Effect of molybdenum addition on the precipitation of carbides in the austenite matrix of titanium micro-alloyed steels

The present work aims to reveal the effect of Mo on the precipitation behavior of MC-type (M = Ti and Mo) carbides in the austenite matrix of titanium micro-alloyed steel. The precipitation start-time-temperature curve was determined by a double-pass compression test on a Gleeble simulator, and the elemental mass fraction of MC-type carbides was measured by a physical-chemical phase analysis after a single-pass rolling test. The results shows that 0.2 wt% Mo accelerates the precipitation kinetics of MC-type carbides. During the initial stage of precipitation, Mo tends to distribute in the outer region of precipitates by replacing Ti despite of the high solubility of MoC in austenite. The replacement of Ti by Mo in TiC lattice leads to two opposite effects: First, it restrains MC precipitation due to the higher Gibbs free energy of (Ti, Mo)C relative to TiC; Second, it promotes MC precipitation by decreasing the interfacial chemical energy of MC/austenite system. The second effect is more pronounced during the initial stage of precipitation when MC precipitates are relatively small and hence MC precipitation is accelerated by Mo addition. Compared to TiC, (Ti, Mo)C with stronger coarsening resistance suppresses austenite recovery and recrystallization more effectively, which favors maintaining the deformation microstructures at high temperatures.