Introduction
In steelmaking production, refractory materials are generally used in furnace linings and tundish, which are called steel packages. The steel packaging is mainly used for deoxidation and purification of molten steel, and inclusions are removed from molten steel. During the melting process, phosphorus enters the molten steel system from the refractory materials used for steel packaging, resulting in return phosphorus of refined molten steel. Reducing back phosphorus has become a key issue for modern steelmaking.
The sources and types of phosphorus
The main sources of return phosphorus are mainly due to the phosphorus contained in refractory materials during steelmaking and insufficient deoxidation during smelting. The types of phosphorus returned in steelmaking can be divided into four categories: loose sulfur, silicate sulfur, free manganese sulfide and complex phosphide. From the point of view of flame dephosphorization, when the silicon content of molten steel is relatively high, the return phosphorus is mainly loose sulphur phosphorus. In the case of low silicon content and the addition of high manganese, the return phosphorus in steel mainly comes from manganese sulfide. In order to reduce the return phosphorus, it is necessary to reduce the phosphorus content of refractory materials used as steel packaging and properly increase the deoxidation conditions during refining.
The causes of return phosphorus
The reasons for the return phosphorus of molten steel are mainly due to the poor match between the materials of the steel packaging and the slag system, and the poor sealing performance between the steel packaging and the furnace lining, resulting in phosphorus-containing slag entering the steel system from the steel packaging. In addition, improper selection of steel package refractory materials or raw materials and loose control during smelting will cause the steel system to return phosphorus and cause serious consequences such as poor cleanliness of molten steel and poor quality of castings.
Methods of preventing and reducing return phosphorus
1. Selection of high-quality steel package refractories. The selection of high-quality steel package refractories has always been a measure to prevent the return of phosphorus. High-quality refractory materials can reduce the amount of phosphorus entering the molten steel and reduce the return of phosphorus.
2. Improve the slag-steel package match. The match between the materials of the steel package and the slag system is an important factor affecting the return of phosphorus. Use slag systems with good compatibilities such as calcium aluminate-calcium fluoride-basic slag systems to reduce the return of phosphorus.
3. Increase the slag cover rate of the steel package surface. Control the level of molten steel, arrange foaming and slag, and increase the slag covering rate of the surface of the steel package during smelting, so that the molten steel is fully separated from the steel packaging material and play a role in preventing return phosphorus.
4. Improve the sealing of steel packages and furnace linings. Reasonable selection of steel package size and shape, reasonable arrangement of pushing blocks and flaps, strict implementation of furnace lining sealing measures and reasonable selection of furnace lining materials are all effective measures to improve the sealing performance between steel packaging and furnace lining and prevent slag intrusion.
Conclusion
Return phosphorus is an important factor that affects the quality of molten steel in steelmaking. If the return phosphorus cannot be effectively prevented and reduced, it will directly increase production costs, reduce the quality of castings, and even cause environmental pollution. Therefore, it is necessary to prevent and reduce return phosphorus. This can be done by selecting high-quality steel package refractories, improving the slag-steel package match, increasing the slag cover rate of the steel package surface, and improving the sealing of steel packages and furnace linings.
