The primary goal of cold-rolled oriented electrical steel production is to ensure product quality and obtain products that meet quality requirements and technical requirements. Another task of electrical steel production is to strive to increase output. The completion of this task not only depends on the rationality of the production process, but also depends on the full utilization of time and equipment and the technical quality of the operator. In addition, efforts are made to reduce costs while improving output and quality.
The production organization of oriented electrical steel includes the organization and preparation of raw materials, the use and maintenance of equipment, and the formulation of technical regulations. Various cold-rolled oriented electrical steels have different production processes and operating methods according to their different uses. The following is a brief introduction to the current production technology of cold-rolled oriented electrical steel at home and abroad.
The production of cold-rolled oriented electrical steel includes primary cold rolling and secondary cold rolling. The secondary cold rolling method is generally used to produce general grades of grain-oriented electrical steel. It consists of hot-rolled strip cold rolling to an intermediate thickness and annealing, and then secondary cold rolling to the final thickness and final annealing. One of its basic features is to use MnS or MnSe as a favorable inclusion to suppress the growth of primary grains; its second basic feature is to use cold rolling at a medium reduction rate to form a deformation texture (111) [112]. The primary cold rolling method is a method used to produce high magnetic induction oriented electrical steel. It is to cold-roll the hot-rolled strip steel to the finished thickness after normalization treatment, and then perform decarburization annealing. Its production characteristics are: ① using AlN+MnS (mainly AlN) as favorable inclusions to inhibit the growth of primary grains and promote the growth of (110)[001] grains; ② formed at a high reduction rate of 85% Cold rolling deformation texture of recrystallized (110)[001].
Difficulties and key points in the production process of oriented electrical steel
1) One of the difficulties in smelting is the narrow range of ingredient control.
The allowable fluctuation range of the composition is much narrower than the composition range of ordinary low carbon steel and cold-rolled thin plate steel. Especially the thinner the plate, the narrower the composition range becomes, which is difficult to achieve using general smelting process equipment and analysis methods. Fluctuations in ingredients directly affect individual processes and the performance of the final product. The control of components is mainly carried out by using vacuum refining equipment, which involves the weighing of alloys and rapid and accurate analysis of components. Reducing component fluctuations involves the entire process of steelmaking and continuous casting, especially the refining and continuous casting processes.
2) The second difficulty in smelting is the control of purity.
Purity control not only includes reducing oxide inclusions, but also reducing elements NB, V, Ti that form stable carbides and elements that form sulfides, such as Mg and Ca. These elements directly affect the precipitation behavior of the inhibitor. These elements are mainly brought into molten steel along with scrap steel, ferroalloys and refractory materials. The procurement and management of these raw and auxiliary materials must be strengthened.
3) The third difficulty in smelting is the component segregation of the slab and the cracks in the slab.
Due to the high sulfur content and low manganese content of grain-oriented electrical steel, the cast slab is prone to internal cracking and segregation. The solution is to adopt measures such as low superheat casting, electromagnetic stirring and light pressing of the slab, and regularly adjust the condition of the casting machine to reduce central segregation and internal cracking caused by high sulfur, and reduce the columnar crystal ratio.
4) The difficulty of the hot rolling process is the high-temperature heating of the slab.
In order to completely dissolve inhibitors such as MnS and AlN, especially MnS, the cast slab needs to be heated at high temperature and kept warm for a period of time, which easily causes oxidation and burning loss of the cast slab. Nippon Steel Co., Ltd. sprays antioxidants on the surface of cast slabs with temperatures above 300°C before heating them in the furnace. In order to prevent grain boundary cracks formed by high-temperature heating and improve the surface quality of products, Kawasaki Steel Co., Ltd. sprays MoO3 or CaMoO4 aqueous solution on the surface of cast slabs with temperatures above 500°C. The practice of some manufacturers is to coat the cast slab with anti-oxidation coating before entering the furnace.
5) The focus of the cold rolling process is high temperature annealing.
For general grain-oriented electrical steel, in order to obtain good (110)[001] grain orientation, a slower heating speed should be used to ensure that the (110)[001] grains with good orientation grow preferentially and secondary regeneration occurs. crystallization. For Hi-B steel, the temperature and atmosphere at each stage of the high-temperature annealing process must be controlled to ensure magnetism and form a good bottom layer.
Low-temperature heating process in grain-oriented electrical steel
Reducing the heating temperature of grain-oriented electrical steel slabs has the advantages of avoiding the formation of liquid slag, reducing maintenance of the heating furnace, obtaining higher metal yield, and preventing undesirable grain coarsening in the middle of the slab. In recent years, when people are studying low-temperature heating of slabs, in order to ensure the strength of the inhibitor, other substances other than manganese sulfide, such as nitrides and grain boundary precipitated elements, have been added to strengthen the inhibitor.
The solid solution temperature of aluminum nitride is lower than that of manganese sulfide, so it is more suitable for low-temperature heating. At present, the industrial production method using the low-temperature heating process of slabs is to use aluminum nitride as an inhibitor and perform nitriding treatment before the start of secondary recrystallization, or to use aluminum nitride as the main inhibitor and Cu2S and manganese sulfide as the inhibitor. Auxiliary inhibitors. The method is to nitride the steel to combine with the original elements in the steel to form aluminum nitride precipitates with inhibitor functions. According to the aluminum nitride solution, the heating temperature of the slab can be lowered to 1150~1200°C. In order to obtain a complete secondary recrystallization structure, high magnetism and a good glass film, corresponding composition adjustments and process improvements must be made. The characteristics of the new Hi-B process studied by Nippon Steel are: using aluminum nitride as an inhibitor, the slab heating temperature is lowered to 1150~1250°C, and after decarburization and annealing, nitriding treatment is carried out in an H2+N2 atmosphere containing NH3. The one-time cold rolling method can produce products with a thickness of 0.18~0.50mm, and it is easier to make new products without glass film. Sumitomo Metal proposed a low-carbon 1.5% Mn-2.2% Si oriented electrical steel process using aluminum nitride as an inhibitor to reduce the slab heating temperature. South Korea's Pohang Steel Company proposed a process for producing general oriented electrical steel and high magnetic induction oriented electrical steel using aluminum nitride as the main inhibitor, Cu2S and manganese sulfide as auxiliary inhibitors, and heating the slab at 1250 to 1320°C.
