Japan Atomic Energy Research Institute (JAERI) has developed large superconducting magnets and cryogenic structural materials to construct the International Thermonuclear Experimental Reactor (ITER). Material rules in structural design code like ASME Boiler and Pressure Vessel Code is required to construct the ITER or commercial fusion facilities in rational way. From this point of view, it is important to predict the strength at cryogenic temperatures of nitrogen strengthened austenitic stainless steels based on the strength at room temperature. Tensile tests were performed at room temperature, in liquid nitrogen (77K), in liquid helium (4K), and in gaseous helium (about every 50 degrees between 7K and 227K). Empirical prediction quadratic curves in taking account of carbon and nitrogen (C+N) effect on strength were established for JJ1 and 316LN based on the test results. It is expected that cryogenic strength of commercial base materials can be predicted by using these curves.
