Iron ore is the main raw material for long process steelmaking in iron and steel enterprises, and more than 80% of them adopt long process steelmaking. As the substitute of iron ore, scrap steel is the raw material of short process steelmaking in iron and steel enterprises. How to make steel from iron ore?
The raw materials of blast furnace ironmaking are iron ore and coke, but there will be a further processing flow before iron ore and coke enter the blast furnace, namely iron ore sintering and coking coal. After the raw materials are solved, they will be put into the blast furnace, and these raw materials will be reduced into molten iron containing carbon in the blast furnace. The main purpose of a blast furnace is to remove a large amount of sulfur from iron ore resources. In addition, coking and sintering can remove some harmful impurities from iron and steel. The molten iron obtained will be transferred to the converter to remove excess carbon, oxygen, phosphorus, and residual sulfur. The specific processes include hot metal pretreatment, converter blowing (dephosphorization and decarbonization), refining (desulfurization, deoxidization and alloying), continuous casting, and finally, the finished steel will be obtained.
Reheating → charging → melting period → oxidation period → reduction period → tapping (casting ingot or billet)
Furnace repair: repair the furnace body to prepare for the next steelmaking process.
Loading: light and thin materials are used as the base, then large-scale scrap steel is used as the bottom, light materials are used as the top, and finally light and thin materials are used to fill the gap.
Melting: melting process is divided into point arc, well penetration, main melting and melting end heating parts. Generally, the lower voltage and current are used in the arc point period, and the larger secondary voltage and current are used in the well penetration period. The attention that the bottom of the furnace shall be protected. The highest voltage and current are used in the main melting period, and the time proportion of the main melting period is more than 70% of the whole process. The lower voltage and larger current are used in the heating period at the end of melting to protect the furnace wall.
Oxidation: after complete melting, more than 70% ~ 80% of phosphorus removal enters the oxidation period (usually higher than 80 ℃ of the melting point of steel). The main task of the oxidation period is to remove phosphorus and carbon from the molten steel, gas and inclusions and raise the temperature of high liquid steel.
Reduction: the main tasks of reduction period are deoxidation, desulfurization, alloying and temperature regulation.
Tapping: the tapping process can further deoxidize and desulfurize.
China is now in the stage of rapid development, and the demand for steel production capacity is different from before. At present, the technology of electric furnace can not support the demand for steel, so the long process steelmaking which can be mass-produced and can obtain more profits is more suitable for the demand for steel.
From the perspective of sustainable development, in the future, the remediation of environmental pollution will be more stringent. When the pollution penalty is greater than the profits of high converter steelmaking, long process steel plants will build more pollution treatment equipment to ensure green production. Coke enterprises and mines in the upper reaches of long process steel plants will also add corresponding pollution treatment equipment. This will inevitably increase the cost of long process steelmaking. When the cost of long process steelmaking is higher than that of short process steelmaking because of environmental protection, EAF steelmaking can become the mainstream steelmaking method.