Abstract：The formation mechanism of calcium-containing inclusions during the production of Q345D steel was investigated through industrial trials. Thermodynamic calculations are used to study the transformation mechanism of inclusions during solidification. The results showed that calcium in steel mainly comes from VD vacuum and calcium treatment. The CaO content of inclusions before vacuum is very low. However, after vacuum break, CaO content of inclusions increased due to entrainment. After calcium treatment, CaO content of inclusions further increased. The composition of the inclusions changed significantly during solidification. The content of CaO in inclusions of slab decreased significantly, and the content of CaS increased significantly, which is consistent with the thermodynamic calculation results. The large-sized calcium-containing inclusions in slab are mainly divided into calcium aluminate, calcium aluminate surrounded by CaS, calcium aluminate with spinel surrounded by CaS, CaS and Al2O3 bonding type, and CaS and spinel bonding type. The larger the inclusion size is, the higher the content of CaO is. The content of CaS in large-size inclusions is extremely low.
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2020, Vol. 55 
