Full-Processed versus semi-processed
There are two main types of silicon electrical steel: fully-processed (FP) and semi-processed (SP). Full-Processed EI silicon steels are mill-finished and have complete magnetic development. Semi-processed EI silicon steels require a final heat treatment, known as a Quality Development Anneal or a Stress Relief Anneal, to achieve optimum magnetic properties.
The difference between full-processed and semi-processed EI silicon steel sheets can be seen through measurements of the leakage flux. The leakage flux of a fully-processed EI silicon steel sheet is significantly higher than that of a semi-processed EI silicon steel. This finding demonstrates a strong correlation between leakage flux and material properties.
Full-Processed EI silicon steel sheet has a higher magnetic conductivity than semi-processed EI silicon steel. This characteristic is the result of the special processes applied to the steel. The grain orientation of the EI steel sheet is designed to correspond with the direction of magnetic flux flow in large scale transformers.
Magnetic properties of silicon steels
Single-phase EI silicon steel is one of the most important soft magnetic materials in use today. Its applications range from a few ounces in relays to tons in generators and motors. Silicon steels are particularly useful in electrical power generation because they minimize wasteful energy dissipation and reduce physical dimensions of equipment. While iron was the first soft magnetic material used, researchers soon found that adding silicon to the mix increased the material's resistivity, decreased hysteresis loss and reduced magnetostriction. This material is also less susceptible to aging.
The magnetic properties of single-phase EI silicon steel sheets depend on several factors, including their grain orientation, size, strain, and surface smoothness. The presence of impurities in single-phase EI silicon steel sheet is not detrimental to the magnetic properties but has an impact on the process. Impurities in the material interfere with the domain wall movement. While silicon steel is exceptionally pure, impurities such as carbon may reduce induction permeability and must be removed before the final texture can be produced.
Besides dimensional stability, EI steel is characterized by its high-permeability, low coercivity, and high saturation magnetization. These characteristics make it ideal for magnetic fields and are important for electrical machines. The material's hysteresis area is small compared to round wire, which results in a fill factor of about one.
Characteristics of silicon steels
Single-phase EI silicon steel sheet is characterized by a carbon content of 0.01% to 1%, Si content of 0.2% to 6.5%, and no more than 5% Mn content. Moreover, it is characterized by a substantially single a-ferrite phase, and a crystalline structure with columnar crystals that grow in a perpendicular direction.
The resulting material exhibits a high degree of resistivity. It is also resistant to eddy currents. This property makes the material an excellent candidate for magnetic core materials in electric motors, generators, and transformers. Furthermore, it is characterized by its low magnetic energy loss in AC magnetic fields, as well as its high flux density.
A high content of silicon allows for a high permeability and low hysteresis loss, which make the material suitable for transformer cores. It also has a low noise and low loss, making it ideal for miniaturizing and high-speed electrical equipment. However, cold-rolled silicon steel sheet is more expensive than hot-rolled steel, which makes it a more expensive option. Nevertheless, it has several advantages over hot-rolled steel.
Applications of silicon steels
The main applications of single-phase EI silicon steels are in high-speed motors and transformers. They are made from 5% si electrical steel, which is a soft magnetic material that has low noise and loss. As a result, these steels are ideal for making miniaturized, high-speed equipment. However, their disadvantage is that they are very brittle. To combat this problem, some researchers are working to improve the processing performance of single-phase silicon steels.
Single-phase EI silicon steels are available in two forms - Fully-Processed (FP) and Semi-Processed (SP). FP silicon steels undergo complete magnetic development in the mill. In contrast, SP silicon steels require a final heat treatment, called Quality Development Anneal (QDA) or Stress Relief Anneal (SRA), in order to achieve optimal magnetic performance.
The single-phase EI silicon steels are suitable for transformers of two to five-watt capacity. The EI35 section is selected for this application. The silicon steel sheet is placed over the middle part of the laminated iron core. Moreover, the ratio between the oriented silicon steel sheet and the iron core is relatively large, enabling high-frequency components to be carried by the oriented silicon steel.