There are three main steelmaking methods: converter, electric furnace and flat furnace.
In the process of steelmaking, the charge is melted into several liquid phases, which do not melt each other at high temperature, and the steel and other impurities are separated. The impurity here is steel slag. It collects the oxide formed after furnace oxidation. The steelmaking process is generally carried out by controlling the steel slag. Whether the slag making system is suitable or not has a great influence on the removal speed and degree of impurities in steel water, as well as smelting time and furnace life.
After the charge is melted, the slag begins to form until tapping. The normal combustion temperature of limestone is 1000-1200 ℃, but the steel-making temperature is very high. In the process of converter steelmaking, the high pressure supersonic oxygen jet continuously impinges on the molten pool, and the temperature in the operation area reaches 2200-2700 ℃. EAF is mainly used for steelmaking, and the temperature of the arc action zone reaches 4000 ℃. Free lime is easy to over burn, with cracks or glass shell on its surface, obvious volume shrinkage and black color.
As the inner wall of furnace wall is easy to be damaged by machinery, eroded by molten steel and steel slag, and damaged by high temperature, it should be repaired. In steelmaking, a large amount of dolomite is used instead of part of lime. The main purpose of dolomite slagging process is to extend the service life of furnace lining. According to the solubility of MgO in slag, a certain amount of dolomite is added to the furnace. The magnesium oxide in slag reaches saturation state, and a small amount of solid magnesium oxide particles are precipitated, which makes the viscosity of slag increase obviously in the later stage. Adding dolomite slag to make up the furnace can greatly improve the furnace life.
The main sources of steelmaking slag are: oxides produced by the oxidation of various impurity elements (such as silicon, manganese, potassium, etc.) contained in steel (iron, water, scrap), sulfur and phosphorus are removed from molten iron by slag and flux added in slag, impurities brought by ore and sinter, oxide skin and other materials are added as oxidant or coolant, and refractory lining erosion or scouring materials Sediment impurities brought by raw materials.
In the process of steelmaking, there are inevitably free calcium oxide and magnesium oxide, among which there is no overburned calcium oxide and magnesium oxide. The latter reacts slowly with water and expands and cracks later. Therefore, as steel slag, it can not be used as aggregate in concrete.
However, as an admixture, steel slag powder plays an anti shrinkage role in concrete, which is the same as the mechanism of calcium oxide as expansion agent.
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