Study on the nucleation and growth of M23C6 carbides in a 10% Cr martensite ferritic steel after long-term aging

In the 10% Cr martensite ferritic steel, it is found that most of M23C6 carbides appear on high angle boundaries (HABs) with a misorientation angle of 40 degrees-60 degrees and only a small amount of them precipitate at low angle boundaries (LABs) with a misorientation angle of 8 degrees-15 degrees. It has always been considered that V is added to mainly form MX carbides. However, in the present work, V will also diffuse into M23C6 carbides after aged at 650 degrees C for 12,000 h, which not only replaces Fe but also W and Mo. From the initial state to 25,000 h, the variation of the mean size of M23C6 basically obeys the Lifshitz-Slyozov-Wagner coarsening theory. When the V content in M23C6 gradually increases from 12,000 h to 25,000 h, the coarsening rate of M23C6 decreases remarkably. The V in M23C6 plays an important role in controlling the coarsening of M23C6 carbides in this stage. (C) 2015 Elsevier Inc. All rights reserved.