Abstract
The factors controlling the intergranular fracture of three 1Cr–0·5Mo steels, tested at 550°C, have been examined. Failure results from the nucleation and growth of grain-boundary cavities. It is shown that creep life is dependent on the maximum principal stress, and that variations in the rupture properties of the steels are controlled by their susceptibility to nucleate intergranular cavities. Increasing the metalloid element content and, in particular, increasing the austenitizing temperature from 930 to 1300°C resulted in an increase in the cavity nucleation rate and a concomitant decrease in the rupture life. The cavity nucleation rate was found to be dependent on the maximum principal stress and when this dependence is used in conjunction with a simple cavity diffusion growth model the stress-state dependence of rupture life and the effect of residuals and austenitizing temperature on fracture properties could be predicted. These results are discussed in terms of the material and fabrication factors and service conditions that designers and operators of high-temperature plants must consider so that the plant may be operated safely and efficiently.
MST/81
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