A new approach to improve creep resistance of high Cr martensitic steel

A modified 9Cr–1Mo steel was cooled to 200 °C from the normalizing temperature and then directly heated to the tempering temperature. It was found that the time to rupture at 650–700 °C for the steel heat-treated at 200 °C increased three times over than that of the modified 9Cr–1Mo steel conventionally normalized and tempered. The microstructure of the improved steel was tempered martensite and the size of martensite blocks was larger than for the conventional treatment. The hardness of the improved steel was adequately recovered after tempering. Aging tests showed that the particle sizes of Cr23C6 and VN type carbonitride in the improved steel were finer in the conventional steel. The above-mentioned heat treatment was applied to the reduced activation martensitic steel F-82H and the improvement was confirmed.