입열량에 따른 FCAW용접부 파괴인성에 미치는 미세조직의 영향

신용택,강성원,김명현,Shin, Yong-Taek,Kang, Sung-Won,Kim, Myung-Hyun 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.3

This paper is to evaluate fracture characteristics of API 2W Gr.50 TMCP steel weldment typically applied for offshore structures, with the focus on the influence of heat input arising from flux cored arc welding. Based on the results and insights developed from this study, it is found that the toughness for both CTOD and impact exhibits a tendency to decrease as the weld heat input increases. The reheated zone of weldmetal exhibit lower hardness than solidified zone and microstructure that are liable to affect the toughness are acicular ferrite and martensite-austenite constituents (M-A). In particular, M-A is a more effective micro-phase for CTOD toughness than impact toughness.

Evaluation of Fracture Behavior of the Reheated Weld Zone in API 2W Gr. 50 Steel Weld Metals

신용택,Hae Woo Lee 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.5

In this study the effect of martensite-austenite (M-A) constituents on the fracture behaviour of the reheated weld zone formed by subsequent weld passes in API 2W Gr. 50 steel welds was evaluated. For the weld thermal cycle simulation process with the Geeble thermal simulator, the actual single-pass weldment was used rather than the base metal. The reheated weld zone in the weld metal was categorized into four typical areas according to the peak temperature. The test results indicated that toughness is closely related to the fraction of the martensite-austenite constituents.In particular, the intercritical reheated weld zone with a high fraction of M-A as well as a coarse-grained reheated zone can be considered as local brittle zones of weld metal.

해양플랜트용 YP 690 MPa급강 다층 용접부의 재열 균열 특성 평가

신용택,조영주 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8

This study evaluated the relationship between reheat cracking that occurs in the reheated weld zone formed by subsequent multi-pass welding and the preheat/interpass temperature. The multi-pass weldment was YP 690 MPa high-strength steel, which is used in mobile offshore platform units. The welding process was flux-cored arc welding (FCAW), which coupons were constrained by welding to simulate an actual constraint condition. Three preheat/interpass temperature ranges were employed. The characteristics of the weldment subjected to preheat/interpass temperatures higher than 80°C satisfied the relevant specifications. In the bending testing, a weldment subjected to a preheat/interpass temperature range of 50-60 °C was fractured. The results demonstrated reheat cracking in the reheated weld zone in multi-pass weldments. Reheating cracking (RHC) was initiated at carbides precipitated along the grain boundaries, induced by multipass heating; some cracks were arrested in the reheated zone and the others propagated to the columnar weld metal. The hardness of the cracked specimens was higher than that of the specimen subjected to a higher preheat/interpass temperature, confirming that a susceptible microstructure had formed due to the faster cooling rates. In the analysis of weld residual stress, the specimen with the lower preheating/interpass temperature range showed higher tensile residual stress than that of high preheating/interpass temperature range. Therefore RHC in the reheated zone of the weldment was mainly affected by grain boundary carbides, a higher hardness, and residual stresses. Based on the above discussion, the mechanism of RHC and assessment of structural integrity is presented.

Effects of Heat Input on Pitting Corrosion in Super Duplex Stainless Steel Weld Metals

신용택,Hak soo Shin,Hae Woo Lee 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.6

Due to the difference in reheating effects depending on the heat input of subsequent weld passes, the microstructure of the weld metal varies between acicular type austenite and a mixture of polygonal type and grain boundary mixed austenite. These microstructural changes may affect the corrosion properties of duplex stainless steel welds. This result indicates that the pitting resistance of the weld can be strongly influenced by the morphology of the secondary austenite phase. In particular, the ferrite phase adjacent to the acicular type austenite phase shows a lower Pitting Resistance Equivalent (PRE) value of 25.3, due to its lower chromium and molybdenum contents, whereas the secondary austenite phase maintains a higher PRE value of more than 38. Therefore, it can be inferred that the pitting corrosion is mainly due to the formation of ferrite phase with a much lower PRE value.

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.

TMCP 및 QT강 용접부에 있어 균열길이가 파괴특성에 미치는 영향

신용택(Y.T. Shin),신학수(H.S. Shin),강성원(S.W. Kang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.11

This experimental investigation focuses on an evaluation of fracture characteristics of API 2W Gr.50 (TMCP) and 580 ㎫ class high-strength steel (QT) weldments with respect to crack length to width ratio. Crack Tip Opening Displacement (CTOD) values from Single Edge Notched Bending (SENB) specimen are associated with the Charpy toughness of root weld located at the middle of the specimen thickness and showed lower toughness values according to the increasing crack length to width ratio. In fractography analysis, t. The hardness values of the reheated zone in weld metal are lower than the as solidified zone, and fractures are initiated at the reheated zone with low hardness values within the center third of section thickness.

해양용 UNS S32654강의 기술 개발 현황

신용택(Yong-Taek Shin) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.5

Nickel alloy, especially Alloy 625, is used widely in industrial applications such as aerospace, chemical, petrochemical and marine applications due to their good mechanical properties, excellent fabricability, weldability and good corrosion resistance. Especially, it is obviously applied in FPSO’s moon pool structure and caisson tubular of CPF under seawater environment. Recently, UNS S32654 was developed to substitute alloy 625 because of high cost price. In this study, mechanical properties and corrossive properties of UNS S32654 are reviewed and proposed its applications.

클래드강 적용을 위한 선급용 강재의 열처리 특성 평가

신용택(Yong-Taek Shin) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.5

Clad steel has good corrosion resistance and mechanical properties arising from the hot rolling of dissimilar metals, such as carbon steel and stainless steel. However both good corrosion resistance from the cladding plate material(stainless steel) and mechanical properties from the base plate material (carbon steel) are difficult to obtain because the different steels display opposite behaviors during the cladding process. In order to make clad steel for application in the hulls of ships, proper materials selection and heat-treatment conditions are necessary. In this study, mechanical properties of base plate materials with different chemical composition were evaluated according to heat condition of cladding plate material.

멤브레인형 LNG 탱크용 오스테나이트계 스테인리스강의 저온강도 및 피로강도에 관한 연구

이해우,신용택,박정웅,이재원,강창룡 대한용접접합학회 1999 대한용접·접합학회지 Vol.17 No.3

Feasibility study of the application of a developed annealed austenitic stainless steel at cryogenic temperature has been performed for membrane tank of LNG ship. Chemical properties of developed stainless steel are compared with a domestic commercial stainless steel and a foreign stainless steel which are used for LNG ships. Tensile properties at cryogenic temperature and fatigue strength at room temperature are measured for but and lap joints which are TIG welded specimens. Developed stainless steel having a small amount of titanium component shows the finest grain size in the HAZ, compared with the other stainless steel studied. Tensile strength, elongation and fatigue strength of the developed stainless steel are equal to those of the foreign stainless steel studied and are higher than the domestic commercial stainless steel studied.

예열온도 변화에 따른 레일용접부의 충격인성 및 균열특성

이해우,신용택 ( Hae Woo Lee,Yong Teak Shin ) 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.1

High carbon steel is used for rails due to the excellent wear resistance, however the welding of high carbon steel is more difficult than that of mild steel owing to the high hardenability and sensitivity to cracking at the weldment. In this study, the impact toughness and cracking behavior of a rail weldment were evaluated as function of preheating temperatures. Impact toughness were more excellent in the specimen welded with preheating temperature above 250℃ than that below 100℃, and cracks were not detected in the specimen welded with preheating temperature above 250℃.