Effect of Cooling Conditions on the Size and Morphology Evolution of MgAl2O4 Inclusions in Al‐Deoxidized Steel Coupling with Mg Treatment

The experiment of Al‐deoxidized steel coupling with Mg treatment is conducted under three cooling methods to observe the size and morphology of MgAl 2 O 4 . Most of MgAl 2 O 4 in the water‐cooled steel are sphere or ellipsoid‐like shape, in the furnace‐cooled steel are cubic or octahedral‐like shape, and in the air‐cooled steel are irregular shape. The quantity of inclusions in the size of 1–3 μm increases with the increasing cooling rate, whereas the quantity of the other size decreases with the increasing cooling rate. The result shows that the changing of cooling methods has little effect on the critical size and the nucleation rate of MgAl 2 O 4 . The growth of MgAl 2 O 4 is effected by diffusion, Ostwald, and collision growth, and the increasing cooling rate leads to the decreasing growth time. The size of MgAl 2 O 4 is decided by the diffusion of Mg and the growth time of MgAl 2 O 4 . Four possible morphological transformation paths of MgAl 2 O 4 in steel are found, and the shape of MgAl 2 O 4 can evolve from sphere or ellipsoid to octahedron via truncated octahedron or cubic‐like shape. The final morphology of MgAl 2 O 4 is controlled by the transformation path which has a close relationship with the cooling rate.