Selection and use of recarburizer

1. Introduction of recarburizer.

There are many types of carbon-increasing raw materials, and the production processes are also different. There are charcoal, coal, coke, graphite, etc., and there are many sub-categories under these categories. Recarburizer generally refers to that the recarburizer is graphitized. Under high temperature conditions, the carbon atoms are arranged in graphite micromorphology, so it is called graphitization. Increase the carbon content of the recarburizer, reduce the sulfur content, and reduce the content of impurities in the recarburizer through graphitization.

The use of recarburizers in the casting process can greatly increase the amount of scrap steel and reduce the amount of pig iron. The charging method is electric furnace smelting, and the recarburizer should be put into the furnace charge together with scrap steel, and a small amount can be added to the surface of the molten iron. However, it is necessary to avoid adding a large amount of carbon to the molten iron, so as to avoid excessive oxidation and the occurrence of insignificant carbon increase effect and insufficient carbon content. The addition amount is determined according to the proportion of other raw materials and the carbon content. For various cast irons, various types of recarburizers can be selected according to needs. Its recarburization characteristics select pure carbon-containing graphitized substances to reduce excessive impurities in the pig iron, and the appropriate selection of recarburization can reduce the production cost of castings.

The role of recarburizers.

Cast iron, cast steel, and castings all have carbon requirements, so the recarburizer, as the name implies, is to increase the carbon content in the molten iron. For example, the commonly used furnace materials during smelting are pig iron, scrap steel, and reheating materials. The carbon content of pig iron is relatively high. However, the purchase price is higher than that of scrap steel, so increasing the amount of scrap steel and reducing the amount of pig iron, plus the recarburizer, can play a role in reducing the cost of castings.

Third, the choice of recarburizer.

There are many types of recarburizers, and there are many materials that can be used as cast iron recarburizers, but the quality is very different, and the price difference is large. Under the premise of the quality of castings, the recarburizer should be selected reasonably according to the characteristics and quality requirements of the company's products .

Judging from the use of most foundry companies, only two commonly used recarburizers are briefly introduced.

An artificial graphite.

Among ordinary carbides, artificial graphite is used.

The main raw material of artificial graphite is powdered calcined oil coke, in which pitch is added as a binder, and a small amount of other auxiliary materials are added. After the various raw materials are matched, they are pressed into a shape, and then processed at 2500~3000℃ in a non-oxidizing atmosphere to obtain graphitization. After high temperature treatment, ash, sulfur and flue gas are significantly reduced.

In view of the high price of artificial graphite products, most of the artificial graphite recarburizers used in foundries are chips, waste electricity and graphite blocks recovered from graphite electricity during the production process to reduce production costs.

The second is petroleum coke.

Crude coke is a commonly used recarburizer.

Petroleum coke, a by-product produced in the refining process of crude oil, residual oil and petroleum pitch obtained by the atmospheric distillation or vacuum distillation of crude oil, can be used as raw materials for the production of petroleum coke, and then coking to produce petroleum coke. The raw oil coke has a high impurity content and cannot be used directly as a recarburizer. It should be calcined first. Refining coke is calcined to remove sulfur, moisture and volatiles. Calcining petroleum coke at 1200~1350 degrees Celsius can get basically pure carbon.

How to use carbon-increasing substances.

Problems that should be paid attention to in the use of recarburizers.

Ignore when adding recarburizer.

The recarburization time is too early, it is easy to make it adhere to the vicinity of the furnace bottom, and the recarburizer adhering to the furnace wall is not easy to melt into the molten iron. On the contrary, if the carbon addition time is too late, the opportunity for carbon addition will be lost, resulting in slower smelting and heating time. This will not only delay the time of chemical composition analysis and adjustment, but also cause harm due to overheating. Therefore, in the process of adding metal charge, it is better to add recarburizer or bit by bit.

If the dosage is too large at one time, it can be used in combination with the molten iron overheating operation of the induction electric furnace. The absorption time of the recarburizer in the molten iron is 10min. On the one hand, electromagnetic stirring can make the recarburizer fully diffuse and absorb, and the absorption effect. In addition, it can also reduce the nitrogen content in the recarburizer.

2. Improve joining methods.

It is not possible to add one batch at a time, add in batches, and then melt a part, put a part (about a package of molten iron into the package), and then add carbon powder 1-2 times in the furnace, then slag and add alloy.

The aspects that need to be paid attention to are as follows:

1. Recarburizer is difficult to absorb (not calcined)

The second is the uneven distribution of multi-particle ash of the carbonizing agent.

3. Participation time is too late.

Fourth, the joining method is incorrect, use layered joining. Do not add it when there is too much slag on the molten iron mirror.

5. Try not to use too much rusty materials.

When factories purchase recarburizers, they generally pay attention to the following aspects: the price of recarburizers; the fixed carbon, sulfur, ash, volatile, and moisture content in the recarburizers, although these substances are important for stabilizing product quality, Reducing production costs is very important, but the nitrogen content in recarburizers is often ignored, because nitrogen is a gas after all, and it is not easy to detect and control. Therefore, when buying recarburizers, try to buy recarburizers with low nitrogen content.