A grade is a way of classifying metals. A metal grade is designated by numbers, letters, or a combination of both. A metal grade is usually determined by its chemical composition, its mechanical properties, or both. There are many different organizations that create various standards for a given metal grade.
There are several reasons for the many different grades of metal.
- Metals can be manufactured in many different ways. The type of furnace that is used, the rate at which the metal is allowed to cool, and the forming process are all variables that can affect the resulting metal’s performance.
- The vast array of materials that are used to make a metallic compound. A metal such as aluminum can have a plethora of alloying elements added to it; all of which have an effect on the performance of the aluminum alloy.
- The varying mechanical properties of metals. Even with the same chemical composition, metals can vary in strength, ductility, and other mechanical attributes, so it is important to understand during the material selection process how a metal will respond to different types of loads and strains.
There are many organizations that have developed their own system to grade metals. The American Society for Testing and Materials has grades such as ASTM A36 and ASTM A240. The American Iron and Steel Institute gives out grades such as AISI 1018 and AISI 4140. Other organizations that have metal grading systems include the International Organization for Standardization, the European Standards, the British Standards, the Aerospace Material Standards and the Society of Automotive Engineers. There are also proprietary grades that are labeled by the manufacturer.