Low-cycle fatigue of developmental Ni-Cr-W alloys in simulated VHTR environment

Strain-controlled low-cycle fatigue tests were conducted on new developmental alloys at 9000C in the simulated VHTR helium environment. Among several candidates two materials i.e. KSN (Ni-16Cr-26W) and SSS113MA (Ni-23Cr-18W) tested were selected as the heat performing alloys for application to the intermediate heat exchanger tubes by Ministry of International Trade and Industry - Agency of Industrial Science and Technology - Nuclear Steelmaking program (1973 -- 1980). The program is known as the ERANS program, i.e. Engineering Research Association of Nuclear Steelmaking. Based on the obtained results the following conclusions are drawn; 1) Low-cycle fatigue life of SSS113MA was about 50% longer than that of KSN in impure helium. 2) The ratios of Nsub(f) in impure helium to Nsub(f) in 1--3 x 10-6 Pa vacuum were 0.1 -- 0.2 for both materials. 3) The fracture mode was almost purely intergranular in both materials. 4) The levels of low-cycle fatigue strength shown by KSN and SSS113MA were substantially lower than those of the data band for the existing heat-resistant alloys in the similar temperature range. (author)