The role of petroleum carbonization agent and cast iron pretreatment agent in the casting process

1. Strong deoxidation effect, purifying molten iron, reducing slag inclusion and porosity defects; Reduce wall thickness sensitivity, make the tissue denser, smooth the cutting surface, and significantly improve machinability.
——Due to the presence of FeO, the melting point of any slag can decrease. Therefore, at any given temperature, the decrease in the melting point of slag will cause more slag to become liquid. For example, when the FeO content in the slag is 10%, its melting point will be 1350-1400 ℃. In addition, under the strong stirring effect of the coreless induction furnace, this liquid slag will be "homogenized" in the melt, leaving millions of very small slag particles in the melt. Many surface defects of the casting are caused by the high FeO and MnO slag (usually referred to as manganese silicate slag) with good fluidity being brought into the mold. If a pre-treatment agent is added, due to the reduction reaction of the pre-treatment agent, the FeO content of this slag will be reduced to 1 or 2%, and its melting point will be raised to 1500-1550 ℃. Therefore, at the usual tapping temperature (1500-1550 ℃), this slag either remains solid or only a small amount becomes liquid, thus retaining a large monomer in the furnace. This makes the slag particles easy to be removed due to their high upward velocity, and greatly reduces the chance of them being brought into the mold and causing casting defects.
——Pre treatment agents have a deoxidizing effect in castings, which can react with oxygen in the casting furnace during melting, thereby reducing excess oxygen. They can also have a deoxidizing effect during melting and in the front ladle, thereby reducing the generation of pores and slag inclusions.
2. Increase fluidity, stabilize the composition of molten iron, prevent segregation, and reduce white and shrinkage defects
——The dispersed FeO-SiO2 fine inclusions in the molten iron are not easy to float out and detach from the molten iron, which is one of the important reasons for the decrease in fluidity of the molten iron, the decrease in shrinkage ability, the increase in shrinkage tendency, and the obvious white tendency. By adding a pre-treatment agent and undergoing a reduction reaction with iron oxide, the well reduced pure molten iron has enhanced its filling and shrinking abilities.
3. Reduce undercooled graphite in gray cast iron, promote the generation of A-type graphite, enhance control over graphite morphology, and reduce the tendency for white casting, thereby optimizing the mechanical properties of castings
——There are high-density dislocations around the pre-treatment agent particles, and the increase in crystallization leads to grain refinement and changes in graphite morphology. The length of graphite becomes shorter, A-type graphite increases, D-type graphite decreases, and the number of eutectic clusters and pearlite significantly improves.
4. For ductile iron, it is a powerful deoxidizer. Adding it in ductile iron production can increase the number of graphite balls, improve the spheroidization rate, make the graphite balls more round and small, and reduce the amount of spheroidizing agent added.
Petroleum carbonization agent
——Due to the higher content of FeO in ductile iron slag compared to gray iron or creep iron slag, the problems caused by fluidized slag on ductile iron are more serious than those caused by gray iron or creep iron. Therefore, adding a pretreatment agent to ductile iron will have a better effect.
5. Enhance the nucleation ability of graphite and increase the graphite core, effectively solving the problem of fertility decline. It can create a long-term and stable core for graphite precipitation and growth, with strong nucleation ability. It has the function of promoting and stabilizing nucleation, alleviating the melting of graphite cores during long-term high temperature (1520-1550 ℃) settling of molten iron (conventional operation in casting is to settle at high temperature of 1520-1550 ℃ to purify molten iron, while also ensuring the pouring temperature), and effectively compensating for the loss of graphite cores.
6. Eliminate the oxidation factors of molten iron, reduce furnace lining oxidation, and extend furnace lining life by 30% -100%. The use of carburizer during casting can significantly increase the amount of scrap steel, reduce the amount of pig iron, or eliminate pig iron. The feeding method for electric furnace melting should include adding carbon additive along with scrap steel and other furnace materials, and small doses can be added to the surface of the molten iron. However, it is necessary to avoid feeding large quantities into the molten iron to prevent excessive oxidation, which may result in unclear carbonization effect and insufficient carbon content in the castings. The amount of carbon additive added is determined based on the ratio and carbon content of other raw materials. Different types of cast iron, choose different types of carburizers according to needs. The characteristics of the carbon additive are that it selects pure carbon containing graphitic substances to reduce excessive impurities in pig iron. Choosing the appropriate carbon additive can reduce the production cost of castings. Carbonizing agents are suitable for melting in induction furnaces, but their specific use varies depending on the process requirements.
(1) The use of carburizer in medium frequency electric furnace melting can be added to the lower part of the furnace according to the ratio or carbon equivalent requirements, with a recovery rate of over 95%;
(2) If the carbon content is insufficient to adjust the carbon content, the slag in the furnace should be cleaned first, and then a carbon additive should be added. The carbon can be dissolved and absorbed by heating the iron liquid, electromagnetic stirring or manual stirring, and the recovery rate can be around 90%. If a low-temperature carbon additive process is used, that is, only a part of the furnace material is melted, and the temperature of the melted iron liquid is low, all the carbon additive should be added to the iron liquid at once, and solid furnace material should be pressed into the iron liquid to prevent it from exposing the surface of the iron liquid. This method can increase the carbonization of molten iron by over 1.0%.
2. Carbon addition outside the furnace:
(1) The graphite powder is used as a carbon enhancer for spraying graphite powder inside the package, with a blowing rate of 40kg/t. It 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 carbonization is 1600 ℃, and the average temperature after carbonization is 1299 ℃. Spraying graphite powder for carbonization generally uses nitrogen as the carrier, but under industrial production conditions, compressed air is more convenient. Moreover, the combustion of oxygen in compressed air produces CO, and the heat of chemical reaction can compensate for some of the temperature drop. Moreover, the reducing atmosphere of CO is conducive to improving the carbonization effect.(2) When using a carbonization agent during iron tapping, 100-300 mesh graphite powder carbonization agent can be placed in the bag or flushed into the iron tapping tank with the flow. After the iron liquid is discharged, it should be thoroughly stirred to dissolve and absorb the carbon as much as possible, and the carbon recovery rate is about 50%.