Why does oxygen enter the molten steel during the steelmaking process?
During the steelmaking process, in order to remove harmful impurities such as carbon and sulfur from the molten iron, oxygen molecules need to be added to the molten iron by blowing oxygen or adding oxidants during the smelting process.
Generally speaking: the function of blowing oxygen is to oxidize and react with carbon, silicon, manganese, phosphorus, sulfur and other elements in the molten iron to form gases or oxides with higher melting points, thereby reducing these five impurities that are harmful to the composition of the molten steel. , and use the chemical heat released during the oxidation reaction to increase the temperature of the molten iron.
During the steelmaking process, oxygen plays a double-dealing role.
On the one hand, during the heating process of molten steel, oxygen is needed, and oxygen is also needed to chemically react with carbon, sulfur and other harmful substances in the molten steel to improve the quality of the steel.
On the other hand, oxygen molecules in molten steel will affect the mechanical properties and strength of the steel, so the molten steel must be deoxidized.
Oxygen itself has a negative impact on steelmaking.
The harmful effects of oxygen on cast steel are caused by the huge difference in the solubility of oxygen in liquid and solid steel.
The main harmful effects of oxygen on steelmaking are
1. Oxygen is one of the reasons for the formation of pores in steel castings
During the solidification process of molten steel, since the solubility of oxygen decreases significantly with the decrease of temperature, the precipitated oxygen reacts with the carbon in the molten steel, and the generated CO bubbles become pores if they remain in the steel.
2. Oxygen promotes the formation of hot cracks in cast steel
When the oxygen content of the molten steel is too high, the tendency of hot cracking of cast steel will be aggravated. The reason is that when FeO and FeS meet, they form a low melting point (940°C) eutectic (FeO·FeS) and distribute it in the form of a film on the grain boundaries. Easy to cause thermal cracking.
3. Oxygen is one of the main elements that forms non-metallic inclusions
Oxygen can react with various elements to form oxide inclusions. If these inclusions are retained in the steel, they will reduce the performance of cast steel.
Deoxidation requires the addition of elements that combine with oxygen and are easily removed from the molten steel into the slag.
According to the binding strength of various elements in molten steel to oxygen, the order from weak to strong is as follows: chromium, manganese, carbon, silicon, vanadium, titanium, boron, aluminum, zirconium, and calcium. Therefore, iron alloys composed of silicon, manganese, aluminum and calcium are commonly used for steelmaking deoxidation.
1. Ferro Silicon: The main elements of Ferro Silicon are iron and silicon. It is a commonly used deoxidizer in steelmaking and casting. The chemical affinity between silicon and oxygen is very high, and it can effectively convert oxygen into silicon dioxide. , adding a certain amount of silicon to steel can effectively improve the strength, hardness and elasticity of steel.
2. Metal silicon (Silicon Metal) is also a commonly used deoxidation material in steelmaking. It can effectively remove oxygen from molten steel and reduce the reaction capacity during smelting while deoxidizing, making deoxidation safer!
3.Silicon manganese alloy is an ferro alloy composed of manganese, silicon, iron, etc., and is the main alloying agent for steelmaking. Manganese exists in the solid solution state in steel and plays a strengthening role. It can increase the strength of ferrite, improve the mechanical properties of steel, and enhance the strength, ductility, toughness and wear resistance of steel. Silicon is present in steel in solid form and increases its strength, fatigue limit and resistance to corrosion and wear. Therefore, manganese-silicon alloy is an indispensable alloy agent in steelmaking.
4.aluminum ferro Pure aluminum has always been the main deoxidizer in the steelmaking industry. It is strictly controlled when producing killed steel grades with high ductility and high impact properties, especially low carbon killed steel grades suitable for making cold rolled sheets. Controlled elements; moreover, this type of steel requires more aluminum elements to refine the grains. However, since the specific gravity of aluminum is much smaller than that of molten steel, it floats on the surface of the molten steel when it is deoxidized and alloyed, and is easily oxidized and suffers large burning losses. This reduces the utilization rate of aluminum, increases the consumption of aluminum, and increases Reduce production costs and reduce economic benefits. In order to solve the above problems, the steel research department developed a new deoxidizer-aluminum iron deoxidizer.
5. Ferromanganese (Carbon Ferromanganese) The main elements of ferromanganese are manganese and iron. Ferromanganese is often used as a casting deoxidizer, desulfurizer and alloy additive. Using ferromanganese as a steelmaking material can effectively deoxidize and improve the quality of steel. Hardness and durability!
6. Silicon-barium multi-component alloy Silicon-barium is a new multi-component alloy. Its advantage is that the content can be customized, and the silicon element inside can also be customized to achieve more deoxidation!
7. Silicon slag is the bottom slag produced by smelting ferrosilicon and metallic silicon. It still contains a certain amount of silicon element inside. Silicon slag can be used as a deoxidizer in steelmaking, and can also be purified again to produce ferroalloy products with high silicon content. It can effectively reduce steelmaking costs and improve manufacturer efficiency and product quality.
