A Brief Understanding of Calcium Silicide Alloys

A binary alloy composed of silicon and calcium belongs to the category of ferroalloys. Its main components are silicon and calcium, and it also contains different amounts of impurities such as iron, aluminum, carbon, sulfur and phosphorus. The iron and steel industry is used as calcium additives, deoxidizers, desulfurizers and denaturants of non-metallic inclusions. The cast iron industry is used as an inoculant and denaturant. Silicon-calcium alloys are classified according to different calcium and silicon contents, and other impurities are otherwise specified for different purposes. In addition, on the basis of silicon-calcium alloy, other elements are added to form a ternary or multiple composite alloy. Such as Si-Ca-Al; Si-Ca-Mn; Si-Ca-Ba, are used as deoxidizer, desulphurizer, denitrification agent and alloying agent in steel metallurgy.

1. Brief history of calcium silicide alloy

The French BOZEL (BOZEL) General Electrochemical Company used the electric silicon heating method in 1907, and then used the electric carbon heating method to produce calcium silicide alloy in an electric furnace. China smelted calcium silicon in a calcium carbide plant in Taiyuan in the 1950s. In 1964, Beijing Ferroalloy Factory successfully studied the process of smelting calcium silicide alloy by layered feeding method.

2. Nature of calcium silicide alloy

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:


In the formula, pCa is the vapor pressure of calcium, Pa; T is the temperature, K. Silicon and calcium produce three compounds, namely CaSi, Ca2Si and CaSi2. CaSi (41.2% Si) is stable at high temperatures. 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 when the temperature is lower than 1020℃. The phase composition of the industrially produced calcium silicide alloy is about 77% CaSi2, 5%-15% CaSi, Si free <20%, and SiC <8%. The density of calcium silicide alloy containing 30% to 33% Ca and about 5% Fe is about 2.2g/cm3, and the melting temperature ranges from 980 to 1200°C.

3. The use of calcium silicide alloy

Since calcium has a strong affinity with oxygen, sulfur, hydrogen, nitrogen, and carbon in molten steel, calcium silicide alloys are mainly used for deoxidation, degassing and fixing sulfur in molten steel. After calcium silicon is added to molten steel, it produces a strong exothermic effect. Calcium becomes calcium vapor in the molten steel, which has a stirring effect on the 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 the non-metallic inclusions are also changed. Therefore, calcium silicide 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 calcium silicide alloy can eliminate problems such as the nodulation of steel with aluminum as the final deoxidizer at the nozzle of the ladle, and the clogging of the nozzle of the tundish of continuous cast steel and ironmaking. In the steel out-of-furnace refining technology, silicon calcium powder or core wire is used for deoxidation and desulfurization to reduce the oxygen and sulfur content in the steel to a very low level. It can also control the sulfide form in the steel and increase the utilization rate of calcium. In the production of cast iron, in addition to deoxidation and purification, silicon-calcium alloy also plays a role of incubation, helping to form fine-grained or nodular graphite; uniform graphite distribution in gray cast iron, reducing white mouth tendency; and can increase silicon and desulfurize, Improve the quality of cast iron.

The calcium silicon cored wire can effectively improve the anisotropy of steel.