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이수호(Sooho Lee),이영호(Youngho Lee),이영석(Youngseog Lee) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Vertical type radiant tube is being used in Continuous Annealing Line (CAL) as a heat source. High temperature combustion gases are flow through the inside of the radiant tube and released. Hence a certain amount of internal pressure is always in the inside of the radiant tube. Since the radiant tube is generally exposed to high temperature (600~900 ℃) for long time (3~4 years), it is subjected to creep deformation. This study examined variations in creep life of the radiant tube when the internal pressure changes from 0.01㎫ to 0.2㎫. The radiant tube was made of Inconel 601 and Larson-Miller parameter was used to predict the creep life of the radiant tube. Results show that creep life at each region in the radiant tube is sensitive to the internal pressures. In overall, the creep life varied non-linearly as the internal pressure changed.
양조예,이영석,Yang, Zhaorui,Lee, Youngseog 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.1
Evaluation of fracture toughness of welded structures has a significant influence on the structural design. However the residual stresses is redistributed while the welded structures is cut for preparing specimens. This study investigated an effect of the welding residual stress redistribution on the impact absorption energy of Charpy specimen. SA516Gr70 steel plate by at the flux cored arc welding (FCAW) and gas tungsten arc welding(GTAW) was cutting. Specimens for Charpy impact testing were taken from the welded plate. Two material removal mechanisms (wire cutting and water jet) were used to make the specimens. Welding residual stress and redistribution residual stress were measured using the XRD (X-Ray Diffraction) method. The amount of redistribution of residual stress depends on the different material removal mechanism. Redistribution of residual stress of reduced the impact absorption energy by 15%.
공형압연 공정에서 소재 표면흠 발생억제를 위한 패스 스케줄 설계
나두현(Doo Hyun Na),이영석(Youngseog Lee) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.10
본 연구에서는 소재 표면흠 발생을 억제하기 위해 유한요소법을 사용하여 세아베스틸 선재 조압연 라인 공정을 모사하였다. 선재 조업연 라인의 2 번 공형을 설계하였고 이 공형을 압연 라인에 적용하였다. 또한 유한요소법을 사용하여 3 번, 4 번 공형 롤 갭이 변경된 새로운 패스 스케줄을 제안하였다. 본 연구에서는 전단응력비에 의존적인 전단파괴 모델을 사용하였고 소재의 손상된 요소 수를 비교하였다. 손상된 요소는 표면흠을 의미한다. 결과적으로 2 번 공형이 변경된 후 불량률은 이전 공형보다 1.43% 감소되었다. 그리고 새로운 패스 스케줄의 손상된 요소 수는 현재 패스 스케줄보다 37.6% 감소되었다. We simulated the roughing train of the rod mill of SEAH BESTEEL Inc. using finite element method to inhibit surface cracks initiation on workpiece. We designed 2nd pass (square roll) and applied to this roll in the roughing train of the rod mill. Also, we proposed new pass schedule, which changed roll gap of 3rd and 4th groove by using finite element method. We used shear damage model, which is dependent on shear stress ratio and compared the number of damaged elements on workpiece. A damaged element means surface crack. Consequently, after 2nd pass (square roll) is changed, the error rate decreased by 1.43% when compare to that of the old groove. And the number of damaged elements in the new pass schedule decreased by 37.6%, which is less than present pass schedule.