Summary：Understanding and function of carburizer, and selection of high quality carburizer. The problems that should be paid attention to in use are analyzed, and the correct use of carburizer is expounded。

一、Description of Carburizer

There are many kinds of raw materials and production processes of carburizers,There are wood carbon, coal carbon, coke, graphite, etc。High quality carburizer generally refers to the graphitized carburizer. Under high temperature conditions, the arrangement of carbon atoms is in the micro form of graphite, so it is called graphitization。Graphitization can reduce the content of impurities, increase the carbon content and reduce the sulfur content.
When the carburizer is used in casting, the amount of scrap can be greatly increased, and the amount of pig iron can be reduced or pig iron is not used.In the charging mode of electric furnace smelting, the carburizer should be put in together with the scrap steel and other furnace materials, and the small dosage can be added on the surface of molten iron。However, it is necessary to avoid mass feeding of molten iron, so as to prevent excessive oxidation, which leads to the situation that the carburizing effect is not obvious and the carbon content of castings is not enough。The amount of carburizer is determined according to the proportion and carbon content of other raw materials。Different types of cast iron, according to the need to choose different types of carburizer. The characteristic of carburizer is to choose pure graphitized material containing carbon to reduce excessive impurities in pig iron. The proper selection of carburizer can reduce the production cost of castings。

二、Function of carburizer

For casting, cast iron, cast steel and castings, there will be a requirement for carbon. As the name implies, the carburizer is to increase the carbon content in the molten iron. For example, in smelting, the common furnace materials are pig iron, scrap and return furnace materials. The carbon content of pig iron is high, but the purchase price is higher than that of scrap steel, so increase the scrap steel input and reduce the pig iron input, Adding carburizer can reduce the cost of casting.

三、Selection of Carburizer

There are many kinds of carburizers, and there are many materials that can be used as carburizers for cast iron, but there is a great difference in quality and price. On the premise of ensuring the quality of castings, we should correctly select the carburizers according to the characteristics and quality requirements of the products of the enterprise.According to the use of most foundries, only two kinds of commonly used carburizers are briefly introduced.
1、Artificial Graphite
Among the commonly used carburizers, the best quality is artificial graphite。
The main raw material for the manufacture of artificial graphite is powdered high-quality calcined petroleum coke, in which asphalt is added as binder, and a small amount of other auxiliary materials are added. After all kinds of raw materials are matched, they are pressed into shape, and then treated in a non oxidizing atmosphere of 2500-3000 ℃ to graphitize. After high temperature treatment, the ash content, sulfur content and gas content are greatly reduced.Because of the high price of artificial graphite products, most of the common artificial graphite carburizers used in foundry are recycled materials such as chips, waste electrodes and graphite blocks in order to reduce the production cost.
2、Green Petroleum Coke
Petroleum coke is a widely used carburizer。
Petroleum coke is a by-product of refining crude oil. The residual oil and petroleum asphalt obtained from the constant pressure distillation or vacuum distillation of crude oil can be used as raw materials for the production of petroleum coke, and then raw petroleum coke can be obtained after coking. Raw petroleum coke has a high content of impurities, so it can not be used as a carburizer directly, but must be calcined first. Petroleum coke is calcined to remove sulfur, moisture and volatile matter. Calcining crude petroleum coke at 1200-1350 ℃ can make it a basically pure carbon.

四、How to use carburizer

Problems in using carburizer
1、The addition time of carburizer should not be neglected. 
If the adding time of carburizer is too early, it is easy to adhere to the bottom of the furnace, and the carburizer attached to the furnace wall is not easy to melt into the molten iron. On the contrary, if the adding time is too late, the opportunity of carbon addition will be lost, which will cause the delay of melting and heating time.This not only delays the time of chemical composition analysis and adjustment, but also may bring harm due to over heating. Therefore, it is better to add the carburizer little by little in the process of adding the metal charge.For example, in the case of a large amount of one-time addition, it can be considered in combination with the overheating operation of the molten iron used in the induction furnace to ensure that the absorption time of the carburizer in the molten iron is 10min. On the one hand, the carburizer can be fully diffused and absorbed through the electromagnetic stirring to ensure the absorption effect. On the other hand, it can reduce the nitrogen content in the carburizer.
2、Improvement in addition method
Do not add it in one time, add it in batches, melt and add a part at last, put a part (about a package) of molten iron into the package, and then return to the furnace for 1-2 times, slag and add alloy.
There are several aspects to pay attention to： 
1.Carburizer is difficult to absorb (without calcination)
2.Uneven distribution of ash particles in carburizer
3.Join too late
4.The adding method is wrong, and layered adding is adopted. Avoid adding too much slag to the molten iron mirror
5.Try not to use too much rusty material
When purchasing carburizers, foundries generally pay attention to: first, the price of carburizers; second, the fixed carbon, sulfur, ash, volatile and water content of carburizers. Although these are very important to stabilize the quality of products and reduce the production cost, an important parameter is often ignored, that is, the nitrogen content of carburizers. Because nitrogen is a gas after all, it is not easy to test and control, Therefore, it is better to try to buy a carburizer with low nitrogen content.