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Cause of edge crack of cold rolled electrical steel and improvement measures

05 Feb 2024
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GNEE Steel Cold Rolled Grain Oriented Steel
Because of the high brittleness of electrical steel, its edge cracking is particularly serious in the production process, which directly leads to the decline of the edge quality of the strip, and even leads to the fracture of the strip in serious cases, which greatly reduces the output of electrical steel products. Based on the situation of each grade of non-oriented electrical steel produced on site, the corresponding improvement measures are put forward.

With the continuous acceleration and development of China's modern industry and the further improvement of the level of social development, people have higher and higher requirements for iron and steel products in their daily lives. For the increasing attention of environmental protection countries, clean energy and materials are more important. Such as China's new energy vehicles, wind power generation, all kinds of motor development by leaps and bounds, such industries need to use the core material - electrical steel, also known as electrical steel. The silicon element in silicon steel can improve the resistivity of the matrix, reduce eddy current and hysteresis loss, increase the permeability and weaken the phenomenon of magnetic aging. Therefore, electrical steel can be used as an important magnetic material for various motors, generators, relays and transformers. However, the excessive silicon content in electrical steel will lead to the formation of brittle phases on the lattice, thereby increasing the brittleness of the steel, and it is difficult to carry out large deformation processing of the material. In recent decades, cold-rolled electrical steel gradually replaced hot-rolled electrical steel, but the cold-rolled silicon steel production process complex product impurity tolerance rate is very low, complex manufacturing process, product quality is extremely difficult to control, therefore, cold-rolled electrical steel industry has become the steel products in the "crown and art".

In the production of cold-rolled electrical steel, edge cracking has always been a "heart disease" that troubles the development of electrical steel industry. Through the energy spectrum analysis of inclusions and edge cracks in cold rolled electrical steel, it is found that the composition elements are similar to the mold powder, and it is speculated that the mold powder is brought to the bad surface of the plate during the continuous casting process before hot rolling. In the subsequent hot rolling process, surface defects are created and further expanded in the cold rolling process. The process parameters of cold rolling also have great influence on the notch deformation process of strip edge, such as tension, reduction rate, rolling speed, friction coefficient and so on.
Cold rolled oriented electrical steel
CRGO Silicon Steel
In modern scale production, we in order to meet the huge production demand, the required rolling speed is also higher and higher, under normal circumstances, the higher the rolling speed, the smaller the rolling force required, the smaller the power consumption of the motor, through the field test, the roughness of the rolled surface is compared. With the increase of speed, the friction coefficient between rolling and strip steel changes little, so we can conclude that the effect of rolling speed on the edge crack is almost negligible.

Timely communication with the previous process, as far as possible to reduce the slag contained in the hot rolled plate, improve the quality of raw materials. Since the cooling rate of the strip edge is faster than that of the central cooling, hot rolling can increase the thermal insulation device when necessary to ensure the uniform cooling temperature of the strip edge and the middle, reduce the temperature difference between the edge and the middle, and reduce the increase of the edge crack caused by the uneven cooling of the hot rolling raw material. Optimize the cold rolling process parameters for each grade, especially adjust the reduction rate of each pass (single-stand mill) of each grade, reasonable distribution, according to the equipment of the roll on site, "root diameter size", the state of process lubrication, etc., under the premise of ensuring that no cracks are produced, increase the reduction rate of the front pass, refine the grain, to prevent the crack increase again in the back pass.
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