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용접 열영향부 미세조직 및 재질 예측 모델링 : III. 석출물 - Free 저합금강의 초기 오스테나이트 결정립크기의 영향을 고려한 용접 열영향부 오스테나이트 결정립성장 예측 모델
엄상호,문준오,정홍철,이종봉,이창희,Uhm, Sang-Ho,Moon, Joon-Oh,Jeong, Hong-Chul,Lee, Jong-Bong,Lee, Chang-Hee 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.4
The austenite grain growth model in low alloyed steel HAZ without precipitates was proposed by analyzing isothermal grain growth behavior. Steels used in this study were designed to investigate the effect of alloying elements. Meanwhile, a systematic procedure was proposed to prevent inappropriate neglect of initial grain size (D0) and misreading both time exponent and activation energy for isothermal grain growth. It was found that the time exponent was almost constant, irrespectively of temperature and alloying elements, and activation energy increased with the addition of alloying elements. From quantification of the effect of alloying elements on the activation energy, an isothermal grain growth model was presented. Finally, combining with the additivity rule, the austenite grain size in the CGHAZ was predicted.
API X70 후육강관 SAW용접부 미세조직 및 인성 거동에 대한 연구
엄상호,김성욱,김종현,이창희,김광수,Uhm Sang-Ho,Kim Sung-Wook,Kim Jong-Hyun,Lee Chang-Hee,Kim Gwang-Soo 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.2
API(American Petroleum Institute) steel, as a line pipe material, requires the enhanced mechanical and chemical properties with the environmental severity. Especially, the weld part(weld metal and heat affected zone) is an important region for the safety. However, the study for the behavior of microstructure and toughness in multi-pass welding is seldom. In this study, the relationship between the microstructure and toughness of welds with several welding, bending and heat-treatment conditions was examined. In particular, HIC property in the weld metal was evaluated. The microstructure and toughness in multi-passed HAZ seemed to be determined by the final welding thermal cycle and the low toughness was attributed to the MA constituents formed in the intercritically reheated region. The weld metal showed very low toughness and it was not improved by the change in bending and heat treatment conditions. Additionally, the cracks are observed in the weld metal. from these results, it was found that the choice of welding wire/flux is very important.
페라이트계 스테인리스강 GTA 용접부 특성에 미치는 보호가스 중 산소의 영향
이원배,엄상호,우인수,Lee, Won-Bae,Uhm, Sang-Ho,Woo, In-Su 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.5
The properties of GTA weld for ferritic stainless steel have been studied with different $O_2$ contents in Ar shielding gas at the constant welding speed. A small amount of $O_2$ (0.01~1.0%) was mixed in Ar shielding gas in order to improve the weld penetration. The fully penetrated GTA weld was acquired at 160A weld current shielded by pure Ar gas. Addition of oxygen larger than 0.1% made a full penetration at lower weld current than 160A. The small addition of $O_2$ in Ar shielding gas improved the penetration properties of GTA weld because the $O_2$ in the molten pool accelerated the flow of molten pool and changed the flow pattern from outward to inward direction. The impact energy and DBTT (Ductile- Brittle- Transition-Temperature) of the GTA weld shielded by Ar+$O_2$ (less 0.3%) was similar and the corrosion properties of GTA weld was slightly inferior to those of GTA weld shielded by pure Ar gas.
유종근,문준오,이창희,엄상호,이종봉,장웅성,Ryu, Jong-Geun,Moon, Joon-Oh,Lee, Chang-Hee,Uhm, Sang-Ho,Lee, Jong-Bong,Chang, Woong-Sung 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.1
Considering ferrite grain size in the base metal, the prediction model for $A_{c3}$ temperature and prior austenite grain size at just above $A_{c3}$ temperature was proposed. In order to predict $A_{c3}$ temperature, the Avrami equation was modified with the variation of ferrite grain size, and its kinetic parameters were measured from non-isothermal data during continuous heating. From calculation using a proposed model, $A_{c3}$ temperatures increased with increasing ferrite grain size and heating rate. Meanwhile, by converting the phase transformation kinetic model that predicts the ferrite grain size from austenite grain size during cooling, a prediction model for prior austenite grain size at just above the $A_{c3}$ temperature during heating was developed.
Al-Si 용융도금된 11%Cr 페라이트 스테인리스강, STS409L GTA 용접부의 미세조직과 경도
박태준,공종판,나혜성,강정윤,엄상호,김정길,우인수,이종섭,Park, Tae-Jun,Kong, Jong-Pan,Na, Hye-Sung,Kang, Chung-Yun,Uhm, Sang-Ho,Kim, Jeong-Kil,Woo, In-Su,Lee, Jong-Sub 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.3
Ferritic stainless steels, which have relatively small thermal expansion coefficient and excellent corrosion resistance, are increasingly being used in vehicle manufacturing, in order to increase the lifetime of exhaust manifold parts. But, there are limits on use because of the problem related to cosmetic resistance, corrosions of condensation and high temperature salt etc. So, Aluminum-coated stainless steel instead of ferritic stainless steel are utilized in these parts due to the improved properties. In this investigation, Al-8wt% Si alloy coated 409L ferritic stainless steel was used as the base metal during Gas Tungsten Arc(GTA) welding. The effects of coated layer on the microstructure and hardness were investigated. Full penetration was obtained, when the welding current was higher than 90A and the welding speed was lower than 0.52m/min. Grain size was the largest in fusion zone and decreased from near HAZ to base metal. As welding speed increased, grain size of fusion zone decreased, and there was no big change in HAZ. Hardness had a peak value in the fusion zone and decreased from the bond line to the base metal. The highest hardness in the fusion zone resulted from the fine re-precipitation of the coarse TiN and Ti(C, N) existed in the base metal during melting and solidification process and the presence of fine $Al_2O_3$ and $SiO_2$ formed by the migration of the elements, Al and Si, from the melted coating layer into the fusion zone.