In order to reduce radiation exposure in nuclear plants (ABWR), Co free wear resistant alloys for rollers in FMCRD (Fine Motion Control Rod Drive) were investigated. Microstructures of conventional Ni-base alloy (WPM) and Co-base alloy were compared to get hints for improving the wear resistance of Ni-base alloys, and a developing conception, dispersing large size Cr carbides into soft Ni matrix, was obtained. The conception was confirmed to be valid by sintered Ni alloys. And then, cast Ni alloys in which less material defect could be expected than sintered Ni alloys were prepared to examine the wear and impact properties. It was known that 1.92.1C-30Cr-Ni(mass%) cast alloys showed much higher wear resistance than those of WPM and Co-base Alloy in high temperature water of 288°C, and that the absorbed energy in sharpy impact test of the cast Ni alloys was more than two times larger than those of WPM and Co-Alloy 3.
