Carburizers can be divided into calcined coal carburizers, petroleum coke carburizers, columnar graphite carburizers, and graphitized petroleum coke carburizers according to their raw materials and processing techniques.
1. Graphitized petroleum coke recarburizer
Among the recarburizers, the best quality is low-sulfur and low-nitrogen recarburizer, also known as artificial graphite. It can be used to smelt nodular cast iron to obtain high-quality castings.
Artificial graphite is calcined petroleum coke, adding asphalt as a binder, and then adding other auxiliary materials. After graphitization at a high temperature of 2500-3000 ° C, the content of ash, sulfur, and gas is greatly reduced. Artificial graphite is expensive, so the general recarburizer is made of cutting particles when manufacturing electrodes, or crushed waste electrodes. In addition, the tailings of negative electrode materials are also a good source of recarburizer. The most important indicator of artificial graphite is that the sulfur content is very low, between 0.01-0.07.
2. Petroleum coke: Calcined petroleum coke is a widely used recarburizer
After the raw petroleum coke is calcined at 1200-1350℃, it becomes calcined petroleum coke that can be used as a carburant. The sulfur content of calcined petroleum coke is between 0.02-3%, and the calcined petroleum coke between 0.02-0.5% can be used as a recarburizer.
3. Graphite cylinder recarburizer
Graphite recarburizer is a ferroalloy product that has been graphitized and rich in carbon elements. Graphite recarburizer has stable element properties and is often used in many industries. It is often used in steelmaking and casting. High-quality Graphite carburizer is an essential metallurgical material for the production of high-quality steel. Features No need to increase the use of special equipment. The graphite carburizer also has the advantage of effectively reducing energy consumption, which can effectively shorten the smelting time and quickly achieve the smelting effect.
4. Coke and anthracite
When cupola furnaces make iron, coke is used to increase carbon at the bottom, so the use of recarburizers in cupola furnaces is rare. In the process of electric furnace steelmaking, coke or anthracite is used as a carburant by adding coke or anthracite, and anthracite is more commonly used as a carburant. Due to the relatively high ash and volatile content of the two, they are rarely used as recarburizers for melting cast iron in induction furnaces.
The role of carburizing agent
Carburizer is an important raw material for melting molten iron in an induction furnace, and its quality and usage directly affect the quality of molten iron. Castings have certain requirements for carbon, so carburizers are used to increase the carbon content in molten iron. For example, pig iron, scrap steel, and recycled materials are commonly used in smelting. Although the carbon content of pig iron is high, the cost is relatively low. It is higher for scrap steel, so the use of carburizer can increase the amount of scrap steel and reduce the amount of pig iron, so as to reduce the cost of castings.
Characteristics of carburizer
Graphite recarburizer has the characteristics of high carbon (≥98%), low sulfur (≤0.05%), low N (≤600PPm), and high-temperature fusibility. For the purpose of increasing the tensile strength and reducing the cost, the tensile strength of the casting can be increased by 20—50Mpa.
The use of recarburizers in castings can effectively reduce production costs, and can also improve the smelting quality of castings. It is an indispensable additive in the cast iron smelting industry, and high-temperature graphitized recarburizers have fast absorption speed and high Carbon, low sulfur, high absorption rate and other characteristics.
Use of carburant
When using the carburant, try to put the carburant in the middle and lower part of the furnace, and add other charge on it. Here, the scrap steel charge is selected first. When the carbon content of the molten iron is lower, it is more conducive to the absorption of the carburant. . At the same time, it can also increase the contact surface and contact time between the carburizer and the molten iron, thereby improving the carburization efficiency. If a large furnace uses a large amount of recarburizer, it is recommended to add it layer by layer multiple times, which can better improve the dissolution rate and absorption rate of the graphitized recarburizer. At the same time, the carburizer is placed on the bottom of the furnace, which can also buffer the impact on the bottom of the furnace when the iron material is added. This can also protect the furnace lining. The carburizer is used in casting, which can greatly increase the amount of scrap steel, reduce or eliminate the amount of pig iron. So when we use it, we should use it correctly in order to achieve better cost savings.
The carburizer mainly affects the quality of castings by affecting the quantity and shape of graphite. When there are high requirements on the quality of castings, the value of carburizer cannot be compared completely through the price of unit carburization. Therefore, the comprehensive cost after use should be considered in combination with the impact on the quality of castings. At its root, the use of carburizers is mainly to improve the quality of casting products. For example: choosing the right material and using it properly can remove or reduce the whitening tendency of thin-walled castings and the shrinkage tendency of thick-walled castings. The choice of a good quality recarburizer is the premise. In addition, in the use method, if the use method is appropriate, the stability of the casting can be effectively improved, thereby reducing the production cost and improving the quality of the product.
The carburizing process using a carburant includes a dissolution diffusion process and an oxidation loss process. The particle size of the carburant is different, the dissolution diffusion rate and oxidation loss rate are also different. The absorption rate of the carburant depends on the combined effect of the dissolution and diffusion speed of the carburant and the oxidation loss speed: in general, the carburant particles are small, the dissolution rate is fast, and the loss rate is large; the carburant particles are large, The dissolution rate is slow and the loss rate is small. The selection of the particle size of the carburant is related to the diameter and capacity of the furnace. In general, the larger the diameter and capacity of the furnace, the larger the particle size of the carburant; on the contrary, the smaller the particle size of the carburant. For an electric furnace melting below 1 ton, the particle size of graphitized recarburizer is first selected from 0.2 to 2 mm. The grain size of crystal graphite smelted in a 1t～5t electric furnace is preferably 2～5mm. 5t ~ 10t electric furnace smelting crystal graphite particle size requirement is 3 ~ 8mm is suitable. The particle size of the graphitized recarburizer covered in the ladle is preferably 0.2-1 mm.