Abstract: On the basis of thermodynamic calculations, Mg-treatment experiments were carried out in 120 t ladle. The results showed that the slow-release cored wires containing magnesium can be injected smoothly into molten steel. Total magnesium mass fraction in molten steel was measured in the range of 0.001 0 %-0.001 6 %. During the process, nitrogen pick-up was not found. However total oxygen mass fraction was decreased 50 %, also cleanliness of steel was improved. After Mg-treatment, inclusions in SPHC changed from Al2O3 to spinel or pure MgO, and the size decreased from 3-5 μm to 1-2 μm. The magnesium mass fraction in inclusions presented a good correspondence with addition of magnesium alloy.

Key words: Mg-treatment, Al-killed steel, inclusion, cleanliness