Effect of Rare Earth-Magnesium Alloy on Inclusion Evolution in Industrial Production of Die Steel

Rare earth metals and magnesium are important purifying elements in steel. However, most scholars mainly focused on the cleanliness of molten steel by adding single rare earth or adding single magnesium. There are few reports on the simultaneous addition of rare earth and magnesium metals to steel. In this paper, rare earth-magnesium alloy is added to a hot work die steel in industrial production. Combined with thermodynamic calculation, the effect of rare earth-magnesium alloy on the evolution of inclusions was studied. The results show that composite inclusions of Ce2O2S and CeS attached or wrapped by MgO are formed after adding rare earth-magnesium alloy. With the help of low-density MgO, the composite inclusions containing high-density Ce inclusions are promoted to float up. Thermodynamic calculation indicates that the addition of magnesium changes the formation tendency of rare earth inclusions. With the increase of magnesium content in steel, the stability area of Ce inclusions will move from the Ce2O2S stability area slightly close to the Ce2O3 stability area to the direction of the CeS stability area, which will improve further the desulfurization ability. The thermodynamic analysis is in good agreement with the test results.