Raw materials required for steelmaking and requirements for each raw material

1. Raw materials for steelmaking

Metal materials: molten iron, scrap steel, alloy steel

Non-metallic materials: slagging agent (lime, fluorite, iron ore), coolant (scrap steel, iron ore, iron oxide), carburizing agent and fuel (coke, graphite seeds, coal blocks, heavy oil)

Oxidant: oxygen, ironstone, iron scale.

2. Raw material requirements

Metal

1. molten iron

Molten iron is the main raw material for converter steelmaking, generally accounting for 70%-100% of the charge. It is the main heat source for converter steelmaking. The requirements for molten iron are: (1), composition (2), slag content (3), temperature .

Element

1), Silicon (Si)

Silicon is an important heat-generating element. The high Si content in the molten iron increases the chemical heat in the furnace. The Si content in the molten iron increases by 0.10%, and the amount of scrap steel added can increase by 1.3%-1.5%.

The Si content in the molten iron is high and the amount of slag increases, which is beneficial to dephosphorization and desulfurization.

Excessive silicon content will increase the slag and consumption, easily cause splashing, and reduce the metal yield. At the same time, excessive silicon dioxide in the slag will also intensify the erosion of the furnace lining, affect the lime slag rate, and extend the blowing time. Usually, the silicon content in molten iron is 0.30%-0.60%.

2), Manganese (Mn)

Manganese is a heat-generating element. MnO formed after the oxidation of Mn in molten iron can effectively promote the dissolution of lime, accelerate slag formation, and reduce the amount of flux and furnace lining erosion.

At the same time, the molten iron contains high Mn and the residual manganese in the final steel is high, which can reduce the manganese ferroalloy required for alloying and help improve the purity of the molten steel.

The ratio of manganese to silicon required for molten iron for converters is 0.8-1.0. Currently, low-manganese molten iron is used more often, with a manganese content of 0.20%-0.80%.

3), Phosphorus (P)

Phosphorus is a high-heating element and a harmful element to general steel types. Therefore, the lower the phosphorus content of the molten iron, the better. Generally, the molten iron P is required to be ≤0.20%.

4), Sulfur (S)

In addition to the easy cutting of sulfur, most steel types require the removal of sulfur, a harmful element. The desulfurization efficiency of oxygen converter single slag operation is only 30%-40%. my country's steelmaking technical regulations require that the sulfur content of the molten iron entering the furnace should not exceed 0.05%.

Requirements for slag amount carried by molten iron

Blast furnace slag contains high amounts of sulfur, Si0, and Al203. Excessive blast furnace slag entering the converter will lead to a large amount of steel slag in the converter, increase lime consumption, cause splashing, and reduce the life of the furnace lining. Therefore, the molten iron entering the converter will require that the amount of slag carried should not exceed 0.5%.

Requirements for molten iron temperature

The temperature of the molten iron is a symbol of the physical content of the molten iron. The physical heat of the molten iron accounts for 50% of the heat income of the converter. Efforts should be made to ensure the temperature of the molten iron entering the furnace, sufficient heat source in the furnace and rapid slag formation. my country's steelmaking regulations stipulate that the temperature of the molten iron entering the furnace should be greater than 1250°C and should be relatively stable.

2. Scrap steel

Both converter and electric furnace steelmaking use scrap steel. The amount of scrap steel used in oxygen top-blown converter is generally 10%-30% of the total charge.

Requirements for scrap steel in converter steelmaking

1) Overall dimensions and blockiness of scrap steel

It should be ensured that it can be smoothly added to the converter from the furnace mouth. The length of scrap steel should be less than 1/2 of the diameter of the converter mouth, and the unit weight of scrap steel should generally not exceed 300kg. The national standard requires that the length of scrap steel should not be greater than 1000mm, and the maximum weight of a single piece should not be greater than 800kg.

2) Scrap steel must not be mixed with ferroalloys

It is strictly prohibited to mix copper, zinc, lead, tin and other non-ferrous metals and rubber, and it is not allowed to mix closed containers, explosives, flammable and explosive materials and toxic substances. The sulfur and phosphorus content of scrap steel is not more than 0.050%.

3) Scrap steel should be clean and dry

It must not be mixed with sand, cement, refractory materials, oil, etc.

4) Classified storage of scrap steel of different properties

Non-alloy steel and low-alloy steel scrap can be mixed together, and alloy scrap steel and pig iron are not allowed to be mixed. Alloy scrap steel should be stored separately to avoid smelting difficulties, smelting scraps or waste of valuable alloy elements.

3. Ferro Alloy

Commonly used iron alloy types simple alloys: Fe-Mn, Fe-Si, Fe-Cr, Fe-V, etc.

Composite deoxidizer: Ca-Si alloy, Al-Mn-Si alloy, Mn-Si alloy, etc.

Pure metals: Mn, Ti, Ni, Al.

Non-metallic

1. Slag-forming agent

(1) Lime

The main component of the slag-making material in the alkaline steelmaking method is Ca0, which is burned from limestone. It is an indispensable material for P and S removal, and the dosage is relatively large.

Its quality has a major impact on the blowing process, product quality and furnace lining life. Therefore, lime has high Ca0 content, low Si0, and S content, low raw and over-burning rate, high activity, and moderate lumpiness. In addition, the lime should be kept clean, dry, and fresh.

(2) Fluorite

The main component of fluorite is CaF, and the characteristics of fluorite fluxing when roasted at about 930C are fast action and short time. However, using large amounts of fluorite will increase splashing, aggravate furnace lining erosion, and pollute the environment.

(3)Dolomite

The main component of dolomite is CaCO3.MgC03. After roasting, it can become light-burned dolomite, whose main component is Ca0.Mg0. The converter uses raw dolomite or light-burned dolomite to replace part of the lime to make slag. It can reduce the erosion of furnace lining by slag and improve the service life of furnace lining.

(4)Synthetic slagging agent

Synthetic slagging agent is made by adding an appropriate amount of lime, fluorite, manganese oxide or other oxides and other fluxes, and preforming it at low temperature. It has a low melting point, high alkalinity, uniform composition, small particle size, and is easily broken at high temperatures and has a fast slagging speed, thus improving the metallurgical effect and reducing the slagging load of the converter.

2. Carburizing agent

During the smelting process, due to improper ingredients or charging and excessive decarburization, the carbon content in the steel sometimes does not meet the expected requirements. At this time, carbon must be added to the molten steel. Commonly used carburizing agents include carburized pig iron, electrode powder, petroleum coke powder, charcoal powder and coke powder.

In converter smelting, petroleum coke containing few impurities is used as a carburizing agent for high-carbon steel.

Oxidizing Agent

Oxygen is the main oxidant for converter steelmaking. Its purity reaches or exceeds 99.5%. The oxygen pressure must be stable and moisture must be removed.

Iron oxide, also known as iron phosphorus, is an oxide shell produced during the heating, rolling and continuous casting of steel billets. The iron content accounts for about 70%-75%. Iron oxide scale also contributes to slagging and cooling. When used, it should be heated and baked to keep it dry.

Iron ore, the oxides of iron in iron ore exist in the form of Fe2O3, Fe3O4, and FeO, with the oxygen content being 30.06%, 27.64%, and 22.28% respectively.

Thank you for reading, follow us to share more knowledge about #steelmaking and #ferroalloys. #AnyangLishiIndustrial has focused on the research and development of ferroalloy production and sales for more than 20 years.