Microstructure and Mechanical Properties of 9Cr1Mo Steel-12Cr2Si Steel Bimetallic Billet Produced by Centrifugal Casting

Lead cooled fast reactor (LFR) is one of the next generation of nuclear plants. Tubes in LFR coolant system requires high temperature strength and Lead-Bismuth eutectic (LBE) corrosion resistance and. 9Cr1Mo steel - 12Cr2Si steel bimetallic billet that satisfies above properties has been produced by dual centrifugal casting. Bimetallic billet was normalized for 1 hour at 1050°C and air cooled. After normalizing, tempering was performed for 1 hour at 750°C and air cooled. Mechanical properties of 9Cr1Mo material satisfied ASME Code Section II Part A SA-426 CP91 standard. 9Cr1Mo steel has tempered martensite structure and 12Cr2Si steel has tempered martensite-ferrite mixed structure. The width of mixed zone was about 1000μm. The LBE corrosion resistance was indirectly verified by observation of oxide layer. After heat treatment, hardness of 9Cr1Mo steel was about 240Hv and 12Cr2Si steel was about 200Hv. As a result of high temperature tensile test, the suitable hot work temperature range was 1000°C and 1100°C. Thermo-Calc calculation result shows that the austenite phase fraction was major factor to the workability of the billet.