Silicon-calcium alloy is composed of silicon and calcium, which belongs to the category of ferroalloys. and it also contains impurities such as iron, aluminum, carbon, sulfur and phosphorus in varying amounts. In the iron and steel industry, it is used as a calcium additive, deoxidizer, desulfurizer and denaturant for non-metallic inclusions. It is used as an inoculant and denaturant in the cast iron industry. Calcium-silicon alloys are classified according to the content of calcium and silicon:
Grade Ca (not less than) Si
Ca31Si60 31 50~65
Ca28Si60 28 50~65
Ca24Si60 24 55~65
Ca20Si55 20 50~60
Ca16Si55 16 50~60
Other impurities are specified according to different purposes. In addition, on the basis of silicon-calcium alloys, other elements are added to form ternary or multi-element composite alloys. 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.
Property of Silicon Calcium
Calcium is an alkaline earth metal with an atomic weight of 40.08, an outer electronic structure of 4S2, a density (20°C) of 1.55g/cm3, a melting point of 839±2°C, and a boiling point of 1484°C. The relationship between the vapor pressure of calcium and temperature is
Where pCa is the vapor pressure of calcium, Pa; T is the temperature, K. Silicon and calcium form 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 at temperatures below 1020°C. The phase composition of industrially produced silicon-calcium alloys is about 77% CaSi2, 5% to 15% CaSi, free Si < 20%, and SiC < 8%. The density of silicon-calcium alloy containing 30% to 33% of Ca and about 5% of Fe is about 2.2g/cm3, and the melting temperature ranges from 980 to 1200°C.
Usage of Silicon Calcium
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. Calcium silicon produces a strong exothermic effect when added to molten steel. Calcium turns into calcium vapor in molten steel, which has a stirring effect on molten steel and 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 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 nodulation of the steel with aluminum as the final deoxidizer at the ladle nozzle, and the clogging of the tundish nozzle of continuous casting steel. In the refining technology outside the furnace of steel, silicon-calcium powder or core wire is used for deoxidation and desulfurization to reduce the content of oxygen and sulfur in steel 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 an inoculating role, which helps to form fine-grained or spherical graphite; makes the graphite in gray cast iron evenly distributed, reduces the whitening tendency; and can increase silicon and desulfurize , Improve cast iron quality.