Some Ferroalloy materials can be used as deoxidizers in steelmaking, such as ferro silicon, silicon manganese, ferromanganese, calcium silicon ferroalloy, etc.
What is the function of steelmaking deoxidizer? What are the main types of steelmaking deoxidizers? How do we choose a suitable deoxidizer?
Steelmaking deoxidizer is an additive used in the steel smelting process. Its function is to react the oxygen in the molten pool with the deoxidizer, thereby reducing the oxygen content in the steel to improve the performance and quality of the steel. Deoxidizer is usually an alloying element added to the furnace. Common deoxidizers include aluminum, silicon, manganese, etc.
Common deoxidizer selections are determined based on factors such as specific steel grade, process requirements, and cost. For example, elements such as silicon and aluminum are commonly used in the deoxidation process of different steel types. In the steelmaking process, controlling the amount and method of adding deoxidizer is crucial to ensuring the quality of steel.
Before choosing a suitable deoxidizer, let’s first understand the main functions of the deoxidizer.
Functions of deoxidizer
The main functions of deoxidizer are as follows:
- Deoxidation: The deoxidizer reacts with the oxygen in the molten pool, reducing the oxygen into gas to reduce the oxygen content and prevent the formation of oxide inclusions.
- Improve the purity of steel: Deoxidizers can reduce the oxygen content in steel, improve the purity of steel, and help improve the mechanical and chemical properties of steel.
- Improve the uniformity of steel: By controlling the amount and method of deoxidizer added, the elements in the molten steel can be evenly distributed, thereby improving the uniformity of steel.
- Promote the formation of crystallization nuclei: The addition of deoxidizer can promote the formation of crystallization nuclei, which is beneficial to refining the grains and improving the strength and toughness of steel.
Types of steelmaking deoxidizers
Next, let’s talk about the types of steelmaking deoxidizers.
The main ferroalloys commonly used for deoxidation in steelmaking include the following:
- Ferro Silicon (FeSi): Ferro silicon is an iron alloy that usually contains 15% to 90% silicon. It is one of the most commonly used deoxidizers, which can effectively remove oxygen from steel and improve the strength and hardness of steel.
- Ferro Manganese (FeMn): Ferro Manganese is an iron alloy that usually contains 65% to 95% manganese. It is also often used as a deoxidizer, which can reduce the oxygen content in steel and improve the toughness and fatigue resistance of steel.
- Ferro Aluminum Silicon (FeAlSi): Ferro Aluminum Silicon is an iron alloy that usually contains 15% to 45% aluminum and 15% to 35% silicon. It can effectively remove oxygen and improve the corrosion resistance of steel.
- Manganese-silicon alloy (Ferro Silico Manganese, FeSiMn): Manganese-silicon alloy is an iron alloy that contains a large amount of manganese and silicon and is suitable for use in the steel smelting process with some special needs.
- Ferro Alumino Titanium (FeAlTi): Ferro Alumino Titanium is an iron alloy containing aluminum, titanium and other elements, and is suitable for deoxidation of special steel types.
The composition and content of these ferroalloys can be adjusted and selected according to specific steel types and production requirements to achieve the best deoxidation effect and steel performance.
First of all, based on my personal knowledge, these alloy materials can be used as deoxidizers to eliminate excess oxygen molecules in molten steel.
But when it comes to which one is best, the question is difficult to answer.
Because the purpose of steelmaking is to control the carbon content in the molten iron, while reducing and eliminating P, S, N, O and other harmful elements that affect the performance of steel, and to retain or increase Si, Mn, Ni, The content of elements such as Cr that improve the performance of steel allows these beneficial elements to exist in a certain proportion, thereby obtaining the best performance and steel that best meets certain needs.
It can be seen that steelmaking is a very complex process. Deoxidation is only one part of steelmaking. This part is important, but other parts are also important.
The deoxidation process, to put it bluntly, is to use some alloy materials that are easy to react with oxygen molecules to generate oxides that are easy to precipitate or have a higher melting point, thereby reducing the content of oxygen molecules in the molten 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.
Let’s take a look at how common deoxidizers deoxidize.
Ferro silicon
Due to the strong affinity between silicon and oxygen, when ferrosilicon is added to steelmaking, the following deoxidation reaction occurs:
2FeO+Si=2Fe+SiO₂
Silica is the product of deoxidation. It is lighter than molten steel. It floats on the surface of the steel and enters the slag, thereby removing the oxygen in the steel. It can significantly improve the strength, hardness and elasticity of the steel, increase the magnetic permeability of the steel, and reduce the temperature of the transformer. Hysteresis loss in steel.
Silicon manganese
The oxygen in molten steel is actually FeO, which is produced by the reaction between red-hot Fe and pure oxygen at high temperatures.
After adding silicon-manganese alloy to the molten steel, Si + 2FeO = SiO2 + 2Fe Mn + 2FeO = MnO2 + 2Fe
The generated SiO2 and MnO2 react with CaO to form slag and are removed, thereby achieving the purpose of deoxidation.
In addition, adding silicon-manganese alloy also has the effect of adjusting the composition of steel, that is, adjusting the content of silicon and manganese in the steel.
Silicon and manganese in silicomanganese alloys have a strong affinity with oxygen. When silicomanganese alloys are used in steelmaking, the deoxidation products MnSiO3 and MnSiO4 are produced to melt at 1270°C and 1327°C respectively. They have low melting points, large particles, and are easy to float. , good deoxidation effect and other advantages.
Under the same conditions, using manganese or silicon alone for deoxidation, the burning loss rates are 46% and 37% respectively, while using silicon-manganese alloy for deoxidation, the burning loss rate is 29%.
Ferromanganese
Manganese can strengthen ferrite and refine pearlite, so it can improve the strength and hardenability of steel, so it can be used as an alloying element of steel. The strength limit of steel increases with the increase of manganese content (≤7%). For every 1% increase in manganese content, the strength limit increases by 98066.5kPa, and the plasticity limit of steel also increases accordingly. When the manganese content in steel is greater than 10%, the steel’s corrosion resistance in the atmosphere is greatly enhanced. Manganese can also reduce the harm of oxygen and sulfur to steel, thereby improving the forgeability and rollability of steel. Although manganese was discovered as early as 1774, its important role in the steel industry was not recognized until the invention of the bottom-blown acid converter in 1856 and the invention of the open-hearth steelmaking method in 1864. Now manganese has become an indispensable and important raw material for the steel industry.
Manganese is a highly active metal, and its chemical properties are more active than iron. When manganese is added to molten steel, it can react with FeO to form oxide slag that is insoluble in the molten steel, floating on the surface of the molten steel, reducing the oxygen content in the steel. FeO+Mn→Fe+MnO The deoxidizing ability of manganese in molten steel should be said to be relatively low compared with some other elements (such as calcium, aluminum, silicon), but because it is easy to produce and the price is relatively low, it is still popular among steel companies. Especially for making boiling steel, the use of ferromanganese alloy for deoxidation is an ideal deoxidizer. Since manganese has a weak deoxidizing ability, ferromanganese alloy can adjust the oxygen content of steel without deoxidizing it. Too much to boil. At the same time, the presence of manganese can also enhance the deoxidation ability of silicon and aluminum, because the deoxidation product MnO and other oxides (such as Si02) can form low melting point compounds, which are beneficial to be eliminated from the molten steel.
Although the deoxidation principles of the above three steelmaking deoxidizers are roughly the same, due to different alloy compositions and contents, the contents of some beneficial elements in the molten steel are different, which can also be understood as the steel produced is different and has different properties.
Therefore, in my personal opinion, one cannot simply tell which deoxidizer is better. Instead, it is necessary to decide which deoxidizer is more suitable based on the properties of the steel being made.
