Study on Microstructure of directional solidified T91 steel

Using the method of directional solidification to prepare T91 steel is an effective way to reduce the elastic modulus and improve the thermal fatigue properties of alloy. In this paper, T91 steels were fabricated through liquid metal cooling method by the solidification rate of 30 mu m/s, 90 mu m/s and 180 mu m/s, and the crystal morphology was analysed. The results demonstrate that deflection angle of columnar crystals is increased with the raising of solidification rate, the maximum angle is 20 degrees, and the solidification structure is refined in general. The central solidification zone is the concentration area of directional microstructures, in which lath ferrites are arranged in parallel and the martensites are mainly distributed in the beginning and the end of the sample. The range of elastic modulus values of three specimens is 141.05 similar to 186.73GPa, and E-90 mu m/s<E-180 mu m/s<E-30 mu m/s<E-common (cast). The thermal fatigue property of T91 obtained by directional solidification method is better than that by common casting. When the solidification rate is 90 mu m/s, the thermal fatigue resistance of the specimen is best, which increases by about 25%.