Phosphorus is one of the most harmful elements in steel, especially in stainless steel, which not only intensifies the segregation of stainless steel components, but also has a very adverse effect on the point corrosion resistance, stress corrosion resistance and welding performance of stainless steel. Reducing the phosphorus content in stainless steel has always been a concern of metallurgical workers. Until now, this problem has not been well solved and remains the largest research topic in refining technology. At present, stainless steel smelting mainly uses arc furnace return oxygen blowing method and furnace refining method. The steel material is recycled again and again, so that the phosphorus in the steel is more and more enriched. Coupled with the addition of ferrochrome and other phosphorus, it is easy to appear that the phosphorus content of liquid steel exceeds the standard phenomenon. Therefore, the dephosphorization of stainless steel is becoming more and more prominent.

Research and development of stainless steel dephosphorization technology can be broadly divided into two categories, that is, oxidation dephosphorization and reduction dephosphorization. The oxidative dephosphorization process requires BaO or CaO based alkaline slag, while the reduction dephosphorization requires Ca or calcium alloy. Regardless of the route, the core issue is to maximize the removal of phosphorus from the steel while preserving chromium. However, because the alloy steel required by modern industry contains very high alloy components, such as chromium, manganese, etc., if the oxidation method is used to dephosphorize such high alloy steel, a large number of alloying elements will be oxidized away while dephosphorizing; On the other hand, phosphorus in iron alloys has always been difficult to remove, especially those produced under reduction conditions, and in recent years, the production of low phosphorus steel and ultra-low phosphorus steel has become more and more stringent requirements for phosphorus content in iron alloys. Therefore, people hope to develop an effective dephosphorization method under reducing conditions to achieve the purpose of chromium preservation and dephosphorization. In the process of steelmaking, phosphorus in molten steel enters the slag in two ways, that is, oxidation and reduction dephosphorization. When the oxygen potential of the system is lower than the critical value, phosphorus will enter the slag mainly in the form of P3- (reduction and dephosphorization), and the lower the oxygen potential of the system, the easier the process is to carry out. People most commonly used to do reduction dephosphorization agents are calcium metal and calcium alloys (including calcium carbide, calcium silicon alloy), in addition to aluminum-magnesium, calcium-aluminum alloy.

The experiment shows that dephosphorization with calcium-base slag system in reductive atmosphere can achieve this goal. Moreover, the reduction dephosphorization method can make iron and steel enterprises use soft iron and return materials with high phosphorus content and low price as raw materials, and greatly improve the yield of alloy, thus reducing the cost of steelmaking. Therefore, reduction dephosphorization method has more research significance and economic value.

The dephosphorization rate is closely related to the carbon content of molten steel. For example, when dephosphorization with Ca, high carbon will promote the reaction, thus rapidly consuming calcium metal, resulting in a reduction in the dephosphorization rate. When CaC2 is used as a dephosphorization agent, if the carbon is high, the decomposition of CaC2 will be insufficient, reducing the decomposition of calcium metal, affecting the effect of dephosphorization. Therefore, the low carbon content in the liquid steel can accelerate the dephosphorization reaction. The effect of oxygen content in steel on dephosphorization must also be considered during reduction and dephosphorization, because oxygen in steel directly affects the utilization rate of (Ca). The conditions for obtaining >50% are: aC<0.92 and aO<4×10-4. In theory, chromium in reduction and dephosphorization does not calcify with metal and does not participate in the reaction, so there should be no loss of chromium in liquid steel. But in fact, the chromium content will affect the dephosphorization rate. The results show that the influence of chromium content on the dephosphorization rate is due to its influence on carbon activity. When dephosphorizing metal calcium, the lower the temperature, the higher the dephosphorization rate. When CaC2 is used for dephosphorization, the dephosphorization rate is fast at high temperature and opposite at low temperature. However, from the overall results, the temperature has little effect on the dephosphorization rate. Therefore, in actual production, taking into account the total economic benefits, there is generally no special requirement for temperature (except for pure calcium dephosphorization). It is found that the dephosphorization with graphite carburization can hardly be done under the same experimental conditions. With Al2O3 crucible, the dephosphorization rate is low; The dephosphorization rate is higher in MgO, CaO and dolomite crucible. As a flux, CaF2 is not only cheap, but also has a low melting point, which is easy to form a low melting point compound with other components and is convenient for slagging. Can dissolve dephosphorizing agent Ca, CaC2, reduce the vapor pressure of calcium, reduce its volatilization loss; It can reduce the activity of calcium phosphide and promote the dephosphorization reaction, so it is widely used. However, in the process of dephosphorization by powder spraying, the effect of CaF2 in the slag is not obvious due to the good kinetic conditions and the increase of the reaction surface.

With the recycling of scrap steel, the phosphorus in steel is increasing because it cannot be effectively removed by oxidation, resulting in the phosphorus content of some stainless steel return materials on the market as high as 0.047 ~ 0.087%. Therefore, in-depth research, improvement and development of stainless steel dephosphorization methods has become an increasingly urgent problem.

Although the reduction dephosphorization method has defects that the dephosphorization products are difficult to deal with, easy to pollute the environment, complex processes before and after and high requirements for equipment, but because the reduction dephosphorization method does not lose expensive alloying elements (such as Cr,Mn, etc.), and the dephosphorization rate is high, the reduction dephosphorization method can make iron and steel enterprises use soft iron with high phosphorus content and low price and return material as raw materials. And greatly improve the yield of the alloy, thereby reducing the cost of steelmaking. Therefore, reduction dephosphorization method has more research significance and economic value.