Technical points of new methods for oriented electrical steel
Oriented electrical steel, also known as grain-oriented silicon steel, is a type of cold-rolled electrical steel containing between 2.9% and 3.5% silicon. This material features a highly ordered crystal structure that enhances its magnetic properties. It plays a vital role in the power industry due to its excellent soft magnetic characteristics. During production, an MgO-based release agent is typically used to prevent adhesion during annealing. This involves applying a layer of stable inorganic material onto the surface of the steel sheet at high temperatures, which can sometimes lead to moisture on the surface and negatively impact the magnetic performance of the steel.
JFE Steel Corporation from Japan has introduced a groundbreaking method that eliminates the need for a release agent. The key technical aspects of this innovation are outlined below:
1. Technical Prerequisites: To enable continuous annealing without a coating, it's crucial to keep the sulfur (S) and selenium (Se) content as low as possible. This is a fundamental condition for achieving successful annealing without a separator.
2. Production Process: - Hot rolling is performed after heating the slab to a temperature below 1250°C. - The hot-rolled sheets are then annealed at a temperature range of 800–1100°C. - The sheets undergo two or more cold rolling processes, with an intermediate annealing step between each rolling stage. If decarburization is required, the first recrystallization annealing should be conducted under a humid atmosphere. Otherwise, a dry atmosphere can be used. - After the first recrystallization, a second recrystallization annealing is carried out at 700–1000°C, with an annealing time of at least 5 hours. - The final continuous annealing process is performed at a temperature above 1100°C, with a duration not exceeding 30 minutes—ideally around 10 minutes to achieve optimal magnetic properties. The annealing atmosphere can be argon (Ar), hydrogen (H₂), or helium (He).
According to testing results, JFE’s thick-oriented electrical steel with a thickness of 0.20 mm achieved an iron loss value (W17/50) of 0.584–0.648 W/kg, demonstrating outstanding electrical performance. This new method not only improves efficiency but also reduces the environmental impact associated with traditional release agents, making it a significant advancement in the field of electrical steel manufacturing.
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