Abstract:In order to predict the composition range of CaO-Al2O3-SiO2-MgO inclusion with good deformability, the liquidus projection and the low melting point area size of CaO-Al2O3-SiO2-MgO system was first calculated and analyzed by thermodynamic software FactSage. Furthermore, the condition of forming CaO-Al2O3-SiO2-MgO inclusions with low melting point was thermodynamically discussed in case of valve spring steel 60Si2CrA.The results show that the low melting area of CaO-Al2O3-SiO2-MgO inclusion first increases with an increasing in the MgO or Al2O3 content, then decreases, and low melting area is the biggest when the content of MgO and Al2O3 is 15% and 20%, respectively. Low melting point area in CaO-Al2O3- SiO2-MgO system remarkably increases with addition of CaO, but which hardly changes with an increasing in the SiO2 content. If the inclusions composition fell on the low melting point area in CaO-Al2O3-SiO2-15%MgO system and CaO-Al2O3-SiO2-15%MgO system at 1873K refining temperature for 60Si2CrA steel, respectively, and also guarantee that [O] is as low as possible, the inclusions composition should be controlled to be the surrounding region in which the ratio of CaO/SiO2 is unity and the content of Al2O3 is 20% and the ratio of CaO/SiO2 is unity and the content of MgO is 15%, respectively, while the O and Al content in molten steel is 10~30 ppm and 10~45 ppm for the former, respectively. For the latter, the O and Al content in molten steel is 10~30 ppm and 15~40 ppm, respectively.