Introduction:
Steel is one of the most important and widely used materials in the world, coming in countless shapes and forms and having countless applications. Steel is an alloy composed of iron and other elements, like chromium, nickel, and molybdenum, all of which can influence the properties of the steel. In the United States, different producers of steel adhere to a standard specifying steel grades and grade numbers, as defined by the American Iron and Steel Institute (AISI). This system assigns grade numbers to different ranges of compositions and mechanical properties, allowing manufacturers and consumers to more accurately identify, purchase, and track steel products.
History of the AISI:
The American Iron and Steel Institute was formed in 1855, making it one of the oldest organizations in the American metalworking industry. Originally named the American Iron Association, the AISI was formed to promote the iron and steel industry. Over time, the organization changed and grew, taking on new members and expanding its focus to other metals. In 1916, the AISI published the first comprehensive system of steel grades and number designations, which has since been updated and revised several times.
Grade Numbers and Designations:
The AISI uniform grade designations are used to group similar grades of steel together, and grade numbers are assigned numbers to the different grades. The AISI system for steel grade numbers contains three different series of designations. The first series, the A-series, contains carbon steels and carbon-manganese steels. The A-series designations are divided into two sections: low carbon (A1-A4) and high carbon (A5-A9). The second series of designations is the B-series. The B-series contains heat treatable alloy steels, but not stainless steels. The third series of designations is the C-series. The C-series contains stainless steels, and is divided into two sections: regular austenitic (C1-C7) and high alloy (C8-C12).
Alloying Elements and Grades:
The AISI system also includes a letter designation designating the main alloying elements in the steel. Each class of steel is assigned a letter, ranging from A (for carbon steels) to Z (for high alloy steels). The numbers that follow the letter designate the specific composition of the steel. For example, a steel designated as A5 would have a low carbon content, while a steel designated as D5 would have a high carbon content, and a steel designated as P5 would have a high molybdenum content.
Conclusion:
The American Iron and Steel Institute’s uniform grade designations system is an important tool for steel producers and users alike, allowing consumers to easily identify and purchase the exact steel products they need. By using the AISI system, steel producers and consumers can be sure that their steel has the right properties and composition.
