Effect of Mg Addition on the Characterization of γ-α Phase Transformation During Continuous Cooling in Low Carbon Steel

The influence of magnesium on the phase transformation and mechanical properties has been investigated by means of dilatometric and microstructural analysis in low carbon microalloyed steel. The thermal simulation experiments were performed on a Gleeble-3800 system equipped with a high-speed deformation dilatometer. The results reveal that, by adding with Mg, the pearlite transformation is delayed, and the pearlite has a scattered distribution even at low cooling rates from 0.1 to 0.5 K/s. It also shows that Mg tends to promote the bainite transformation as a result of the formation of acicular ferrite and granular bainite. Acicular ferrite is attributed to the change of dominant oxide inclusions from inert Al2O3, to xMgO · Al2O3, which serves as an effective nucleant for acicular ferrite. Moreover, bainitic structure obtained by the addition of Mg into the molten steel exhibits the remarkable improvement of toughness and tensile properties.