Carbide precipitation in austenite of Nb–Mo-bearing low-carbon steel during stress relaxation

• Mo was incorporated into NbC lattice during precipitation in austenite.
• High level replacement of Nb by Mo in NbC lattice is metastable.
• (Nb, Mo)C particle showed a higher coarsening resistance than NbC particle.

The carbide precipitation in austenite of Nb–Mo bearing low-carbon steel was investigated by stress relaxation and transmission electron microscopy (TEM). The precipitation-time-temperature (PTT) diagram exhibits a typical “C” shape curve, the nose of which was located at 950 °C. Mo was found to be incorporated into NbC lattice to form a complex (Nb, Mo)C particle during precipitation. Compared to NbC particles in Nb-bearing steel, (Nb, Mo)C particles in Nb–Mo-bearing steel exhibit superior coarsening resistance.