Silicon steel is a ferrosilicon alloy with a silicon content of about 3% to 5% and the rest being mainly iron. It is an important soft magnetic alloy that is indispensable in the power, electronics and military industries. It is also the metal functional material with the largest production volume. It is mainly used as the iron core of various motors, generators and transformers. Its production process is complex and the manufacturing technology is strict. Foreign production technologies are protected in the form of patents and are regarded as the life of the enterprise.
The manufacturing technology and product quality of electrical steel plates are one of the important indicators to measure the level of special steel production and technological development of a country. At present, the quantity, quality, and specifications of cold-rolled electrical steel in my country cannot meet the needs of the development of the energy (power) industry. There is a large gap compared with Japan in terms of production technology, equipment, management, and scientific research.
Silicon is a good deoxidizer for steel. It combines with oxygen to convert oxygen into stable SiO2 that is not reduced by carbon, avoiding the lattice distortion of iron due to oxygen atom doping. Silicon becomes a solid solution in α-iron, which increases the resistivity and helps separate harmful impurities, carbon. Therefore, generally, adding silicon to iron containing impurities can increase the magnetic permeability, reduce coercive force and iron loss. However, increasing the silicon content will make the material hard and brittle, and the thermal conductivity and toughness will decrease, which is detrimental to heat dissipation and mechanical processing. Therefore, the silicon content of silicon steel sheets generally does not exceed 4.5%.
Silicon steel sheets are divided into two types: cold-rolled and hot-rolled. Cold-rolled silicon steel sheets are more commonly used. Cold-rolled silicon steel sheets have excellent magnetic properties along the rolling direction. They not only have high saturation magnetic flux density and low iron loss in strong magnetic fields, but also have good magnetic properties (large initial magnetic permeability) in weak magnetic fields. This is because the cold rolling process reduces the impurity content in the steel sheet and creates coarse grains in the steel sheet, which increases the magnetic permeability and reduces the hysteresis loss.
Silicon steel classification:
Hot rolled silicon steel sheet
Hot-rolled silicon steel sheets are made by melting Fe-Si alloy in an open furnace or electric furnace, repeatedly hot-rolling into thin sheets, and finally annealing at 800-850°C. Hot-rolled silicon steel sheets are mainly used in the manufacture of generators, so they are also called hot-rolled motor silicon steel sheets. However, their availability is low and energy loss is large. In recent years, relevant departments have ordered their elimination.
Cold rolled non-oriented silicon steel sheet
The main use of cold-rolled non-oriented silicon steel sheets is for generator manufacturing, so it is also called cold-rolled motor silicon steel. Its silicon content is 0.5%-3.0%, and it is cold rolled to the finished thickness. It is mostly supplied as 0.35mm and 0.5mm thick steel strips. The Bs of cold-rolled non-oriented silicon steel is higher than that of oriented silicon steel; compared with hot-rolled silicon steel, its thickness is uniform, dimensional accuracy is high, and the surface is smooth and flat, thereby improving the filling factor and the magnetic properties of the material.
Cold rolled oriented silicon steel sheet
The main use of cold-rolled oriented silicon steel strip is for transformer manufacturing, so it is also called cold-rolled transformer silicon steel. Compared with cold-rolled non-oriented silicon steel, the magnetism of oriented silicon steel has strong directionality; it has superior high magnetic permeability and low loss characteristics in the rolling direction that is easy to magnetize. The iron loss of the oriented steel strip in the rolling direction is only 1/3 of the transverse direction, and the magnetic permeability ratio is 6:1. Its iron loss is about 1/2 of the hot-rolled strip, and the magnetic permeability is 2.5 times that of the latter.
High magnetic induction cold rolled oriented silicon steel sheet
High magnetic induction cold-rolled silicon steel strips are all single-oriented steel strips and are mainly used in the manufacturing of various transformers, chokes and other electromagnetic components in the telecommunications and instrumentation industries. Its application has two main characteristics. One is that under small current conditions, that is, weak magnetic field conditions, the material is required to have high magnetic properties in the weak magnetic field range, that is, high μ0 value and high B value; the second characteristic is the frequency of use. High, usually above 400Hz, even as high as 2MHz. In order to reduce eddy current losses and effective magnetic permeability under alternating magnetic fields, thin strips of 0.05-0.20mm are generally used.
Silicon steel production process:
Pickling
Use the descaler and hydrochloric acid tank to remove oxides from the hot-rolled steel strip to prevent surface defects of the cold-rolled finished product.
Cold stamping
In order to ensure the thickness and material for different uses, the deceleration ratio is set at 40%-90%, and advanced control equipment such as automatic thickness control and automatic shape control are implemented.
Annealing
It is a process of softening the steel strip material that has been hardened in the cold stamping process. Through metal heating and rapid cooling, we produce steel for deep processing and high-tensile strength steel, and adopt boxing (hood annealing) annealing and continuous annealing methods.
Insulating coating
When processing a silicon steel plate into an iron core, in order to improve its processing performance and prevent eddy current losses equivalent to the multiplication of the thickness of the steel plate, continuous coating equipment is used to spray the insulating coating liquid on the upper and lower sides of the steel plate.
Performance:
The main performance requirements for silicon steel are:
1. Low iron loss, which is the most important indicator of the quality of silicon steel sheets. Countries all classify grades according to the iron loss value. The lower the iron loss, the higher the grade.
2. The magnetic induction intensity (magnetic induction) is high under a strong magnetic field, which reduces the size and weight of the cores of motors and transformers, saving silicon steel sheets, copper wires and insulating materials.
3. The surface is smooth, flat and uniform in thickness, which can improve the filling factor of the iron core.
4. Good punching properties are more important for manufacturing micro and small motors.
5. The surface insulation film has good adhesion and weldability, and can prevent corrosion and improve film punching.
