Selection of silicon carbide and carburizer materials

At present, the domestic market of silicon carbide products have black calcined coke, green, its purity is different, the price is not the same, different enterprises according to their own conditions and conditions can choose different silicon carbide products. The microstructure and properties of cast iron largely depend on the microstructure and quality of raw materials. Due to the influence of the heredity of graphite in pig iron, a lot of scrap and carburizing agent have to be used in EAF melting. The use of carburizing agent is very important, especially for cylinder block and cylinder head castings with high density requirements, it is necessary to use carburizing agent after high temperature graphitization. If there is no high temperature graphitized carburizing agent, it has more impurities and ash, and it takes a long time to diffuse into the molten iron. If the melting time is short, the composition of molten iron in the furnace is not uniform, and it is easy to cause shrinkage defects after pouring. In addition, the nitrogen content of carburizing agent without high temperature treatment is high, and the nitrogen content in molten iron increases when the nitrogen-containing scrap is encountered. When the nitrogen content reaches a certain level, crack like porosity defects will be formed in the casting. The carburizing agent of petroleum coke is made by calcining and purifying petroleum coke, and its appearance is round or polygonal. It is characterized by high carbon, low sulfur and low ash. It is an ideal carbonaceous material and reaction intermediate in metallurgy, chemical industry, machinery, electric power and other industries, and has been widely used. Types of carburizers

According to the different sulfur content, it can be divided into high sulfur coke (sulfur content is more than 3%) and low sulfur coke (sulfur content is less than 3%). Low sulfur coke can be used as anode paste and prebaked anode for aluminum plant and graphite electrode for iron and steel plant. High quality low sulfur coke (sulfur content less than 0.5%) can be used to produce graphite electrode and carbon additive. Low sulfur coke of general quality (sulfur content less than 1.5%) is often used to produce prebaked anode. Low quality petroleum coke is mainly used for smelting industrial silicon and producing anode paste. High sulfur coke is generally used as fuel for cement plants and power plants. In the smelting process, due to improper proportioning or charging and excessive decarburization, sometimes the carbon content in the steel does not meet the requirements of the top period, so it is necessary to add carbon to the liquid steel. The commonly used carburizers are carburized pig iron, electrode powder, petroleum coke powder, charcoal powder and coke powder. Petroleum coke with few impurities is used as carburizing agent when medium and high carbon steel is smelted in converter. The requirements of carburizing agent for top blown converter steelmaking are high fixed carbon, low ash, volatile, sulfur, phosphorus, nitrogen and other impurities, and dry, clean, moderate particle size.

Effect of particle size of carburizer

The process of using carburizer includes dissolution diffusion process and oxidation loss process. Different particle sizes of carburizers result in different dissolution diffusion rates and oxidation loss rates. The absorption rate of the carburizer depends on the comprehensive effect of the dissolution and diffusion speed and oxidation loss speed of the carburizer: in general, the particle size of the carburizer is small, the dissolution speed is fast, and the loss speed is large; the particle size of the carburizer is large, the dissolution speed is slow, and the loss speed is small. The choice of particle size of carburizer is related to furnace diameter and capacity. Generally, if the diameter and capacity of furnace are large, the particle size of carburizer is larger; otherwise, the particle size of carburizer is smaller. The grain size of crystal graphite is required to be 0.5-2.5mm for less than 1t EAF, 2.5-5mm for 1T-3T EAF, 5.0-20mm for 3t-10t EAF and 0.5-1mm for ladle.