Influence of Mo on Growth and Coarsening of Nanometer-sized Carbides in Low-alloy Ferritic Steels Containing Ti

By optical microscopy, transmission electron microscopy and energy dispersive spectroscopy, the changes with aging time in size, composition and distribution of nanometer-sized (Ti, Mo)C precipitated in Ti-Mo low-alloy ferritc steel have been studied in comparison with that of nanometer-sized TiC precipitated in Ti low-alloy ferritc steel. It was found that the growth rate of (Ti,Mo) C in Ti-Mo steel was less than that of TiC in Ti steel. Nanometer-sized carbides formed at 650 degrees C (or 550 degrees C) for 55 h were at transitional stage from growth to coarsening. When aging time reaches 55 h, the coarsening rates of nanometer-sized carbides in Ti and Ti-Mo steel tend to be the same and invariable. The influence of Mo on growth and coarsening of nanometer-sized carbides tends to decrease with increasing aging time, and Mo contents in nanometer-sized carbides with the same size at different aging time were different.