Abstract:

The effects of basicity of refining slag and Al₂O₃ content on non-metallic inclusions in U75V steel were studied. The results showed that the basicity of refining slag had a great influence on the inclusions in steel. In the refining process of U75V steel, with the increase of basicity of refining slag from 1.4 to 2.0, the composition of inclusions in steel  changed greatly. The average mass fraction of CaO increased from 43% to 62%, while the average mass fraction of SiO₂, MgO and Al₂O₃ decreased from 37 %、16 % and 4 % to 8 %, 9 % and 2 % respectively. The basicity of refining slag had a great influence on the number density of inclusions in U75V steel. When the basicity was 1.4, the number density of inclusion was 2.95/mm². With the increase of basicity to 1.8, the number density of inclusion decreased to 1.42/mm², and the number density of inclusion began to increase. When the basicity of refining slag was 1.8, the number density of inclusion in steel was the lowest, and the refining slag was more conducive to the removal of inclusion. Al₂O₃ content in refining slag had an important effect on inclusions in steel. With the increase of Al₂O₃ content from 0 to 3%, the contents of CaO and SiO₂ in the inclusions decreased, while the contents of MgO and Al₂O₃ increased. The mass fraction of Al₂O₃ in the refining slag was increased to 6 %, and the mass fraction of CaO in the inclusion remained stable at about 40 %, while the content of MgO and SiO₂ decreased slightly, and the mass fraction of Al₂O₃ increased to about 18 %. With the increase of Al₂O₃ content in slag, the number density of inclusion in steel increased continuously, and when Al₂O₃ mass fraction in slag increases from 3 % to 6 %, the number density of inclusion increased by nearly one time. Therefore, U75V needs to control the Al₂O₃ mass fraction in refining slag below 3 %. In the process of production, Al_s and Al₂O₃ content in alloy and slag-making materials should be strictly controlled, Al₂O₃ content in slag should be reduced, and basicity of slag should be controlled at about 1.8.

Key words:

refining slag, basicity, U75V, Al₂O₃ content in slag, non-metallic inclusion