Silicon calcium is a binary alloy composed of silicon and calcium, belonging to the category of ferroalloy. Its main components are silicon and calcium, and it also contains impurities such as iron, aluminum, carbon, sulfur and phosphorus in varying amounts. Iron and steel industry used as calcium additives, deoxidizer, desulfurizer and nonmetallic inclusions denaturant. Cast iron industry used as inoculant and denaturant.
Silicon calcium application：
Because calcium has a strong affinity with oxygen, sulfur, hydrogen, nitrogen and carbon in liquid steel, calcium silicon alloy is mainly used for deoxidation, degassing and fixing sulfur in liquid steel. The addition of silicon calcium to molten steel produces a strong exothermic effect.
Calcium becomes calcium vapor in the molten steel, which has stirring effect on the molten steel and is beneficial to the floating of non-metallic inclusions. After the deoxidation of Si-Ca alloy, the non-metallic inclusions with large 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 for the production of clean steel, 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 in the ladle, and the blockage of the water mouth of the intermediate tank of continuous cast steel |.
In the process of steel refining, calcium silicon powder or core wire is used to deoxidize and desulphurize, so that the content of oxygen and sulfur in steel is very low. 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 or spherical graphite; Make the graphite distribution in gray cast iron uniform, reduce the white tendency; And can increase silicon, desulfurization, improve the quality of cast iron.
Silicon calcium production process:
1.mixed feeding method
The operation of the mixed charging method is similar to the operation of the small electric furnace to produce 75% ferrosilicon, but the silica-calcium alloy charge is not all mixed into the furnace, but some of it is in the form of partial charging, and 1/4 to 1/3 of the silica is added to the electric level after the falling of the material, and the wood block is added separately, and the rest of the silica and lime, coke, and bituminous coal are mixed into the furnace.
2.layered feeding method
The layered feeding method is to mix lime with the corresponding amount of coke (according to the coke required to generate low-grade calcium carbide) and concentrate it into the furnace, after it is cleared, silica and the remaining reducing agent are mixed and then added. The operation process of the layered feeding method can be divided into three stages:
① Tethering stage. After iron production, the temperature in the furnace decreases, so it must be raised. Its operation is: discharge level after iron, ramming furnace, taking out hard blocks, finishing the material surface, piercing and breathable, strengthening the material surface maintenance, giving full load, deep plug level, this stage is generally 1 hour and 20 minutes.
② CaC2 generation phase. When the temperature in the furnace increases, remove the floating material around the electric stage, pick up the viscous material, quickly mix the added lime and the corresponding reducing agent, all directly added to the orange vortex around the electric stage. In order to accelerate the generation of CaC2, we should try to give full load and strive for early capping material. The duration of this stage is generally 30-40 minutes, and cannot be too short or too long. The time is too short, the CaC2 is not sufficient, and a large amount of CaO that does not participate in the reaction will react with SiO2 added later into salt. Too long, calcium volatilization and heat energy loss increase, alloy Ca content decreases, unit power consumption increases.
③ Silica destroys CaC2 to form CaSi alloy stage. After CaC2 is generated, the mixture is added, and SiO2 in the mixture is used to destroy CaC2 and generate CaSi alloy. After adding the material, cook it until it comes out.
The following operation should be evenly fed, carefully maintain the furnace condition, increase the permeability of the material surface, ensure that the electric level is deeply and steadily inserted into the charge, prevent the collapse of the material from burning, in order to reduce the volatilization and heat loss of Ca. The smelting time at this stage is generally 2.5-3 hours.
The duration of this phase should not be too long or too short. Too long, the volatilization and heat loss of Ca increase, the alloy contains low Ca, the unit power consumption increases; Too short, a large amount of CaC2 and SiO2 do not fully react, the amount of slag increases, the calcium in the alloy is low, and the amount of silicon and calcium generated is small.
Iron and alloy casting, normally every 4-5 hours out of the furnace. When drawing iron, use round steel or burners to open the outlet, and hot metal and slag flow into the tundish at the same time. Since the slag density is greater than the alloy density, the alloy must be in the slag separator for 2-4 minutes, and after the alloy is completely floating, the alloy is slowly poured into the ingot mold. When it is found that the alloy surface is white and shiny, the casting is stopped immediately to avoid the alloy slag inclusion. After condensation, the alloy is demoulded and finished in storage.
CaC2 was first prepared in an electric furnace with CaO > 85% of high quality lime and carbonaceous reducing agent. Then the cooled CaC2 was broken and then added with silica and carbonaceous reducing agent to produce silica-calcium alloy in another electric furnace. The equipment conditions and operation methods required for the two-step production of silicon-calcium alloy are basically the same as those for the production of ferrosilicon. Although this method can obtain a longer furnace life and a higher product grade rate, but the need for two electric furnaces, high comprehensive power consumption, high operation requirements, difficult to control the process, the water requirements in the raw material is strict, so only in the high degree of automation, good management conditions, mechanized feeding, silo seal good electric furnace used.