low sulfur, low nitrogen recarburizer
The common recarburizer (graphite petroleum coke, calcined petroleum coke and calcined anthracite coal,semi graphite petroleum coke), for cast iron is a kind of carbonaceous material, the main component is carbon.Carbonaceous materials mainly include graphite and amorphous carbon.Graphite is a hexagonal lamellar crystal. The carbon atoms in the graphite crystal are arranged in layers. The covalent bonds between the atoms in the same layer are combined with strong binding force.However, the polar bond between layers is weak.
Therefore, graphite is easy to be delaminated and has very low strength.Because graphite crystals have such structural characteristics, it is easy to grow into sheet structures when growing in molten iron.Amorphous carbon is also a hexagonal lamellar crystal, different from graphite in that the hexagonal arrangement is not complete and the distance between the layers is slightly larger.
Classification of recarburizer
According to the crystal structure of carbon additive, carbon additive can be divided into amorphous and crystalline state.According to the existence of carbon additive, divided into Graphite petroleum coke and Non-graphite petroleum coke.Graphite petroleum coke mainly graphite electrode, graphite electrode scraps and debris, natural graphite granule, microcrystalline ink, etc.In addition, silicon carbide (SiC) has a hexagonal structure similar to graphite, and is also listed as a special form of graphite petroleum coke.Non-graphite petroleum coke mainly includes asphalt coke,calcined petroleum coke,coke press, forging burned anthracite, etc.
Principle of carbonization
Carbon in the elemental form of carbon additive, melting temperature of 3727℃, cannot be melted at the temperature of molten iron, therefore, the carbon in the carbon additive is mainly dissolved in molten iron by dissolution and diffusion in two ways.When the WC of molten iron is 2.1%, the graphite in the carbon additive can be directly dissolved in molten iron.The direct solution of non-graphite carbon is basically non-existent, but with the passage of time, the carbon gradually diffuses and dissolves in the molten iron.Therefore, for electric furnace melting synthetic cast iron carburizing, graphite carburizing rate is significantly higher than that of non-graphite carburizing agent.
Data suggest that the dissolution of carbon in molten iron is affected by the transmission of the liquid boundary layer on the surface of solid particles.Comparing the results obtained from coke and coal particles with those obtained from graphite, it is found that the diffusion and dissolution rate of Graphite petroleum coke in molten iron is obviously faster than that of coke and coal particles.Partially dissolved coke and coal particles were observed by electron microscopy. It was found that a thin layer of sticky ash was formed on the surface of the samples, which was the main reason affecting the diffusible solubility of coke and coal particles in molten iron.
Selection of recarburizer
For electric furnace smelting, the core of carburizing technology is the use of high quality carbon additive.Referring to the relevant information, it is considered that the selected recarburizer should have the following characteristics:
(1)select after high temperature graphitization treatment of carbon additive, only after high temperature treatment, carbon atoms can from the original disorderly arrangement into sheet arrangement, flake graphite can become the best core of graphite nucleation, promote graphitization.
(2)The sulfur content of good carbon additive is very low, WS < 0.03% is an important index.
(3)The porosity of carburizing agent is also very important to the effect of carburizing agent and the absorption rate of carburizing agent. Therefore, the high quality green petroleum coke is better than the electrode graphite.