Steel is a material used for a variety of applications, and each individual grade of steel has distinct characteristics and properties. In order to ensure that the specific steel is used for a specific purpose, steel grades are denoted by a series of numbers and letters. There are a variety of standards and nomenclature systems for denoting the different properties of a particular grade of steel, and these are important for applicants and engineers to understand when selecting and working with steel. This article will explain the basics of steel grades, including their different systems and nomenclature, as well as how they are applied.
One of the most common numbering systems for steel grades is published by the Society of Automotive Engineers (SAE). This system uses a two- or three-digit number followed by a letter to denote the steels properties and characteristics. The first number indicates the type of steel, while the letter indicates certain special characteristics. For example, 1018 is a plain carbon steel with a 0.18% carbon content. The letter L indicates that the steel is low carbon, while the letter H indicates it is a high carbon steel.
Another common steel grade nomenclature system is recognised by the American Iron and Steel Institute (AISI). This system also uses a two- or three-digit number followed by a letter, although the first number indicates the type of steel and the second number indicates the steels specific properties. For example, a 1045 steel has a 0.45% carbon content, which is higher than the 0.18% carbon content of a 1018 steel. Each steel grade is further divided into four classes, denoted by the letter following the number.
The European Union (EU) also publishes its own steel grades, which use a four-digit number with a single letter. The first two digits of the number indicate the steels chemical composition, while the third and fourth digits indicate its mechanical properties. The letter following the number indicates the steels strength. For example, a S235JR steel is a structural grade steel with a hardness of 235, or tensile strength of 235, which is slightly less than the 265 of a S275JR steel.
The Unified Numbering System (UNS) is another international steel grade nomenclature system. This system is most commonly used in the aerospace, military, and automotive industries. The UNS system also uses four-digit numbers and a single letter, with the first two digits indicating the steels chemical composition, the third its mechanical properties, and the fourth its heat treatment. The letter at the end of the number indicates its strength. For example, a S30300 steel is a stainless steel with a tensile strength of 300, or 30,000 psi (pounds per square inch).
Finally, the British Standard Numbering System (BS) is used in Europe, the UK, and Australia. This system uses a two- or three-digit code followed by a letter to denote the steels characteristics. The first number indicates the steels mechanical properties, while the second its chemical composition, and the letter at the end its specific properties. For example, a BS42S20 steel has a yield strength of 420, a tensile strength of 520, and a 0.2% carbon content.
In conclusion, there are a variety of steel grade nomenclature systems used around the world, each with distinctive designations granted to each steel grade. Understanding the different systems and the codes associated with each grade is important for applicants and engineers when selecting the best steel for their needs.
