Irradiation-induced phases in an Fe ion irradiated CLAM steel

Abstract

CLAM (HEAT-9) steel samples were subjected to a standard heat treatment involving a normalizing for 0.5 h at 980 °C and a tempering for 1.5 h at 760 °C. The standard heat-treated steel samples were irradiated with 3.5 MeV Fe13+ ions at 400 °C to 0.53 dpa and 0.61 dpa. The precipitate phases of standard heat-treated steel samples and the irradiated steel samples were observed and analyzed using transmission electron microscopies and energy dispersive X-ray spectrometers. Through the analyses of selected-area electron diffraction pattern and energy dispersive X-ray data of thin foil specimens, the effects of irradiation on the main inherent precipitate phases, Cr-rich M23C6 and Ta-rich MX, in standard heat-treated steel were investigated, and three kinds of phases induced by the irradiation were found in the irradiated steel. After irradiation, Cr-rich M23C6 and Ta-rich MX phases were observed and confirmed to be still present in the steel, but the Cr/Fe ratio and W content in the Cr-rich M23C6 precipitates decreased obviously. These three irradiation-induced phases in the irradiated steel were identified as Fe-rich M3C carbide with a simple orthorhombic crystal structure, sigma-FeCr intermetallic compound with a body-centered tetragonal crystal structure, and Fe-Cr binary intermetallic compound with a body-centered cubic crystal structure. The identified Fe-rich M3C/sigma-FeCr/Fe-Cr phases have a metal element composition of 92–98Fe and 2–8Cr/85–95Fe and 5–15Cr/40–90Fe and 10–60Cr (in at.%), and a size range of 80–190/60–190/70–300 nm, respectively. The formation of these three irradiation-induced phases in the steel are also discussed.