Scrap steel is the primary raw material for arc furnace smelting. However, social (recycled) scrap often contains high levels of harmful elements such as Cu, Sn, As, and Pb, which are difficult to remove. The partial substitution of scrap steel with alternative materials—such as hot metal (pig iron), direct reduced iron (DRI), decarburized iron, iron carbide, and composite metal materials—can effectively improve this issue.
Pig Iron
Some technologies are widely applied by EAF including carbon oxygen gun, secondary combustion, oxygen nozzle technology, furnace gas secondary combustion technology, etc, oxygen supply intensity greatly improved. Correspondingly, it should increase the amount of carbon, the most effective method is to add iron hot metal(pig iron). When large amounts of hot metal to join, it will produce a large number of chemical heat able to be utilized, that electrifying time can be shortened.
In EAF process, technologies such as carbon-oxygen lances, secondary combustion systems, oxygen injection nozzles, and furnace gas afterburning are widely used, significantly increasing the oxygen supply intensity. To balance this, carbon content must also be increased, with the most effective method being the addition of hot metal (pig iron). When large quantities of pig iron are added, a significant amount of chemical heat is released, which can be efficiently utilized to shorten the power-on (melting) time.
Advantages of adding pig iron:
- Shortens the smelting cycle
- Enhances thermal efficiency
- Dilutes harmful impurities in molten steel
Direct Reduced Iron (DRI)
Direct reduction refers to the process of reducing iron ore or oxides into metallic iron at temperatures below their melting point, typically in shaft furnaces or rotary kilns. Based on the form of the product, DRI can be classified as sponge iron, metallized pellets, or hot briquetted iron (HBI). The process can be gas-based or coal-based.
Advantages of adding DRI:
- Low in harmful impurities such as P, S, and N; offers stable chemical composition
- Sponge iron and HBI can be continuously fed into the furnace, reducing power-off time and heat loss
- Promotes foam slag formation, which extends the life of furnace refractories and electrodes
Decarburized Pig Iron
Molten iron from the blast furnace is quenched using high-pressure water to form pig iron pellets (3–10 mm). These pellets are then decarburized in a rotary kiln at controlled temperatures.
Advantages of decarburized pig iron:
- Gangue content is 1–3% lower than that of DRI, reducing power consumption
- Lower sulfur and phosphorus content compared to DRI
- Surface FeO facilitates foam slag generation
Iron Carbide
Iron carbide is produced by reacting iron ore with preheated industrial gases (CO, CO₂, CH₄, H₂, and steam) in a fluidized bed reactor under specific temperature and pressure conditions.
Advantages of adding iron carbide:
- Suitable for producing low-nitrogen steel
- Foam slag formation is easier, even without injecting carbon powder
- Clean composition with low sulfur and phosphorus, reducing desulfurization costs per ton of steel
Composite Metal Materials
Composite metal materials are new charge materials developed to replace part of pig iron, pellets, or scrap steel.
Advantages of composite metal materials:
- Reduce oxygen consumption
- Lower energy usage
- Shorten the smelting cycle
To sum up, the partial substitution of scrap steel with alternative materials in EAF process helps to compensate for the limitations of scrap and significantly improves the purity of the molten steel.
