고변형능 라인파이프강의 미세조직과 기계적 특성에 미치는 압연 및냉각 조건의 영향

Effects of rolling and cooling conditions on microstructures and mechanical properties of high-deformablepipeline steels were investigated in this study. Six kinds of pipeline steels were fabricated by varying rollingand cooling conditions, and their microstructures were analyzed by scanning electron microscopy, electron backscattereddiffraction, and transmission electron microscopy. Tensile and Charpy impact tests were conducted onthe steels in order to examine the mechanical properties. The steels rolled in the two-phase region showed betterlow-temperature toughness than those in the single-phase region due to the larger amount of ferrites havinghigh-angle boundaries, although they have lower strength and absorbed energy. The steel rolled in single-phaseand finish-cooled at higher temperature showed a good combination of high strength and good low-temperaturetoughness as well as excellent deformability of the lowest yield ratio and the highest uniform elongation becauseof the presence of fine ferrite and a mixture of various low-temperature transformation phases.