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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.
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.
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℃.
Nb 첨가량에 따른 436 페라이트계 스테인리스강 용접부의 미세조직 변화 및 공식 저항성에 관한 연구
김종민 ( Jong Min Kim ),신용택 ( Yong Taek Shin ),이상화 ( Sang Hwa Lee ),이준희 ( Jun Hee Lee ),이성룡 ( Sung Riong Lee ),김순호 ( Soon Ho Kim ),이해우 ( Hae Woo Lee ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.12
This paper identified the effects of Nb on microstructure. Also, it has studied on uniform and pitting corrosion resistance in a ferritic stainless steel weld metal of the automobile exhaust system. We fabricated 3 flux cored wires designed with 0-1.0 wt% Nb and performed Flux Cored Arc Welding. We observed the microstructure with the SEM/EDS and EBSD. To evaluate the uniform and pitting corrosion resistance, we performed a potentiodynamic polarization test in 0.2 M H2SO4 and 0.1, 0.3, 0.5 M NaCl. As a result of the tests, we found that as the amount of addition of Nb rose, the amount of Cr-carbide fell. The microstructure became more refined. The specimen with 1.0%Nb added had the highest uniform and pitting corrosion resistance. After the pitting corrosion test, a pit was formed at the grain boundary that has no addition of Nb. In addition, in the specimen with added Nb, pits were formed at the inclusions.
자동차 배기계용 AISI 409L 페라이트계 스테인리스강 용접부 물성에 관한 연구
이상화 ( Sang Hwa Lee ),신용택 ( Yong Taek Shin ),이해우 ( Hae Woo Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.4
In this study, we prepared a sample of AISI 409L weld metals using automotive exhaust manifolds and evaluated their corrosion properties by conducting an anodic polarization test after 10 minute of heat treatment at 900℃. The specimens of AISI 409L transformed fully ferrite. Weld metal was refined more than base metal. Specimen of heat treatment at 900℃ and as weld specimen was formed precipitation. However heat treatment specimen was bulkly formed and coarser than the as weld specimen. The strength measured by 10 Hv highly at heat treatment specimens in comparison with as weld. The increase in strength is attributed to the precipitation of Ti. The result of heat treatment suggest that there was a decrease of current density and high corrosion potential. Following heat treatment process produced Ti precipitation and for this reason, it can restrain Cr-carbide so that steel will have more corrosion resistance.
해양 구조물용 강재 FCAW 용접부의 파괴인성 특성에 관한 연구
강성원,김명현,김용빈,신용택,이해우,Kang Sung-Won,Kim Myung-Hyun,Kim Yong-Bin,Shin Yong-Taek,Lee Hae-Woo 대한용접접합학회 2004 대한용접·접합학회지 Vol.22 No.6
Fracture toughness is an important parameter in designing offshore structures to ensure resistance to fracture at various temperatures. In this study, a series of experiments is carried out to obtain fracture toughness values (CTOD) of API 2W Gr.50B, welded using FCAW(Flux Cored Arc Weld). In particular, a comparison of absorbed impact energy and CTOD values are made with respect to two different welding groove shapes; double-V-groove and double-bevel-groove. Charpy impact tests are performed for specimens sampled near the root gap, and CTOD tests are carried out for three point bending specimens having the notch at weld zone. While Charpy impact test result is determined to be a good qualitative measure of fracture toughness, no quantitative correspondence between impact absorbed energy and CTOD values was found. Based on the experiment, it is observed that double-V-groove welds give lower transition temperature than those of double-bevel-groove.
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.