Consideration of Strength Difference between Welded Joint and Base Metal in Mod. 9Cr-1Mo Steel for High Temperature Structural Design

The mod. 9Cr -1 Mo steel is a candidate material for the main components of the fast reactor, and its design allowable stress is specified in Japan Society of Mechanical Engineers fast reactor standard. The reactor will be larger in size. For the design, welding is also required at a part to be a high-temperature and high-stress. Therefore, allowable stress for the weld joint is required. When the weld joint of the mod. 9Cr -1 Mo steel is used for a long time under high temperature, creep damage of the fine grain region in the heat affected zone remarkably progresses. The strength of the weld joint is lower than that of the base metal. Therefore, the allowable stress of the weld joint must be considered such a strength reduction. In this paper, by comparing the strength properties of mod. 9Cr-1Mo steel base metal and weld joint, allowable stress for weld joint by reduction of base metal strength in the restriction of primary stress of JSME fast reactor standard was examined.