| A study has been made to investigate the effect of tungsten(W) addition on the microstructures, tensile properties and low cycle fatigue(LCF) properties of 9Cr-1Mo steels at 298K and 873K. Four steels containing different amount of W (0W, 1.2W, 1.8W and 2.7W) were normalized at 1050℃ for 1 hour and tempered at 750℃ for 1 hour. Microstructural analysis revealed that no significant difference was observed in their tempered martensite microstructure of 0W, 1.2W and 1.8W, but δ-ferrite was observed to form at the prior austenite grain boundaries of 2.7W alloy. With the increase in W content, the yield and tensile strength were increased at both temperatures. Low cycle fatigue life was also increased with the W content up to 1.8%, but decreased in the 2.7W alloy, which was primarily due to the presence of soft δ- ferrite acting as a crack initiation site. The fatigue life of 873K was reduced as compared to that of 298K, due not only to the decrease in the strength at high temperature but also to the formation of oxide layers along slip bands, which increases slip irreversibility during cyclic deformation. |
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