Improvement on High-Temperature Mechanical Properties of Modified 9Cr-1Mo Steel Through Intermediate Hot Rolling

Abstract

Modified 9Cr-1Mo steel is a candidate material for high-temperature (~650 °C) application in the development of Generation-IV nuclear reactors. In the present investigation, intermediate hot rolling on modified 9Cr-1Mo steel have been performed in austenitic phase (1050 °C) and below austenitic phase (550 °C). Intermediate hot rolling including normalization at elevated temperature (1150 °C), followed by tempering (700 °C) is employed to refine its lath structure and improve precipitation state. The modified 9Cr-1Mo steel rolled at 1050 °C with 30% deformation showed improvement on both strength and toughness, which may be attributed to increase in area fraction of M23C6/MX precipitates and higher dislocation density. A typical mode of tensile fracture with radial cracks and axial splitting is observed in the testing temperature between −196 and 20 °C. These cracks are caused by a high fracture stress generated in perpendicular direction during necking since stress triaxiality increases as necking is deepened. However, such radial cracks are found completely absent in the test temperature between 100 and 650 °C.