Introduction
Enhancing Quality and Efficiency Grain-Oriented Silicon Steel Production
The primary goal of cold-rolled grain-oriented silicon steel production is ensuring product quality and meeting quality and technical requirements. Increasing production capacity is another objective, relying on both the rationality of the production process and the full utilization of time and equipment, along with the technical skills of operators. Additionally, efforts should focus on reducing costs while enhancing production capacity and quality.
Production Processes of Cold-Rolled Grain-Oriented Silicon Steel
Overview of Production Methods
The production organization of grain-oriented silicon steel involves organizing and preparing raw materials, utilizing and maintaining equipment, and establishing technical procedures. Production processes and operating methods vary for different cold-rolled grain-oriented silicon steels based on their applications. Here’s a brief overview of the current production processes for cold-rolled grain-oriented silicon steel both domestically and internationally.
Double Cold Rolling Method
The production of cold-rolled grain-oriented silicon steel involves two methods: the single cold rolling method and the double cold rolling method. The double cold rolling method is generally utilized for producing general grades of grain-oriented silicon steel. It includes cold rolling the hot-rolled strip to an intermediate thickness, followed by annealing. Then, it undergoes a secondary cold rolling process to achieve the final thickness, followed by final annealing and other processes. One of its basic characteristics is using MnS or MnSe as beneficial inclusions to suppress the growth of primary grains. Another characteristic is employing moderate reduction rates during cold rolling to form a deformation texture.
Single Cold Rolling Method
The single cold rolling method produces high magnetic induction grain-oriented silicon steel. It involves subjecting the hot-rolled strip to normalizing treatment, followed by single cold rolling to the final thickness, and then decarburization annealing. Its production characteristics include: (1) using AlN+MnS (primarily AlN) as beneficial inclusions to suppress the growth of primary grains and promote grain growth; and (2) forming recrystallization texture through cold rolling with a large reduction rate of 85%.
Challenges and Key Points in the Production Process of Grain-Oriented Silicon Steel
Narrow Composition Control Range in Smelting
Smelting faces a challenge due to the narrow range of composition control. This range is much narrower than that of ordinary low-carbon steel and cold-rolled sheet steel. For thinner sheets, the composition range becomes even narrower, posing difficulties with conventional smelting equipment and analytical methods. Fluctuations in composition directly impact process performance and the final product. Composition control relies on vacuum refining equipment, involving alloy weighing and rapid, accurate component analysis. Reducing composition fluctuations requires optimization throughout the steelmaking and continuous casting process, particularly in refining and continuous casting.
Control of Purity in Smelting
The control of purity includes not only reducing oxide inclusions but also reducing the elements NB, V, Ti that form stable carbides and the elements Mg, Ca that form sulfides, which directly affect the behavior of inhibitors’ precipitation. These elements are mainly introduced into the molten steel with scrap steel, iron alloys, and refractory materials, so it is necessary to strengthen the procurement and management of these raw materials.
Composition Segregation and Cracking of Cast Ingots in Smelting
Due to the high sulfur content and low manganese content in grain-oriented silicon steel, cast ingots are prone to internal cracks and segregation. The solution is to adopt measures such as low superheat casting, electromagnetic stirring, and light pressure casting for ingots, adjust the casting machine regularly to reduce the central segregation and internal cracks caused by high sulfur content, and reduce the columnar crystal ratio.
Challenges in Hot Rolling Process: High-temperature Heating of Cast Ingots
To ensure complete dissolution of inhibitors like MnS and AlN, especially MnS, cast ingots require high-temperature heating and prolonged warming, leading to potential oxidation and burning loss. Before entering the furnace, the ingot surface above 300°C is sprayed with an anti-oxidant to prevent oxidation. Some steel companies spray the ingot surface above 500°C with a solution of MoO3 or CaMoO4 to prevent grain boundary cracks and improve surface quality. Additionally, some manufacturers apply anti-oxidation coating to ingots before furnace entry.
Key Points in Cold Rolling Process: High-Temperature Annealing
For general grain-oriented silicon steel, to obtain good grain orientation, a slow heating rate should be adopted to ensure that the grains with good orientation grow preferentially and undergo secondary recrystallization. For Hi-B steel, it is necessary to control the temperature and atmosphere at each stage of the high-temperature annealing process to ensure magnetic properties and the formation of a good base.