Ni-Mo-Cr계 저합금강의 천이온도영역에서의 파괴인성에 미치는 Ni 및 Cr 함량의 영향Effects of Ni and Cr Contents on the Fracture Toughness of Ni-Mo-Cr Low Alloy Steels in the Transition Temperature Region
Materials used for a reactor pressure vessel(RPV) are required high strength and toughness, which
determine the safety margin and life of a reactor. Ni-Mo-Cr low alloy steel shows better mechanical properties
than existing RPV steels due to higher Ni and Cr contents compared to the existing RPV steels. The present
study focuses on effects of Ni, Cr contents on the cleavage fracture toughness of Ni-Mo-Cr low alloy steels
in the transition temperature region. The fracture toughness was characterized by a 3-point bend test of
precracked Charpy V-notch(PCVN) specimens based on ASTM E1921-08. The test results indicated that the
fracture toughness was considerably improved with an increase of Ni and Cr contents. Especially, control of
Cr content was more effective in improving fracture toughness than manipulating Ni content, though Charpy
impact toughness was changed more extensively by adjusting Ni content. These differences between changes
in the fracture toughness and that in the impact toughness were derived from microstructural features, such
as martensite lath size and carbide precipitation behavior.