Present status of development of high chromium steel for Japanese FBR components

This paper presents the establishment of the provisional specifications and material strength standard of the high chromium (Cr) steels for fast breeder reactor (FBR) components. For the improvement of toughness and ductility of the steels, a series of mechanical tests and metallurgical examinations are performed for several kinds of high Cr steels with the controlled balance of tungsten (W) and molybdenum (Mo). In addition, the effect of heat treatment condition on material properties is also investigated. Based on these results, it is revealed that W should be diminished to achieve better ductility and toughness and that it is difficult to improve the long-term properties by changing heat treatment condition. Then the provisional specifications of the high Cr steel for FBR components are given and the provisional material strength standard is proposed for the specifications of the steel. The standard obtained in this study is utilized for the FBR plant design.