Effect of Prior Austenite Grain Size on High Temperature Creep Properties of a Cr-Mo-V Steel

The creep tests for the specimens with the various prior austenite grain sizes (10, 26, 52 and 106 μm in diameter) have been carried out at 650°C-617 kgf/mm2 to investigate the effect of the prior austenite grain size on high temperature creep properties of a 1Cr-1Mo-1/4V steel. The minimum creep rate decreased linearly with increasing prior austenite grain diameter up to 50 μm.This increase in the creep resistance was proportional to the decrease in the volume fraction of the recovered zone along the prior austenite grain boundaries. In the specimen with prior austenite grain diameter larger than 50 μm, however, the creep resistance did not follow the linear increase with the grain diameter, because of the formation of large cracks at higher stress, and the marked increase in the recovered zone width at lower stress due to the microstructural inhomogeneity. The prior austenite grain size should be controlled to be below 50 μm in diameter to optimize the creep resistance of a Cr-Mo-V rotor steel for the long term service.