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용접 재료 개발 단계에서 ECA 기법을 통한 재료의 인성 적합성 평가
신용택(Yong-Taek Shin),조영주(Young-Ju Jo),서대곤(Dae-Gon Seo) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.6
Needs for structural integrity procedure such as BS 7910, the nuclear industry document R6 Rev.4 and the European FITNET procedure are being increased in industry. Especially, BS 7910 allows metallic structures to be assessed on the basis of fracture mechanics analysis rather than strict adherence to design and fabricated codes. This study is to propose the flaw assessment to judge the toughness level of welding consumables at the development stage. The FCA welding consumables with YP 690MPa and CTOD over 0.25 mm have been developed and its allowable weld flaw size considering actually applied environment has been evaluated. Since the estimated allowable defect size is sufficiently detectable in nondestructive testing, the toughness of the developed material is judged to be appropriate and no problem in securing the structural integrity.
항복강도 690MPa급 전자세용 FCA 용접와이어 개발에 있어 용접 입열의 영향 평가
조영주(Young-Ju Jo),서대곤(Dae-Gon Seo),신용택(Yong-Taek Shin) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.6
YP 690MPa grade steels are used as the main structural steel for offshore structure such as Jack-up Rig and WTIV(Wind Turbine Installation Vessel). Most of welding consumables applied to YP 690MPa grade steels are basic type flux cored wires that shows the poor weldability and not suitable for all position welding. For this reason, welding consumables with rutile type flux system is required. Rutile type flux cored wires show excellent weldability and apply to all position welding. This paper presents the mechanical properties of weld metal with rutile type flux cored wire developed and finally assessed the possibility for application.
용접 홈 형상에 따른 샤르피 충격 시험 기반 마스터 선도 접근법의 검증에 관한 연구
이진호(Jin-Ho Lee),신용택(Young-Taek Shin),김명현(Myung-Hyun Kim) 대한용접·접합학회 2019 대한용접·접합학회지 Vol.37 No.6
Engineering critical assessment (ECA) is used as a procedure to evaluate the integrity of an engineering structure with flaws. To this end, ECA requires reliable fracture toughness values such as J-integral and CTOD. Ideal fracture toughness data can be obtained from an engineering structure, but may be impossible depending on the operating conditions. Appendix J of the BS 7910 provides a procedure for estimating fracture toughness values from appropriate Charpy impact test data. However, the correlation between Charpy impact energy and fracture toughness is highly conservative because they are not based on a theoretical background. In this regard, the revised BS 7910:2019 provides improved fracture toughness values by applying the yield strength and the Charpy upper shelf energy. The target of this study was to validate the master curve approach in the revised BS 7910 for groove shapes and the sample locations of impact tests. For that purpose, the master curves were compared in terms of the reference temperature obtained from Charpy impact energy data according to BS 7910:2013 and the modified BS 7910:2019. The revised master curve approach resulted in less conservative fracture toughness values. However, there were cases where BS 7910 and modified BS 7910 overestimated the fracture toughness compared to values using CTOD data. Further study of the master curve approach is needed, considering various heat inputs, groove shapes, and welding processes.
Cr(eq)/Ni(eq)비에 따른 AISI 304L 및 AISI 316L 스테인리스강 용접부의 미세조직 및 전기화학적 양극분극 평가
김연희 ( Yeon Hee Kim ),장아영 ( Ah Young Jang ),강동훈 ( Dong Hoon Kang ),고대은 ( Dae Eun Ko ),신용택 ( Yong Taek Shin ),이해우 ( Hae Woo Lee ) 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.12
This pitting corrosion study of welded joints of austenitic stainless steels (AISI 304L and 316L) has addressed the differentiating solidification mode using three newly introduced filler wires with a flux-cored arc welding process (FCAW). The delta ferrite (δ-ferrite) content in the welded metals increased with an increasing equivalent weight ratio of chromium/nickel (Cr(eq)/Ni(eq)). Ductility dip cracking (DDC) was observed in the welded metal containing ferrite with none of AISI 304L and 0.1% of AISI 316L. The potentiodynamic anodic polarization results revealed that the Cr(eq)/Ni(eq) ratio in a 3.5% NaCl solution didn`t much affect the pitting potential (E(pit)). The AISI 316L welded metals with a-ferrite content of over 10% had a superior E(pit) value. Though the AISI 316L welded metal with 0.1% ferrite had larger molybdenum contents than AISI 304L specimens, it showed a similar Epit value because the concentration of chloride ions and the corrosion product induced severe damage near the DDC.
슈퍼오스테나이트계 스테인리스강 GTA 용접부의 용접 적층 및 입열에 따른 공식 부식 특성
고대환(Dae-Hwan Ko),박영일(Young-Il. Park),신용택(Yong-Taek Shin) 대한용접·접합학회 2020 대한용접·접합학회지 Vol.38 No.6
This study investigated the corrosion characteristics of weldments on superaustenitic stainless steels for various heat inputs and numbers of welding passes during gas tungsten arc welding(GTAW). The heat input was changed to 0.7 or 1.4 kJ/mm and the weldment microstructure and chemical composition were analyzed. The weldment corrosion resistance was evaluated by potentiodynamic polarization, and the critical pitting temperature (CPT) was determined. The CPT dropped from 85 to 55 ℃ with both increasing heat input and number of welding passes. The microstructural and chemical compositional analyses revealed that the Mo segregated and precipitated in the interdendritic region, and that the Mo content in the dendritic core was lower than that in the surrounding area. The Mo content decreased when the pitting corrosion initiated. The precipitate content and dendrite core size both increased, and the pitting corrosion resistance decreased with both increasing heat input and number of welding passes.