Brief discussion on current iron smelting operation process of branch plant

　　Abstract: with the rapid development of stainless steel production in the world, China's market demand for stainless steel materials is also growing. At present, most of them need to be imported. Therefore, in recent years, China's stainless steel production enterprises have increased more. How to plan and design the adopted production process and equipment for these enterprises, so as to make the products of high quality, low production cost and competitive in the market after the project is put into operation, is a problem that designers must first consider. Converter is a commonly used furnace for stainless steel refining, and our company (refining branch) uses the converter refining method to smelt 201, 304 and other steel grades.

　　Key words: stainless steel refining converter smelting

　　1. Prospects

　　The development of stainless steel production in our refining branch is the need of the market, but what is stainless steel? Why is there so much demand for stainless steel in the current market? What is his use? First of all, stainless steel is the abbreviation of stainless and acid resistant steel. It is called stainless steel for its resistance to air, steam, water and other weak corrosive media or stainless steel. Second, with the development of people's growing material civilization, stainless steel can no longer meet the supply demand of the current market. Then, stainless steel has good corrosion resistance, oxidation resistance, processability, wear resistance and beautiful decorative appearance, It is widely used in chemical industry, petroleum, aerospace, energy, light industry, textile, building decoration, medical equipment, kitchen and tableware and other sectors of the national economy. With the progress of science and technology, the development of national economy and the improvement of people's living standards, the application field of stainless steel will be continuously expanded.

　　2. Refining

　　The premise of refining in the branch plant must be molten iron. The main source of molten iron is the initial smelting in the electric arc furnace, blast furnace and medium frequency furnace, which is mixed into the AOD furnace for refining. The main purpose of refining is to remove C, P and S. for 304 steel, c<0.05, p<0.042 and s<0.01 are required. The AOD refining in our refining branch plant can fully meet this requirement. Our refining principle is to blow different proportions of O2 and N2 mixed gas into the molten pool, O2 blowing causes O2 + c-co in molten steel to reduce carbon; The blowing of N2 as an inert gas can dilute the co bubbles rising in the molten steel, thus reducing the co partial pressure, making the smelting balance conducive to the above reactions and inhibiting the o+cr-cr2o3 reaction, so as to achieve the purpose of decarburization and chromium preservation.

　　3. Converter

　　There are many types of stainless steel refining furnaces, including AOD, clu, mrp-l, k-obm-s/k-bop, kms-s, g0r, etc; The vacuum type includes VOD, ss-vod, VODC, RH-OB, RH-KTB, etc. The type adopted by the refinery of the company is the AOD converter, which is a cylindrical furnace with 6-7 air guns and a furnace mouth, which can rotate 180 °. Under normal smelting conditions, oxygen or inert gas is blown into the solution pool through 6 air gun pipes for oxidation and reduction. The furnace body can be used for feeding, slag discharging and steel discharging, and the operation is simple and flexible. The AOD Process technology system used in AOD furnace 2.4.6 is provided by Praxair company. The smelting essence of Praxair is that temperature = time = money. This system is easy to operate, automatic and has accurate data on the temperature and composition of the solution pool. Converter is a main production equipment in stainless steel production. Recently, newly-built stainless steel manufacturers mostly adopt converter / vacuum composite refining process, and the converter types used are different. Therefore, when new stainless steel smelting projects are built, multiple schemes should be compared to accurately select the converter type for refining. AOD, clu, K-OBM-S, mrp-l and GOR converters are common converters for refining at present. They have different characteristics. The designer shall select the type of converter according to the initial conditions such as the scale of the project, product scheme, raw material composition and price, and the matching with the next continuous casting, so as to achieve the effect of high quality, high efficiency, flexibility, low consumption and low cost after the project is put into operation. AOD converter with top gun and intelligent refining system has the functions of complete decarburization and complete reduction. It can not only adapt to the two-step process operation as a single refining converter, but also cooperate with VOD to form a converter / vacuum composite refining process for three-step operation. It has flexible production means and strong adaptability to various conditions. At present, it is still the preferred furnace type for stainless steel production.

　　4. Smelting

　　The smelting method adopted by the branch plant is "three-step decarburization". In the early stage, six side guns and top guns of the converter are used to blow in O2 and add enough Cao for combustion and temperature rise c+o2-co2. In the middle stage, casio4 in the solution pool is stripped off with other P and s compound slags. As a large amount of heat is taken away from the slags, enough Cao is added again to continue heating. When the temperature of the solution pool reaches 1690-1710 ℃, the last Cao is added for micro decarburization, During the smelting process, the precise composition control shall be carried out according to the steel type to keep the molten steel in good white slag and fluidity. During the smelting process, due to the unstable operation of technical workers, it is inevitable to have hidden dangers such as slag spraying, which is easy to cause instability of steel water volume and great deviation of later composition. Therefore, slag spraying should be avoided as far as possible during the smelting process.

　　5. Conclusion

　　With the continuous development and progress of China's science and technology, the demand of the stainless steel market has been increasing rapidly, the Chinese stainless steel enterprises have also been growing, and the required equipment and smelting level are also improving day by day. We should adhere to the scientific concept of development and the path of sustainable development, and create and design a more perfect smelting process scheme with the advantages of low cost, high quality and no pollution in the field of stainless steel smelting, Meet the growth and development of the enterprise.