During the alloying process, the yield of alloying elements is not a fixed value, but is relatively stable within a range, and within this range, the yield of alloying elements can be high or low. The main factors affecting the yield are:
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Molten steel temperature
As the temperature of molten steel increases, the free energy of alloying elements dissolved in molten steel decreases, which is conducive to the dissolution of alloying elements. The free energy of oxide formation of alloying elements reacting with oxygen generally increases with the increase of temperature, that is, the increase in temperature is not conducive to the oxidation reaction of each alloying element, but reduces their oxidation loss in the furnace gas or furnace pool, thereby increasing the yield. However, the situation of silicon powder used for indirect deoxidation is just the opposite. This is because as the temperature increases, the deoxidation ability of the element weakens. Therefore, at higher temperatures, the amount of silicon powder consumed to achieve the same deoxidation purpose increases, which reduces the yield of silicon.
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Steel specifications and composition
The specifications and composition of steel directly affect the yield of alloying elements. For example, carbon determines the oxygen in steel, so it is easier to deoxidize high carbon steel than low carbon steel. When the same amount of silicon or manganese is added for deoxidation, the recovery rate of silicon or manganese in high carbon steel is higher than that in low carbon steel. For another example, a large amount of Mn, Cr, and Mo in the molten steel will increase the recovery rate of nitrogen. For easily oxidized elements such as Al and Ti, the higher the content of the element in the steel grade specification, the higher the recovery rate.
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Physical and chemical state of slag
The physical and chemical state of slag also has a great influence on the recovery rate of alloy elements, especially the viscosity and basicity of slag. For example, after some alloy elements with a density smaller than that of molten steel are added to the molten pool, they float between the rolling steel interfaces. If the alloy block is large and the slag viscosity is too large, it will be unfavorable for the rapid dissolution of alloy elements in the molten steel, which will cause increased burning loss. There are also some alloy elements whose affinity with oxygen is greater than that of silicon. After being added to the furnace, they will cause the reduction of silicon in the slag (SiO2), such as aluminum or titanium. However, when the slag basicity is high, the activity of (SiO2) in the slag decreases, and the reduction of silicon is poor. Therefore, when smelting aluminum steel or titanium steel, in order to reduce the burning loss of aluminum or titanium, improve the yield and control the large amount of silicon increase in molten steel, all or part of the slag is often removed before adding aluminum or titanium, and slag with higher basicity must be made at the same time.
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Physical and chemical properties of alloying elements
In the molten pool, the yield of alloying elements is related to various physical and chemical properties of the elements, such as the solubility of the elements in molten steel, the density and melting point of the alloy, the boiling point of the elements and the deoxidation ability. In steel, although these properties have a universal and comprehensive influence on the yield of alloying elements, for different alloying elements, only one or two factors may be the main ones. Without considering the influence of other factors, the stronger the solubility of the alloying element in molten steel, the higher the yield; and the weaker the solubility, the lower the yield. The higher the density of the alloy and the molten steel; on the contrary, the yield is also affected. The influence of the boiling point of the elements is more obvious. Generally, the elements that are gaseous at the steelmaking temperature have a generally low yield. The stronger the deoxidation ability of the alloying element, the lower the yield; the weaker the deoxidation ability, the higher the yield; and the elements without deoxidation ability have the highest yield.
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The degree of deoxidation of the molten steel
The better the deoxidation of the molten steel, the less the oxidation loss of the alloying elements, and the higher the yield.
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The time, size and method of adding alloying elements
The time, size and processing method of adding alloying elements also have a great influence on the yield. If added too early, the more active and easily oxidizable elements will burn out more and the yield is low. The yield of adding alloying elements in block form is higher than that of adding alloying elements in powder form. The yield of alloying elements added to the steel, on the slag surface, or in the steel flow and ladle is slightly different.
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The operation level of the steelmaker
Electric furnace steelmakers should analyze specific situations based on given yields. Only in this way can they accurately control the chemical composition of the molten steel.
