• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.3
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• pp.19-25
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• 1984

In the welded structure, the most dengerous section is welded parts and almost fractures of welded structure occur from welded parts. Accordingly, in other to prevents of fracture, it is important seeking the fracture behavior of welded parts. In this study as basic investigation of fracture behavior of welded parts, it is investigated that local distribution of fracture toughness and effect of multipass electrode welding, also effect of release of residual stress were investigated, as the subjected. material, the used steel having fatigue history and unused steel were selected. As the result of this study, it is dear that the base metal of unused steel and heat affected zone and weld metal are different each other in fracture toughness, and it seems clear that the weld metal may will become source of fracture because of it having the most low fracture toughness. Especially, in the case of crack occur in the used steel, it will be the most brittle section in the structure because of it having low fracture toughness then weld metal. It affirmation that, if welded parts has not flaw, the multi pass electrode welding effective to improve of fracture toughness, also release of residual stress is none effective to improve of fracture toughness in this study.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.197-199
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• 2004

용접성은 모재의 조직과 기계적 성질 및 Bond 부와 열영향부의 조직과 기계적 성질의 관계로 평가된다. 탈소 함량이 높은 레일강의 경우 용접을 하고 나면 열영향부에 마르텐사이트와 같은 취약조직을 형성하여 경도 값이 높아지고 인성이 저하되어 균열발생 가능성이 높아진다. (중략)

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.231-233
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• 1998

• Proceedings of the KWS Conference
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• 1999.05a
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• pp.282-284
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• 1999

• Proceedings of the KWS Conference
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• 1993.10a
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• pp.61-63
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• 1993

• Journal of Ocean Engineering and Technology
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• v.9 no.1
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• pp.151-160
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• 1995

The characteristics of low temperature impact toughness and stress corrosion resistance at boiling MgCl$_2$ solution of GTA and SMA weld of duplex stainless steels have been investigated. The impact toughness was highest at the GTAW weld metal and lowest at the SMAW weld, which was almost the same as that of the SMAW heat-affected zone. This was attributable to influence of austenite-ferrite phase balance, and the degree and nature of precipitation that occurred during welding. The SCC resistance of the weldments was slightly higher than that of the base metal, whereas no difference in the SCC resistance was found between two different weldments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.528-536
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• 2002

As one step for the safety performance of LNG storage tank, the change in fracture toughness within the X-grooved weld heat-affected zone (HAZ) of newly developed 9% Ni steel, which was submerged arc (SA)-welded, was investigated. Both crack initiation fracture toughness and crack arrest fracture toughness were evaluated by the crack tip opening displacement (CTOD) tests and compact crack arrest (CCA) tests. As the evaluated region approached the fusion line, each test result shorted different tendency, that is, crack initiation toughness decreased while crack arrest toughness increased. The results were discussed through the observation of the microstructural change.

• Korean Journal of Materials Research
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• v.6 no.12
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• pp.1221-1232
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• 1996

용접부 인성을 향상시키기 위해 Ti 산화물을 첨가한 Ti 산화물강에 대하여 용접시 최고가 열온도와 냉각속도의 변화가 용접열영향부의 미세조직에 미치는 영향을 조사하였다. 용접열영향부의 인성향상에 기여하는 acicular ferrite는 140$0^{\circ}C$ 이상의 최고가열온도와 $\Delta$t800-500가 40초보다 빠른 냉각속도에서 활발해 생성되었다. 오스테나이트 결정립내에서 개재물로부터 핵생성된 일차 acicular ferite의 생성량은 전체 aicular ferrite의 약 20% 정도로 적었으며 대부분의 acicular ferrite는 일차 acicular ferrite로부터 생성된 이차 acicular ferrite인 것으로 나타났다. 이차 acicular ferrite는 plate사이에 Fe3C층이 존재하는 것으로 보아 확산기구에 의해 생성되는 것으로 생각된다. 개재물은 TiO, TiO2, TiN, MnS, AI2O3 MnO(galaxite)등으로 구성된 복합상이었으며 개재물이 일차 acicular ferrite의 핵생성 site로 작용하기 위해서는 약 1$\mu\textrm{m}$이상의 크기가 효과적인 것으로 나타났다. Ti 산화물과 TiN는 직접적인 acicular ferrite의 핵생성 site로 작용하기보다는 MnS, galaxite 등의 석출 site로 작용하여 개재물의 크기를 증가시킴으로써 acicular ferrite의 생성을 촉진시키는 것으로 생각된다.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.693-700
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• 2012

In this study, the Charpy impact test along with metallurgical observation was conducted to evaluate low temperature impact toughness of structural steel welds with different welding processes to find out the optimal welding process to guarantee the required impact toughness at low temperatures. The welding processes employed are shield metal arc welding (SMAW) and flux cored arc welding(FCAW), which are commonly used welding methods in construction. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. To investigate the impact toughness at low temperatures of the steel welds, specimens were extracted from the weld metal and the heat affected zone. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The low temperature impact performance was evaluated based on the correlation between the absorbed energy and the microstructure. Analysis of the results showed that the optimal welding process to ensure the higher low temperature impact toughness of the HAZ and the weld metal is SMAW process using the welding consumable for steels targeted to low temperature use.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.67-72
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• 2010

The fracture toughness for the LBB analysis of piping is generally determined by the J-integral according to ASTM E1820. However, since this evaluates a base metal, the fracture toughness for narrow gap welding can be differently than the real value. This study evaluated the plastic  factor of the narrow gap welding part of a nuclear piping with SA508 Cl.1a and SA312 TP316. Also, it performed the fracture toughness test for the narrow gap welding part and applied the new plastic $\eta$ factor equation by Huh, et al. and then compared the results with those according with the ASTM standard.