Effects of combining niobium and molybdenum in HSLA steels: from austenite conditioning to final microstructure

Three main topics are covered in this paper regarding Nb-Mo interactions in microalloyed steels. First, the synergistic behavior of Nb and Mo in enhancing solute drag effects and modifying recrystallization and precipitation kinetics in austenite under hot working conditions is analyzed. Then, the effect of different microalloying additions on the final phase transformations is examined. In addition to composition and austenite conditioning effects on the phases formed and the corresponding CCT diagrams, a quantitative study using an EBSD technique is described which was performed in order to measure unit size distributions and homogeneity of complex microstructures. Finally, the contribution of different strengthening mechanisms to yield strength is evaluated for different coiling temperatures and compositions. (AU) © 2015 Companhia Brasileira de Metalurgia e Mineração (CBMM)