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Innovation in the world electrical steel process

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  More than 100 years of history in the production of electrical steel is also a history of continuous innovation. The transfer of hot-rolled silicon steel sheets to cold-rolled electrical steel strips is the first major technological change. After the cold rolling process, with the development of oriented electrical steel, different The emergence of inhibitors and technological advances in pre-process smelting and casting, the continuous innovation of process flow in the pre-process, and the simplification and continuation of the post-process process.
  The pre-process is from smelting to hot rolling; the hot rolling coil is transported to the electrical steel mill through different processes until the finished product is called the post-process. The most revolutionary in these processes is the pre-process, from steelmaking refining to the production of hot rolled coils, which are characterized by thinning slabs and shortening processes. After the process, regardless of orientation and non-oriented steel, try to take a rolling process to achieve the thickness of the product, eliminating the intermediate annealing, and then the acid-rolled continuous production (CDCM) of the non-oriented steel.
  The semi-process variety in the traditional process is still popular in the West. It is a large-scale non-oriented variety. It is produced in an automobile board production plant. It is a low-carbon steel, low-cost, and its final annealing and surface blue is in iron. The core manufacturer completed. This product was successfully developed in the 1980s by the former WISCO, and it was once a Chinese and foreign
  Down to the main material of the B09 version of the joint venture refrigerator compressor and motor, but the rapid development of cold-rolled full-process electrical steel (non-oriented steel), the cost gradually reduced, and thus, the semi-process gradually withdrew from the market. There are thousands of small and medium-sized motor manufacturers in China. Due to the small scale of production, dispersion and diversified core size, it is impossible to organize intensive production. This is also an important reason why the promotion of semi-process products in China is not open. As far as the semi-process product itself is concerned, the iron core produced according to the process requirements is the most fully utilized magnetic material of the material itself, and is an energy-saving product.
  1 plate belt production process evolution
  1.1 Process 1: Die Casting - Initial Rolling - Hot Rolling
  There are still a few factory applications for this process. The general orientation steel production process of the Arrigani plant in Pittsburgh, USA, is obtained by hot rolling a slab from a die casting to a coil by preliminary rolling. The original CJ7411 contract signed by WISCO in 1974, two of which are high-grade non-oriented steel and HiB steel. The slab is obtained after initial casting by die casting. In the 1980s, WISCO made a large number of equipment matching and process innovation work to change the mold blank to the continuous casting billet.
  1.2 Process 2: slab continuous casting and rolling - conventional production process
  This process, ie slab continuous casting (slab thickness 180-250mm), is the main production process for all varieties at home and abroad.
  1.3 Process 3: Thin slab continuous casting and rolling production process
  The process is thin slab continuous casting (CSP, blank thickness 70-90mm), and the development and production of electrical steel at home and abroad have achieved results. So far, the production of non-oriented medium and low grades has become normal. It has been confirmed in magnetics that it is possible to produce oriented electrical steels of all specifications and grades. However, surface defects such as iron indentation, slag entrapment, and furnace roll scratching have become major problems that restrict the production of oriented electrical steel in large quantities.
  1.4 Process 4: Thin Strip Continuous Casting - Near-End Forming Production Process (Electrical Steel, Duplex Stainless Steel, Cold Rolled AHSS, Aluminum Alloy)
  Thin strip continuous casting - near-final production process is the most advanced process, originated from the US Nucor company, has been industrialized, China Baosteel has been developed for a long time, now Ningbo steel mill, but mainly produces carbon steel, production is not yet stable. Shagang decided to introduce Nucor's technology and equipment, each with a capacity of 500,000 tons, but mainly produced carbon steel. Although the production of electrical steel by thin strip casting has been developed for many years, the breakthrough is that the research team of the State Key Laboratory of Rolling Steel of Northeastern University after 2008 has made significant progress in the production process and variety development of electrical steel, and it is possible to make a hundred years of electrician production. Steel's process technology has revolutionized the subversive.
  1.4.1 Comparison of basic parameters of Castrip and thin slab continuous casting and thick slab continuous casting
  In the process of forming different slab thicknesses, the solidification time is different due to the different cooling rates, thus affecting the internal structure of the slab, and finally the performance of the finished product varies widely. The basic casting parameters of Castrip and thin slab continuous casting and thick slab continuous casting are shown in Table 1.
  1.4.2 Comparison of investment, cost and energy consumption of thin slab continuous casting and thin strip casting and rolling
  Advantages of thin strip continuous casting process: green, environmental protection, low cost, of which the length of production line: thick slab continuous casting is more than 600m, thin slab continuous casting is about 400m, thin strip casting is less than 60m. A comparison of investment, cost and energy consumption in thin slab continuous casting and thin strip casting is shown in Figure 1.
  Evolution and Mechanism Analysis of 2 Oriented Electrical Steel Process
  The history of the development of electrical steel is essentially a history of steelmaking technology and the development of metallographic, gold, metal heat treatment and analytical testing technology, steelmaking equipment technology
  The improvement of the technology has made it possible to improve the precision of smelting ultra-pure steel and trace elements. The improvement of detection means has a scientific basis for profoundly understanding the influence of various factors on the final magnetism and the innovative and rational process. Under the above premise conditions, it is possible to produce advanced non-oriented steel. Deep understanding of the composition requirements, inhibitors, texture evolution of the production of oriented steel in the whole process, pointed out the direction for us to improve the magnetic level of oriented steel. Since the discovery of the Goss texture, scientists around the world engaged in electrical steel research have focused on the relationship between inhibitor selection, evolution, and final Goss texture.
  2.1 The role of each step in the thick slab continuous casting process with AlN as the main inhibitor (slab high temperature heating + one cold rolling method)
  In the early stage, MnS was used as the inhibitor for thick slab continuous casting process (slab high temperature heating + secondary cold rolling method) to produce silicon steel. Later, the thick slab continuous casting process with AlN as the main inhibitor and the effect of each process are shown in Fig. 2. Shown.
  The process can obtain good magnetic properties under the controlled conditions of various factors. Nippon Steel is using this process to produce the world's top high magnetic induction oriented electrical steel named HiB, and is proud of it. In order to reduce the shortcomings caused by the heating of slab 1400 °C, Nippon Steel has done a lot of work, such as slab heating in ordinary furnace to 1200 ° C, after entering the furnace into the vertical slab induction heating furnace, the temperature reaches 1400 ° C, due to The temperature of the slab entering the furnace is as high as 1050 °C, and it rises to 1400 °C. It only takes 40 minutes and the temperature is kept for 15 minutes. The total time of one cycle of the furnace is 55 minutes. Therefore, the residence time of the slab in the high temperature section is greatly shortened, and nitrogen protection is adopted. The slag is reduced, the life of the furnace is prolonged, the surface defects of the slab are also improved, and the finished product rate is improved. This process has been used by the Nippon Steel Hiroyaki Plant. When the original WISCO was introduced, it also used this process to produce general oriented steel and high magnetic induction oriented electrical steel. So far, the hot rolling three branch factory still uses this process. In 2008, a slab induction heating vertical furnace was added, but the use was not ideal. The process has a total of 14 processes, of which 8 processes are followed by 6 processes in the previous process.
  2.2 The role of each step of the thick slab continuous casting process with Cu2S+AlN as the inhibitor (slab medium temperature heating + secondary cold rolling method)
  The advantage of reducing the slab heating temperature is to prevent the generation of liquid slag, reduce the furnace shutdown time, improve the yield and energy saving; reduce the unnecessary coarse grains in the slab; it may cancel the reheating compared with the traditional process. Pre-rolling.
  Due to the advantages of reducing slab heating and great economic benefits, electric steel workers from all over the world have done a lot of work on how to reduce the slab heating temperature. The first achievement is the former Soviet metallurgical workers, using its original Cu2S+AlN. As an inhibitor. The slab heating temperature is lowered to 1280-1320 °C, and the second process is still used in the latter process. At the same time, the other processes are adjusted accordingly, and the high-quality general oriented electrical steel P17/50≤1.2W/kg is industrially produced. B8 ≥ 1.88T.
  The process was first used in China's WISCO in 2002-2004, and the steel grade was named QRD. According to this process, a professional manufacturer of general oriented steel with an annual output of 160,000 tons was built. Because this process control factor is relatively easy and stable, it The magnetic level is also at a stable high level. 0.30mm thick P17/50 is 1.05-1.2W/kg, B8=1.88-1.90T. If the composition and process are optimized, the magnetic lifting has certain potential, such as laser scoring, 0.30mm thick P17/50 reaches 1.0W. /kg is entirely possible. At present, most of the private steel produced by private enterprises are mainly based on this process.
  2.3 AlN as the main inhibitor Thick slab process after low temperature heating process and the role of each process (primary cold rolling method)
  Since 1989, Japan's Nippon Steel Hachiman Steel has developed slab low-temperature heating (1100-1150 °C), called SL steel, whose magnetic level and iron loss are comparable to HiB steel, B8 is slightly inferior to HiB steel. 1.89-1.91T or so. The reason for the decrease in the temperature of the slab is to reduce the MnS as an inhibitor, and to mainly use AlN, and the AlN portion thereof is derived from steelmaking and is precipitated at a high temperature in a post-process to precipitate dispersed particles. In addition, the steel strip is subjected to primary recrystallization decarburization annealing and then subjected to nitriding treatment at 750 ° C (or 900 ° C) to form (Si, Al) N in the steel strip, in a high temperature box furnace (hood furnace or ring furnace) In the conversion to AlN, it inhibits initial recrystallization and promotes the occurrence and growth of secondary recrystallization. This method is called an acquired inhibitor. The high-low temperature slab heating process has different initial recrystallized grain sizes when decarburization annealing, and the initial recrystallization of the high temperature process is significantly smaller than the primary recrystallized grains heated by the low temperature slab, the former 10-12 μm, The latter is 20-23 μm. At present, the low temperature heating process of slab has become the mainstream process for producing high magnetic induction oriented steel in China. WISCO, Baosteel and Shougang are constantly optimizing this process.
  2.4 Application of AlN as Inhibitor Thin Slab Continuous Casting Process (CSP) on Electrical Steel
  In the 1970s, after the first energy crisis, the world steel industry faced a major issue of structural adjustment.
  The core of the adjustment is to simplify the long-term adoption of long-term processes to reduce investment, save energy, and produce thinner, wider products. After the mid-1980s, a number of international companies, including Germany's SMS and Demag, Italy's Danieli, Austria's VAI, and Japan's Sumitomo Metal, competed for a lot of research and development and made breakthroughs. On July 21, 1989, Nucor Steel Company of the United States adopted the CSP process developed by SMS Company and successfully built the production line at Crawfordsville Plant in Indiana, USA, marking the first industrialization of thin slab continuous casting and rolling technology in the world.
  In March 1999, the CSP production line put into production by ThyssenKrupp AG of Germany was called the second generation of thin slab continuous casting and rolling production line, and produced non-oriented steel for the first time, with silicon content less than 2.4% and 50,000 tons. (steel water). In August 2001, a new CSP production line was built at the AST plant in Italy. This line highlights the development and progress of the CSP process in the production of special alloys (stainless steel, electrical steel, etc.) with high alloy composition. Its design capacity is 1 million tons, and its product structure is: austenitic stainless steel, ferritic stainless steel, non-oriented electrical steel (Si% <3.5%), in addition, a small amount of C75 and C100 high carbon steel.
  In October 2002, a total of 115,000 tons (including 88,000 tons of stainless steel, 17,000 tons of electrical steel and 10,000 tons of ferritic stainless steel), and Si=1.0%, 1.8% (no orientation) and 3.0% in electrical steel. (Orientation steel). Italian experts have believed that CSP can produce all grades including high magnetic induction oriented steel.
  The thin slab continuous casting and rolling process has obvious advantages compared with the traditional thick slab process. The process is obviously shortened, the required equipment is greatly simplified, the production area is reduced correspondingly, the investment in unit product construction is significantly reduced, the energy consumption is reduced, the labor quota is reduced, the finished product rate is high, the operation time is short, and the production cost is more than the traditional thick slab continuous casting. Reduced by 18%.
  China's production of electrical steel with CSP was carried out under the promotion of the National Science and Technology Support Program “New Generation Recyclable Steel Process Technology”。 At that time, Academician Gan Yong of the Chinese Academy of Engineering paid special attention to and promoted the project and passed the continuous casting of Beijing Iron and Steel Research Institute. The center and the factory combined to select the conditional factory to carry out the experimental research work. Finally, in March 2005, the first volume of China's first volume equivalent to 50W540 electrical steel hot rolled coil was produced in Maanshan Iron and Steel Co., Ltd.
  At present, China's production of medium and low grade non-oriented steel with CSP has become normalized (Wugang, Maanshan Iron and Steel), high grade is still under development, and oriented steel has completed the country under the joint efforts of Beijing Steel Research Institute Continuous Casting Center and Wuhan Iron and Steel Co., Ltd. The steel type development plan issued by the Ministry of Science and Technology. Wu Gang has made major breakthroughs in the development of high magnetic induction oriented steel, and basically established and improved the process standard. Currently, 0.27mm thick P1.7/50≤1.0W/kg, B8≥1.90T, can be mass-produced, optimized, further There is potential to improve magnetic properties, but due to the inherent problems brought about by the CSP process itself, the surface quality of the product still needs further improvement.
  ESP and CSP process flow properties are basically the same, the difference is no-head rolling, and has many advantages than CSP, but the application on electrical steel is rare. In the future, the ESP process for the development of different types of electrical steel is a very A meaningful topic.
  3Research and development of the process of producing electrical steel by thin strip continuous casting and rolling process
  In the 1980s, many manufacturers, such as the United States, Japan, and Germany, announced the success of using twin-roll or single-roll cast stainless steel and electrical steel. In 1984, Japan's Kawasaki Steel was cast by a two-roller method to produce high-silicon steel and carbon steel of 0.2-0.6 mm thick and 500 mm wide.
  As early as 1958, Northeastern University of China carried out the use of a different diameter double-roller casting mill, taking the process route of light casting and rapid casting and rolling, and casting and rolling out electrical steel plates and cast iron plates in the laboratory, and casting and rolling out in 1960. The steel plate and iron plate with a width of 600mm and a thickness of 2-2.5mm each have more than 100 tons, which was the international leading level at that time. Later, due to various domestic factors, the research work was interrupted. Until the 1980s, Northeastern University resumed research work.