Analysis of the advantages and disadvantages of the three smelting processes of Chinese stainless steel
At present, China, as a major producer and consumer of stainless steel, has a wide variety of stainless steels. Different smelting process routes have been formed according to the different uses of steel types and raw materials. In recent years, China's stainless steel smelting technology has developed in the direction of improving productivity, simplifying processes, reducing production costs and improving molten steel quality, and has been continuously optimized in terms of raw materials and process equipment. The three smelting processes have their own advantages and disadvantages: At present, the smelting process for producing stainless steel in the world is mainly divided into one-step method, two-step method and three-step method, in which the two-step method of EAF + AOD (electric arc furnace + argon oxygen refining furnace) accounts for about 70%, and the three-step method is about 20%. As low-phosphorus molten iron is widely used in stainless steel production, the new one-step stainless steel smelting process has also been adopted by more and more stainless steel production enterprises. In order to adapt to the fierce competition in the stainless steel market, improve product quality and reduce production costs, Chinese enterprises should choose the appropriate stainless steel smelting process according to their actual situation. One-step stainless steel smelting process. The early one-step stainless steel smelting process refers to the process of melting, decarburizing, reducing and refining scrap steel in an electric furnace, smelting the charge into stainless steel in one step. With the continuous development of the refining process outside the furnace and the wide application of the AOD furnace in the field of stainless steel production, this one-step smelting production process using only an electric furnace to smelt stainless steel has been phased out due to the long smelting cycle, low operating rate, and high production cost. At present, many stainless steel production enterprises use some low-phosphorus or dephosphorized hot metal instead of scrap steel, and use hot metal and alloy as raw materials to enter the AOD furnace for stainless steel smelting, thus forming a new one-step smelting process. Compared with the earlier one-step smelting process, the new one-step smelting process eliminates the electric furnace smelting link in the production process. Its advantages include: first, lower investment; second, lower production costs; third, blast furnace molten iron smelting reduces the cost of ingredients and reduces energy Consumption, which improves the purity of molten steel; the fourth is that the scrap ratio is low, adapting to the existing scrap market; the fifth is that it is particularly economical for smelting 400 series stainless steel. However, the new one-step method has certain requirements on raw material conditions and product schemes: First, the phosphorus content of the molten iron in the AOD into the furnace is less than 0.03%, so the molten steel dephosphorization process must be added; second, it is not suitable for complex ingredients and alloys High-content stainless steel varieties. The new one-step stainless steel production process is currently widely used to produce 400 series stainless steel. As a developing country, China lacks scrap resources and is extremely poor in nickel. In addition, the application range of 400 series stainless steel in daily life and industrial production is becoming wider and wider. These objective conditions have made the new one-step stainless steel smelting more and more. The more production companies adopt it. Two-step stainless steel smelting process. The representative process routes of the two-step stainless steel are EAF → AOD, EAF → VOD (electric arc furnace → VOD vacuum refining furnace). The capacity of the EAF → AOD process currently accounts for about 70% of the world ’s stainless steel capacity. The EAF furnace is mainly used to melt scrap steel and alloy raw materials to produce stainless steel premelts. The stainless steel premelts are then smelted into qualified stainless steel molten steel in the AOD furnace. . The two-step stainless steel smelting process is widely used in the production of various series of stainless steel. Its advantages include: the electric furnace does not require high raw materials, the production cycle is slightly shorter than the one-step process, and the flexibility is good. It can produce ultra-low carbon and nitrogen stainless steel. 95% stainless steel varieties. However, the two-step method still needs to pay attention to the following three points in terms of medium consumption and variety schemes. First, with the progress of the smelting process and the improvement of the operation level in recent years, the consumption of argon and other media in the two-step smelting process has been significantly reduced. However, compared with the one-step method and the three-step method, the consumption of argon and other media is still slightly larger; the second is that when the AOD furnace decarburization reaches the end, the oxygen content in the molten steel is high, and the ferrosilicon must be added to reduce the oxygen in the molten steel, so the ferrosilicon consumption The amount is high; the third is that it can not be used to produce ultra-low carbon, nitrogen stainless steel, and the gas content in the steel is relatively high. Three-step stainless steel smelting process. The basic process flow of the three-step method is: preliminary refining furnace → re-blowing converter / AOD furnace → vacuum refining device. The three-step method is an advanced method for smelting stainless steel. The product quality is good. It is suitable for professional manufacturers and also for stainless steel production of joint steel companies. The three-step stainless steel method adds a deep decarburization link on the basis of the two-step method. Its advantages of the smelting process are: first, the division of labor in each link is clear, the production rhythm is fast, and the operation is optimized; second, the product quality is high, nitrogen, hydrogen, The content of oxygen and inclusions is low, and the range of varieties that can be produced is wide; third, it can be smelted with hot metal, and the requirements for raw materials are not high, and the choice of raw materials is flexible. However, the three-step stainless steel smelting process realizes the metallurgical function step by step, which will have the following impact on production investment: first, the process link is increased, and the investment and production costs are higher; second, the vacuum equipment system is complicated and the maintenance amount is large. The process choice of the joint steel enterprise is more flexible: Factors such as raw material conditions, production scale, product schemes, operating costs, and workers' operating habits of stainless steel manufacturing enterprises all affect the choice of stainless steel smelting production processes. Due to factors such as raw materials, operating costs and product schemes, which are greatly affected by market fluctuations, the selection of production processes for modern stainless steel smelting workshops should have some flexibility, and the production processes and product schemes can be adjusted according to market conditions. Most of China's large-scale stainless steel production enterprises are joint steel enterprises, such as Taigang, Jiugang and Baosteel, all of which produce both stainless steel and carbon steel. For these joint steel companies, the range of raw materials is relatively wide, with sufficient supply of hot metal and scrap steel that can meet the needs. These companies have greater flexibility in the selection of stainless steel smelting process routes. TISCO stainless steel smelting process. TISCO has three stainless steel smelting workshops, namely the third steelmaking plant, the southern area of ​​the second steelmaking plant and the northern area of ​​the second steelmaking plant. The smelting process adopted by the third steelmaking plant is: EAF → AOD, which mainly produces duplex stainless steel, heat-resistant steel, high alloy stainless steel and high value-added stainless steel. The smelting process used in the southern area of ​​the second steelmaking plant is: hot metal pretreatment → K-OBM-S furnace → VOD → LF furnace, which is mainly used to produce ferritic and martensitic stainless steel. The smelting process used in the northern area of ​​the second steelmaking plant is: dephosphorization converter → AOD → LF furnace / VOD and electric furnace → AOD → LF / VOD. The northern area of ​​the second steelmaking plant has a flexible process path that can adopt a new one-step method It is also possible to produce stainless steel using the two-step method and the three-step method. Jiugang stainless steel smelting process. The smelting production process configuration of Jiu Steel's stainless steel workshop is as follows: 1 molten iron top spray dephosphorization station, 1 dephosphorization converter, 1 EAF, 2 AOD, and 2 LF refining furnaces. Its products cover a wide range, including 200 series, 300 series and 400 series stainless steel. Jiugang's stainless steel workshop mainly adopts the following two processes for stainless steel smelting: Process one is the top spray dephosphorization of molten iron tank → EAF → AOD → LF, which is a two-step production process, mainly used to produce 200 series and 300 series stainless steel; The second process is dephosphorization converter → AOD → LF, which is a new one-step production process, which is mainly used to produce some steel grades of 400 series. Smelting process of Baosteel Stainless Steel Branch. The stainless steel production process configuration of Baosteel Stainless Steel Branch is: 2 hot metal spray top dephosphorization stations, 2 120tEAF, 2 135tAOD, 1 LTS processing station and 1 120tVOD. The technological process adopted by Baosteel Stainless Steel Branch is relatively diversified. Process 1: Dephosphorization of molten iron top spray → EAF → AOD → LTS processing station / VOD, production of 200 series, 300 series and 400 series stainless steel; Process 2: Dephosphorization of molten iron top spray → AOD → VOD, production of 200 series and 400 Some steel grades of the system; Process 3: Electric furnace → AOD → LTS processing station / VOD, producing 200 series, 300 series and 400 series stainless steel. From the above comparative analysis, China's large-scale stainless steel production enterprises adopt the new one-step method and two-step method as the main process flow for stainless steel production. Only when producing ultra-low carbon, nitrogen and other high-quality stainless steels, the three-step process flow is used. Choose process route according to local conditions The determination of the stainless steel smelting process should first be based on the product outline, based on the stainless steel smelting raw material composition and stainless steel refining mechanism, and select the appropriate stainless steel smelting process. For large-scale stainless steel production enterprises, the configuration of workshop process equipment should be able to meet the requirements of diversified process routes to meet the needs of large fluctuations in raw material prices, and timely update and select the best raw material ratio scheme, while smelting equipment should be able to meet different needs Smelting process of raw material proportioning. Due to the lack of stainless steel scrap resources in China, the high cost of ingredients in the stainless steel smelting process with scrap as the main raw material, coupled with the high energy consumption of all scrap steel smelting, and the poor quality of the scrap steel brings many harmful elements into the molten steel. Manufacturers tend to use dephosphorized blast furnace molten iron to smelt stainless steel. In particular, iron and steel joint enterprises, using the carbon steel system blast furnace to supply part of the molten iron to the stainless steel smelting system, can effectively reduce the cost of raw materials per ton of steel. At the same time, dephosphorization treatment facilities are commonly used in stainless steel production processes. The application of dephosphorization treatment facilities can not only reduce the raw material requirements for stainless steel production, but also reduce production costs, so that blast furnace molten iron, ordinary scrap steel, high phosphorus pig iron and high phosphorus alloys can be used in large quantities for stainless steel production.
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