Carbide precipitation in austenite of a Ti-Mo-containing low-carbon steel during stress relaxation

The carbide precipitation behavior in austenite of a 0.04%C-0.10%Ti-0.21% Mo micro-alloyed steel was investigated by the stress relaxation method and transmission electron microscopy. Results showed that the precipitation-time-temperature diagram for carbide precipitation exhibited a typical “C” curve, the nose of which was located at about 925 °C. The carbide was identified as a (Ti, Mo)C particle with a NaCl-type crystal structure that contains a certain amount of Mo. As compared with TiC particle in Ti steel, (Ti, Mo)C particle in Ti-Mo steel exhibits a superior coarsening resistance during the coarsening stage. The fraction of Mo in (Ti, Mo)C particle decreases with isothermal holding time or particle growing, indicating that the high level replacement of Ti by Mo in TiC lattice is in a “metastable” state with respect to the equilibrium precipitation of (Ti, Mo)C in austenite.