Abstract
Modern advanced 9–12 % Cr steels are complex alloys with excellent creep strength even at high temperatures up to 620°C. The mechanical properties of these steels are significantly influenced by the presence and stability of various precipitate populations. Numerous secondary phases grow, coarsen and, sometimes, dissolve again during heat treatment and service, which leads to a varying obstacle effect of these precipitates on dislocation movement. In this work, the experimentally observed creep rupture strength of an modified 9–12% Cr steel developed in the European COST Group is compared to the calculated maximal obstacle effect (Orowan stress) caused by the precipitates present in these steels for different heat treatment conditions. It is shown that the differences in creep rupture strength caused by different heat treatments disappear after long time service. This observation is discussed on the basis of the calculated evolution of the precipitate microstructure. The concept of boosting long-term creep rupture strength by maximizing the initial creep strength with optimum quality heat treatment parameters for precipitation strengthening is critically assessed.
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Holzer, I., Kozeschnik, E. & Cerjak, H. New approach to predict the long-term creep behaviour and evolution of precipitate back-stress of 9–12% chromium steels. Trans Indian Inst Met 63, 137–143 (2010). https://doi.org/10.1007/s12666-010-0019-8
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DOI: https://doi.org/10.1007/s12666-010-0019-8