Recarburizer for Casting Iron Foundry Moisture 0.5% max N Content % 200ppm max

In the smelting process, due to improper ingredients or improper loading and excessive decarburization, the carbon content in the steel sometimes fails to meet the requirements of the top stage. At this time, carbon is added to the molten steel. Commonly used recarburizers include carbon-increasing pig iron, electrode powder, petroleum coke powder, charcoal powder and coke powder. In the case of converter smelting medium and high carbon steel, petroleum coke containing little impurities is used as a recarburizer. The requirement for the recarburizing agent for top-blown converter steelmaking is that the fixed carbon is high, the content of ash, volatile matter and sulfur, phosphorus, nitrogen and the like is low, and it is dry, clean and moderate in particle size.

Its fixed carbon composition is:

w(C)>96%, volatile matter ≤1.0%, w(S)≤0.5%, w(moisture)≤0.55%, particle size is 1-5mm.

The particle size is too fine to be easily burned, and when it is too thick, it floats on the surface of the molten steel and is not easily absorbed by the molten steel. For the induction furnace, the particle size is 0.2-6mm, wherein the steel and other ferrous metals have a particle size of 1.4-9.5mm, the high carbon steel requires low nitrogen, the particle size is 0.5-5mm, etc., and the specific need to smelt the workpiece according to the specific furnace type. The specific types and details of the specific judgment and selection.

1. Furnace input method:

The recarburizer is suitable for melting in an induction furnace, but it is not the same depending on the process requirements.

(1) The use of a recarburizer in the intermediate frequency electric furnace smelting can be added to the lower part of the electric furnace according to the ratio or carbon equivalent requirement, and the recovery rate can reach above 95%;

(2) If the amount of carbon is insufficient to adjust the carbon content, firstly clean the slag in the furnace, add the carbon-increasing agent, and increase the carbon solution by electromagnetic heating, electromagnetic stirring or manual stirring, and the recovery rate can be about 90%. The low-temperature carbonization process is adopted, that is, when only a part of the charge is melted, and the temperature of the molten iron is low, all the carbon-reducing agents are added to the molten iron at one time, and the solid charge is pressed into the molten iron to prevent the iron from being exposed. Liquid surface. This method can increase the carbon content by more than 1.0%.

2. Carbon increase outside the furnace:

(1) Spray graphite powder inside the bag

The graphite powder is used as a recarburizer, and the blowing amount is 40kg/t, which is expected to increase the carbon content of the molten iron from 2% to 3%. As the carbon content of the molten iron gradually increases, the utilization rate of carbon decreases, the temperature of the molten iron before the carbon addition is 1600 ° C, and the average after the carbon increase is 1299 ° C. Spray graphite powder to increase carbon, generally using nitrogen as carrier, but under industrial production conditions, it is more convenient to use compressed air, and oxygen in compressed air produces CO, chemical reaction heat can compensate part of temperature drop, and CO reducing atmosphere is beneficial to Improve carbonization.

(2) Use of recarburizer when tapping

The 100-300 mesh graphite powder recarburizer can be placed in the bag or flushed with the flow from the iron tapping tank. After the molten iron is discharged, the carbon is dissolved and absorbed as much as possible, and the carbon recovery rate is about 50%.

Recarburizers can be used as a material for cast iron recarburizers, and artificial graphite, calcined petroleum coke, natural graphite, coke, anthracite, and mixtures made of such materials are commonly used.

Artificial graphite

Among the above various recarburizing agents, 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 a binder, and a small amount of other auxiliary materials are added. After the various raw materials are mixed, they are press-formed and then treated in a non-oxidizing atmosphere at 2500 to 3000 ° C to make them graphitized. After high temperature treatment, the ash, sulfur and gas contents are greatly reduced.

Due to the high price of artificial graphite products, the artificial graphite recarburizers commonly used in foundries are mostly recycled materials such as chips, waste electrodes and graphite blocks when manufacturing graphite electrodes, so as to reduce production costs.

When smelting ductile iron, in order to make the metallurgical quality of cast iron superior, the artificial carbon should be preferred.

2. Petroleum coke

Petroleum coke is a widely used recarburizer.

Petroleum coke is a by-product of refined crude oil. Residual oil and petroleum asphalt obtained by vacuum distillation or vacuum distillation can be used as raw materials for petroleum coke, and then coke is obtained to obtain raw petroleum coke. The production of raw petroleum coke is less than 5% of the amount of crude oil used. The annual production of petroleum coke in the United States is about 30 million tons. The raw petroleum coke has high impurity content and cannot be directly used as a recarburizer. It must be calcined first.

Raw petroleum coke has spongy, needle-like, granular and fluid states.

Sponge petroleum coke is produced by a delayed coking process. It is usually used as a fuel for calcination because it has a high sulfur and metal content, and can also be used as a raw material for calcining petroleum coke. The calcined sponge coke is mainly used in the aluminum industry and as a recarburizer.

The acicular petroleum coke is obtained by a delayed coking process using a raw material having a high content of aromatic hydrocarbons and a low impurity content. This coke has a needle-like structure that is easily broken, sometimes referred to as graphite coke, and is mainly used for the manufacture of graphite electrodes after calcination.

Granular petroleum coke is a hard granule. It is a raw material with a high content of sulfur and asphaltene. It is produced by delayed coking and is mainly used as a fuel.

The fluid petroleum coke is obtained by continuous coking in a fluidized bed. It is in the form of fine particles, has no directional structure, high sulfur content and low volatile content.

The calcination of petroleum coke is to remove sulfur, moisture, and volatiles. Calcination of raw petroleum coke at 1200~1350 °C can make it a substantially pure carbon.

The largest user of calcined petroleum coke is the aluminum industry, and 70% is used to make anodes that reduce bauxite. Calcined petroleum coke produced in the United States accounts for about 6% of cast iron recarburizers.

3. Natural graphite

Natural graphite can be divided into two types: flake graphite and microcrystalline graphite.

Microcrystalline graphite has a high ash content and is generally not used as a carbon reinforcer for cast iron.

There are many varieties of flake graphite: high carbon flake graphite needs to be extracted by chemical methods, or heated to high temperature to decompose and volatilize the oxides. This flake graphite has low yield and high price, and generally does not act as a recarburizer; low carbon flakes Graphite has a high ash content and should not be used as a recarburizer; it is mainly used as a carbon reinforcer for medium carbon graphite, but it is not used in large amounts.

4. Coke and anthracite

In the electric arc furnace steelmaking process, coke or anthracite may be added as a recarburizer during charging. Induction furnace smelting cast iron is rarely used as a recarburizer because of its high ash and volatile content.