Other impurities are otherwise specified according to different uses. In addition, on the basis of the silicon-calcium alloy, other elements are added to form a ternary or multi-component composite alloy. Such as Si-Ca-Al; Si-Ca-Mn; Si-Ca-Ba, etc., used as deoxidizer, desulfurizer, denitrification agent and alloying agent in iron and steel metallurgy.
Calcium is an alkaline earth metal, the atomic weight is 40.08, the outer electronic structure is 4S2, the density (20℃) is 1.55g/cm3, the melting point is 839±2℃, and the boiling point is 1484℃. The relationship between the vapor pressure of calcium and temperature is:
In the formula, pCa is the vapor pressure of calcium, Pa; T is the temperature, K. Silicon and calcium generate three compounds, namely CaSi, Ca2Si and CaSi2. CaSi (41.2%Si) is stable at high temperature. Ca2Si (29.5%Si) is a peritectic compound formed between Ca and CaSi at temperatures below 910 °C. CaSi2 (58.36%Si) is a peritectic compound formed between CaSi and Si below 1020℃. The phase composition of industrially produced silicon-calcium alloys is about 77% of CaSi2, 5% to 15% of CaSi, free of Si <20%, and SiC <8%. The density of silicon-calcium alloy containing Ca 30%-33% and Fe about 5% is about 2.2g/cm3, and the melting temperature range is 980-1200℃.
Because calcium has a strong affinity with oxygen, sulfur, hydrogen, nitrogen and carbon in molten steel, silicon-calcium alloys are mainly used for deoxidation, degassing and fixation of sulfur in molten steel. The addition of silicon calcium to molten steel produces a strong exothermic effect. Calcium turns into calcium vapor in molten steel, which has a stirring effect on molten steel, which is beneficial to the floating of non-metallic inclusions. After the silicon-calcium alloy is deoxidized, non-metallic inclusions with larger particles and easy to float are produced, and the shape and properties of the non-metallic inclusions are also changed. Therefore, silicon-calcium alloy is used to produce clean steel, high-quality steel with low oxygen and sulfur content, and special performance steel with extremely low oxygen and sulfur content. The addition of silicon-calcium alloy can eliminate the nodules at the ladle nozzle of steel using aluminum as the final deoxidizer, and the clogging of the tundish nozzle of continuous casting steel | iron making. In the out-of-furnace refining technology of steel, silicon-calcium powder or core wire is used for deoxidation and desulfurization, so that the content of oxygen and sulfur in steel is reduced to a very low level; it can also control the form of sulfide in steel and improve the utilization rate of calcium. In the production of cast iron, in addition to deoxidation and purification, silicon-calcium alloy also plays a role in inoculation, which helps to form fine-grained or spheroidal graphite; makes the graphite in gray cast iron evenly distributed and reduces the tendency of white mouth; and can increase silicon and desulfurization. , to improve the quality of cast iron.