Effect of molybdenum on the precipitation behavior in titanium microalloyed HSLA steels part I – precipitation in austenite

The carbide precipitation behavior in austenite of a 0.04%C-0.10%Ti-0.21%Mo microalloyed steel was investigated by the stress relaxation test 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 contained a certain amount of Mo. As compared with TiC particles in a Ti steel, (Ti,Mo)C particles in a Ti-Mo steel exhibit a superior coarsening resistance during the coarsening stage. The fraction of Mo in the (Ti,Mo)C particles decreases with longer isothermal holding time or particle growth, indicating that the high level of replacement of Ti by Mo in the TiC lattice is in a “metastable” state with respect to the equilibrium precipitation of (Ti,Mo)C in austenite. (AU) © 2015 Companhia Brasileira de Metalurgia e Mineração (CBMM)