Silicon steel, also known as electrical steel or silicon electrical steel, is a special type of steel that contains silicon in varying amounts. The grade or specification of silicon steel is typically denoted by a combination of numbers and letters that indicate its magnetic and electrical properties. The specific grades can vary depending on the standards followed by different countries or organizations.

One widely used classification system for silicon steel grades is the International Electrotechnical Commission (IEC) standard, which categorizes them into different classes based on their core losses. The IEC 60404-8-4 standard defines the classification of electrical steel grades, and the grades are designated by a combination of letters and numbers.

For example, one common grade of silicon steel is known as M-15. The "M" indicates that it is a non-oriented electrical steel, and the "15" refers to the specific core loss value in watts per kilogram at a certain frequency and magnetic induction level.

Another widely recognized classification system is the American Iron and Steel Institute (AISI) standard, which assigns grades to silicon steel based on their magnetic properties. These grades are typically represented by a four-digit number.

It's important to note that the specific grades and their corresponding properties may differ based on the applicable standards and regional variations. Therefore, it is advisable to consult the relevant standards or specifications for precise information regarding the grade of silicon steel.