Calcium silicon alloy is a composite alloy composed of elements silicon, calcium, and iron. It is an ideal composite deoxidizer and desulfurizer. It is widely used in the production of high-quality steel, low-carbon steel, stainless steel, and other steel types and special alloys such as nickel-based alloys and titanium-based alloys; it is also suitable as a warming agent for converter steel-making workshops; it can also be used as a cast iron Inoculants and additives in the production of ductile iron.
Both calcium and silicon have a strong affinity with oxygen, especially calcium, which not only has a strong affinity with oxygen but also with sulfur and nitrogen, so calcium silicon alloy is an ideal compound. Glue oxygen agent, desulfurizer. Silicon alloy not only has strong deoxidation ability, and the deoxidation products are easy to float and be discharged, but it can also improve the properties of steel and improve the plasticity, impact toughness, and fluidity of steel. At present, calcium silicon alloy can replace aluminum for final deoxidation. It is used in the production of high-quality steel, special steel, and special alloys, such as rail steel, low carbon steel, stainless steel, and other steel types and special alloys such as nickel-based alloys and titanium-based alloys. Calcium silicon alloys can be used as deoxidizers. Calcium silicon alloy is also suitable as a temperature-increasing agent for converter steel-making workshops. Calcium silicon alloy can also be used as an inoculant for cast iron and an additive in the production of ductile iron.
1. Introductionof of Calcium silicon
A binary alloy composed of silicon and calcium belongs to the category of iron alloys. Its main components are silicon and calcium, and also contains varying amounts of impurities such as iron, aluminum, carbon, sulfur, and phosphorus. In the steel industry, it is used as a calcium additive, deoxidizer, desulfurizer, and denaturant for non-metallic inclusions. Used as an inoculant and denaturant in the cast iron industry. Calcium silicon alloys are divided into different categories according to calcium and silicon content:
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 separately according to different uses. In addition, on the basis of silicon-calcium alloy, other elements are added to form a ternary or multi-element composite alloy. Such as Si-Ca-Al; Si-Ca-Mn; Si-Ca-Ba, etc., used as deoxidizers, desulfurizers, denitrification agents, and alloying agents in iron and steel metallurgy.
2. Brief history of Calcium silicon
The French BOZEL General Electrochemical Company used the electric silicon thermal method around 1907 and later used the electric carbothermal method to produce calcium silicon alloys in electric furnaces. China smelted calcium silicate in a calcium carbide factory in Taiyuan in the 1950s. In 1964, the Beijing Ferroalloy Factory successfully developed a process for smelting calcium silicon alloys using layered feeding methods.
3. Properties of Calcium silicon
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 calcium vapor pressure and temperature is:
In the formula, pCa is the vapor pressure of calcium, Pa; T is the temperature, and 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 generated between Ca and CaSi below 910°C. CaSi2 (58.36%Si) is a peritectic compound generated between CaSi and Si below 1020°C. The phase composition of industrially produced calcium silicon alloy is CaSi2 about 77%, CaSi 5% to 15%, Si free <20%, and SiC <8%. The density of calcium silicon alloy containing 30% to 33% Ca and about 5% Fe has a density of about 2.2g/cm3 and a melting temperature range of 980 to 1200°C.
4. Application of Calcium silicon
Since calcium has a strong affinity with oxygen, sulfur, hydrogen, nitrogen, and carbon in molten steel, calcium silicon alloy is 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 the molten steel, which stirs the molten steel and is beneficial to the floating of non-metallic inclusions. After calcium silicon 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 silicon 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. Adding calcium silicon alloy can eliminate problems such as nodules at the ladle nozzle of steel using aluminum as the final deoxidizer, and blockage of the tundish nozzle in continuous steel casting | ironmaking. In the outside-furnace refining technology of steel, calcium silicate powder or core wire is used for deoxidation and desulfurization to reduce the oxygen and sulfur content in the steel to very low levels; it can also control the form of sulfide in the steel and improve the utilization rate of calcium.
In the production of cast iron, in addition to deoxidizing and purifying, calcium silicon alloy also plays a nurturing role, helping to form fine-grained or spherical graphite; it can evenly distribute graphite in gray cast iron and reduce the tendency of whitening; it can also increase silicon and desulfurize, improve the quality of cast iron.
5. Production process of Calcium silicon
It is generally believed that the chemical reaction expression for smelting calcium silicon alloy is CaO+SiO2+3C→CaSi+3CO↑
However, at high temperatures, lime and silica first form calcium silicate slag with a lower melting point, making it difficult for the carbon reduction reaction to proceed. Calcium has a low boiling point and is easily volatile to produce calcium vapor. Moreover, SiO2 is reduced to SiO (gas), so the gases discharged from the furnace are CO, Ca (gas), and SiO (gas). The loss of calcium and silicon in the furnace gas is about 10% each. SiO (gas) and Ca (gas) react with carbon when passing through the material layer, and most of them are converted into CaC2 and SiC. Therefore, the reactivity of the carbonaceous reducing agent is very important for smelting calcium silicon alloy.
Calcium oxide and silica react with carbon at high temperatures to form CaC2 and SiC, which are intermediate products in the production of calcium silicon alloys. Finally, part of it remains in the slag, so the production of calcium silicon alloy is smelting by the slag method. In essence, the methods for industrial production of calcium silicon alloys are all achieved by using CaC2 as the transition product. The density of calcium silicon alloy is slightly smaller than that of slag.
During the smelting process, calcium silicon alloy is basically concentrated in the upper part of the molten pool. This is a characteristic of smelting calcium silicon alloy. Special measures must be taken to separate it from the slag when it comes out of the furnace. Based on the above analysis, there are three processes for smelting calcium silicon alloys using the electric carbothermal (reduction) method, namely the mixed feeding method, the layered feeding method, and the calcium carbide method. The electrosilicothermal (reduction) method is also one of the methods for producing calcium silicon alloys.