Effect of carbon content on the mechanical properties of 10Cr–5W ferritic steels

The effect of carbon content on the microstrucures, the tensile strength, creep strength and fracture toughness of 10Cr–5W ferritic steels containing from 0.02 to 0.13 mass% C is investigated. The low carbon steels possess the higher Ms temperature than the high carbon steels, so that the packet size of the martensite structure is larger in the low carbon steels. Both the FATT (fracture appearance transition temperature) and the USE (upper shelf energy) increase with decreasing carbon content. This means the decrease of toughness and the increase of ductility with decreasing carbon content. Fine precipitates of the Laves phase are observed in the martensite lath in all experimental steels after quality heat treatment. The tensile strength measured at 873 K has a tendency to increase with decreasing C content. But a certain amount of C is needed even in 5 W ferritic steels to keep the longer creep-rupture life under the lower stress level.