한국가스학회:학술대회논문집

The Korean Institute of GAS (한국가스학회)
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Evaluation of Fracture Toughness of Heat-Affected Zone in $9\%$ Ni Steel for Inner Wall of LNG Storage Tank

LNG 탱크 내조용 $9\%$ Ni 강 열영향부의 파괴인성 평가

  • Jang J. I. (Division of Materials Science and Engineering, Seoul National University) ;
  • Yang Y. C. (Research and Development Center, Korean Gas Corporation) ;
  • Kim W. S. (Research and Development Center, Korean Gas Corporation) ;
  • Hong S. H. (Research and Development Center, Korean Gas Corporation) ;
  • Kwon D. (Division of Materials Science and Engineering, Seoul National University)
  • Published : 1997.09.01
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Abstract

The objective of this study is, with concept of fitness-for-purpose, to evaluate the fracture toughness in X-grooved weld HAZ(heat-affected zone) of QLT(quenching, lamellarizing and tempering)-processed $9\%$ Ni steel, qualitatively and quantitatively, and analyze the relation with the change of microstructure. In general, CTOD test is widely used to determine the fracture toughness of steel weldments. But several problem of accuracy has been brought up. Therefore, in this study, modified CTOD test was used for X-grooved weld HAZ for $9\%$ Ni steel. Additionally, microstructure of HAZ is observed and analyzed by OM, SEM and XRD. From the resulty, HAZ toughness of QLT-$9\%$ Ni steel decreased as the evaluated region approaches the fusion line. The decreased toughness was partly caused by reduction of the retained austenite content, resulted from decreased nucleation site of the retained austenite content, resulted from decreased nucleasion site for reverse transformation due to the increasing fraction of coarse grained region. On the other hand, unexpectedly, the increasing fraction of ductile weld did not increase the HAZ toughness. Therefore, in this X-grooved weld HAZ, the primary factor affecting fracture toughness was the fraction of coarse grained region, i.e., the weakest region.

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