What Is Electrical Steel?

Silicon steel sheet, the English name is silicon lamination, it is a silicon-iron soft magnetic alloy containing extremely low carbon, and generally contains 0.5 to 4.5% silicon. Adding silicon can increase the resistivity and maximum magnetic permeability of iron, reduce coercive force, core loss (iron loss), and magnetic aging.

Silicon steel sheet

The production of silicon steel sheet is known as a handicraft in iron and steel products, especially oriented silicon steel sheet, due to the complicated process, narrow process window and difficult production. See picture

Mainly used to make various transformers, motors and generators

In 1900, Britain Hadfield (RAHadfield) first discovered that Si-Fe alloy containing Si4% has good magnetic properties. In 1903, Germany and the United States successively produced hot-rolled silicon steel sheets containing Si1.0 to 4.5%. Replaced in 1906

The requirements for the performance of silicon steel are mainly: low iron loss, which is the most important indicator of the quality of silicon steel sheet. Each country divides the grade according to the iron loss value. The lower the iron loss, the higher the grade. High magnetic induction strength (magnetic induction) under strong magnetic field, which reduces the volume and weight of the iron core of the motor and transformer, saving silicon steel sheets, copper wires and insulation materials. The surface is smooth, flat and uniform in thickness, which can improve the filling factor of the iron core. Good punching performance is more important for manufacturing miniature and small motors. The surface insulation film has good adhesion and solderability, which can prevent corrosion and improve punchability. Basically no magnetic aging. See Table 1 for typical electromagnetic performance.

Silicon steel is mainly smelted in an oxygen converter (also arc furnace smelting), combined with molten steel vacuum treatment and AOD technology (see Out-of-furnace refining, using die casting or continuous casting. According to different purposes, silicon is changed during smelting (0.5-4.5%) And aluminum (0.2 0.5%) content to meet the requirements of different magnetic properties. The silicon and aluminum content of high-grade silicon steel sheet will increase accordingly. Carbon, sulfur and inclusions should be reduced as much as possible.

Cold rolled silicon steel sheet has better magnetic properties, surface quality, filling factor and punchability than hot rolled silicon steel sheet, and can be produced in coils, so some countries have stopped producing hot rolled silicon steel sheet since the 1960s. In China, hot-rolled silicon steel sheets are manufactured by a rapid hot rolling at a low temperature of about 900 ° C and a stack annealing method under the protection of hydrogen, which has a high yield and a good surface quality and magnetic properties of the finished product.

The rolling of silicon steel is divided into two processes: hot rolling and cold rolling. The traditional process of directly producing silicon steel products by hot rolling has been rarely used. It is mainly produced by two processes: hot rolling and cold rolling. It is called cold rolling silicon steel. product. According to different products, the cold rolling process is divided into multi-stand rolling and single stand rolling, of which single stand rolling mainly produces oriented silicon steel products.

Cold-rolled non-oriented silicon steel sheet is a hot rolled steel slab or continuous casting slab into a strip with a thickness of about 2.3 mm. When manufacturing low-silicon products, hot-rolled strip coils are once cold-rolled to a thickness of 0.5 mm after pickling. When manufacturing high silicon products, hot-rolled strips are pickled (or normalized at 800-850 ° C and then pickled), cold-rolled to a thickness of 0.55 or 0.37mm, and annealed in a continuous furnace at 850 ° C in a hydrogen-nitrogen mixed atmosphere. Cold rolled to a thickness of 0.50 or 0.35mm after a small reduction of 6 to 10%. This small reduction of cold rolling can make the grains grow during annealing and reduce iron loss. These two cold-rolled sheets are finally annealed in a continuous furnace at 850 ° C in a 20% hydrogen-nitrogen mixed atmosphere, and then coated with a phosphate plus chromate insulating film. Grain-oriented silicon steel generally contains Si3%, which requires low oxide inclusions in the steel, and must contain C0.03 ~ 0.05% and inhibitors (second phase dispersed particles or grain boundary segregation elements). The role of the inhibitor is to prevent the growth of primary recrystallized grains and promote the development of secondary recrystallization, thereby obtaining a high (110) [001] orientation. The inhibitor itself is harmful to the magnetism, so after the inhibitory effect is completed, it must be annealed at high temperature. When the second phase inhibitor is used, the slab heating temperature must be increased to solid solution the original coarse second phase particles, and then precipitated as fine particles during hot rolling or normalization in order to enhance the suppression effect. The thickness of the cold rolled product is 0.28, 0.30 or 0.35mm. Cold-rolled oriented thin silicon steel strip is made of 0.30 or 0.35 mm thick oriented silicon steel strip, and then pickled, cold rolled and annealed.

Silicon steel sheet annealing

Stress relief annealing process of silicon steel sheet

^[1]

First, put the silicon steel sheet to be annealed into the iron box (according to the size of the silicon steel sheet, pay attention to the box is preferably not more than three layers) loading rack, each box of silicon steel sheet is preferably covered with a cover slightly smaller than the iron box It is best to use silicon steel sheet material), hang it in the furnace, lock the furnace cover, press the seal ring, and connect the circulating water pipe.

2. Connect nitrogen, check for leaks, and check the normal supply of circulating water.

3. Close all valves, install the vacuum tube, open the vacuum pump, open the vacuum valve, vacuum down to -1MPA, close the needle valve and turn off the vacuum pump power.

4. Connect the nitrogen tube to the inflation valve, open the inflation valve, and inject nitrogen. The pressure is between 0.03 and 0.1MPA. Close the inflation valve and open the safety valve.

5. Install the three thermocouples of the meter on the furnace body.

6. Check whether the voltage, current and meters of the electrical cabinet are normal.

7. Set the initial temperature of the temperature control meter to 400 ° C, check whether the currents of the power meter are consistent, and after ensuring that the adjustments are consistent, turn on the heating switch to heat. At this time, the valve of the circulating water is opened to ensure that there is no blockage and the water flows smoothly.

8. Check the normality of the electrical room instruments and adjust the power of the annealing furnace.

Nine, when the temperature rises to 400 , open the nitrogen filling valve (smoke exhaust), and close the inflation valve when the air is deflated to 0.01MPA (repeat the three and four operations)

10. When the temperature is determined to rise to 400 ° C, perform a constant temperature. The constant temperature is about 1 hour [approximately the time to operate the ninth item], and it is determined that the instrument temperature is also about 400 ° C.

11. After the insulation is completed, set the temperature control meter to 680 ° C and heat it.

Twelve, during heating, pay attention to the flow and temperature of the circulating water, the pointer of the pressure vacuum gauge should not exceed 0.1MPA; if it exceeds 0.1MPA, open the inflation valve to deflate, and always keep it at 0.1MPA

13. The temperature control meter is set to 680 750

(Depending on the material of silicon steel sheet, cold rolled non-oriented silicon steel sheet with low grade domestic BS0A600, 50W600, 50WW540 and lower general annealing temperature is around 680 , imported equivalent material can be appropriately + 20 , non-oriented high grade general annealing temperature is 720 about.

14. After the temperature rises to the set temperature, the constant temperature time should not be less than 2 hours, and the meter should also be above and below the set temperature.

15. After finishing, turn off the heating switch and power switch.

16. After the inspection is correct, the furnace's silicon steel sheet annealing process enters the natural cooling state. When the temperature in the furnace drops below 380 ° C (preferably 350 ° C), the vent valve is opened and the gas is released. Fill the furnace with compressed air for 5 minutes} Open the furnace cover before leaving the furnace. Lift the material rack, put it in a safe position and blow it tangentially with an electric fan until it cools to the desired temperature. At this time, the circulating water valve can be closed (the water outlet valve is always open).

Silicon steel sheet annealing furnace

Each country divides the grade according to the iron loss value. The lower the iron loss, the higher the grade. Common grades are B50A800.B50A470.B50A1300 and so on.