Effect of creep deformation on the microstructural evolution of 11CrMoVNb heat resistant steel

The effect of creep deformation on the microstructural evolution of an 11CrMoVNb ferritic heat resistant steel during high temperature creep tests was investigated. The creep test was performed within a temperatures range from 593 to 621 °C under different stress levels. For the detailed understanding of precipitate coarsening behavior, transmission electron microscopy (TEM) was used to analyze thin foils and replica films obtained from the crept specimens. The major precipitates were found to be M23C6, MX and Cr2N phases and there was no change in precipitation sequence during creep. Coarsening behavior of the precipitates and growth behavior of martensite laths of the crept specimens were carefully examined in both regions of the grip and gage parts of the specimens in order to identify the effect of creep deformation. On the whole, precipitate size increased with increasing creep rupture time. On the other hand, precipitate coarsening and martensite lath widening were pronounced in the gage part compared to those in the grip part. This suggests that the creep deformation accelerates the rates of precipitate coarsening and martensite lath widening.

► The coarsening rate of the precipitates was accelerated by applied stress.
► The coalescence of martensite laths was accelerated by applied stress.
► The Laves phase and Z-phase were not observed after creep.
► The predicted size of MX precipitates by MatCalc agreed well with measured size.