Control of precipitation behavior in reduced activation steels by intermediate heat treatment

► MX precipitates instead of M23C6 during intermediate treatment at 850 °C. ► The volume fraction of M23C6 decreases due to the decrease of carbon content in the matrix during tempering. ► The decrease of volume fraction of M23C6 causes the decrease of the mean size of M23C6 from 150 nm to 70 nm. ► The fine carbides have vital contribution to mechanical properties during the service.