API 2W Gr. 50강의 다층 FCA 용접재의 피로 균열 발생 및 전파 특성에 관한 연구

Abstract

Abstract

Recently, there are many demand of Flux Core Arc Welding (FCAW) in thick plate of offshore structural construction and heavy ship yard. Also there are much severe than past because of the offshore conditions. The structure is bigger and the installing location is dipper in ocean. Hence, very severe safety and strong structure is required against the environment. Most of fatigue crack is initiated at manufacturing stage of welding. During manufacture, many factors are considered for fatigue crack such as material, welding parameter and post welding treatment. For practical application, it is necessary to understand the fatigue crack initiation and propagation of the welded structures. In this paper, experimental fatigue crack initiation and propagation tests were performed on ASTM standard CT specimens for multi path FCA welded API 2W Gr. 50 weldments with 60mm thickness. With other study, it has done more NDE (Non Destructive Examination) such as MT (Magnetic particle Test) and RT(Radiography Test). For the welding, the most of common practice was done on the specimen such as pre-heating and heat input. Also mechanical tests were done after all NDE. Tensile test and Vickers hardness were done on each portions (heat affect zone, weld metal and base metal). Five of CT (Compact Test) specimens were taken on each portions. All the fatigue crack initiation and propagation tests were evaluated and compared to the three different portions, heat affect zone, weld metal and base metal. Consequently, the main results obtained from this investigation reveal that the mean fatigue crack initiation life of the HAZ specimen is the highest among the parent, weld metal and HAZ. And also the coefficient of variation is the highest in weld metal specimen. The variability of short fatigue crack growth rate from notch tip in weld metal and HAZ specimens is higher than parent.