintenance tenn and improve the quality of anti-corrosion. According to the resistance to attack in various corrosive media at temperatures from $200^{\circ}C$ to aver $1090^{\circ}C$, in combination with good low- and high-temperature mechanical strength. In general, High quality weldments for this material are readily produced by commonly used processes. in recent years, the flux cored arc welding(FCAW) process is becoming more popular due to higher deposition rate and a better weld quality as compared to the shielded metal arc welding (SMAW) process, at the same time, exhibiting equally good weld metal toughness similar to the SAW process. In this study, the weldability and weldment characteristics(mechanical properties and corrosive environment) of Inconel 625 are considered in FCAW weld associated with the several weld shielding gases($80\%Ar\;+\;20\%\;CO_2,\;50\%Ar\;+\;50\%\;CO_2,\;100\%\;CO_2$) in viewpoint of welding productivity.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.8-14
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• 2021

Even welds that have passed non-destructive testing in the case of brittle crack arrest steel materials will actually have very fine weld defects. Based on studies showing that these defects adversely affect the structure if subjected to a certain period of load, the following conclusions were obtained by conducting CTOD tests on welding joints of high-strength BCA materials, structures comprising the upper decks of a large container vessel. First of all, the fatigue pre-cracking in the weld metal and heat affected areas was tested and the behavior was identified. Both parts of the welding joint are allowable range for the class regulations. In addition, CTOD results showed that the CTOD value in the heat affected area was more than 0.5 times higher than in the weld metal area.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.25-32
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• 1999

The objective of this paper is to evaluate the fracture resistance characteristics of SA508 CL.1a carbon steel, TP347 stainless steel and their associated welds manufactured for primary coolant system of Ulchin 3,4 nuclear power plants. The effect of various parameters such as pipe size, welding method, chemical composition, crack plane orientation, metallography and fractography on the material properties were discussed. Test results showed that the effect of pipe size on fracture toughness is negligible while the effect of welding method on fracture toughness is significant. In addition, the drop of fracture toughness in the field fabrication weld of TP347 stainless steel is probably due to the large amount of $\sigma$-phase precipitated on the $\delta$-ferrite boundary and the large size dimples.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.136-137
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• 2004

석유나 가스 등의 자원을 안정적으로 수송하기 위하여 사용하는 라인 파이프는 그 사용 환경에 따라서 다양한 소재 특성을 필요로 하며, 한랭지역에서 사용되는 경우에는 낮은 온도에서도 충분한 인성을 유지할 수 있는 높은 인성을 요구하고 있다. (중략)

• Proceedings of the KWS Conference
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• 2003.05a
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• pp.75-77
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• 2003