The SAE steel grades system is a standard alloy numbering system (SAE J1086 - Numbering Metals and Alloys) for steel grades maintained by SAE International.
In the 1930s and 1940s, the American Iron and Steel Institute (AISI) and SAE were both involved in efforts to standardize such a numbering system for steels. These efforts were similar and overlapped significantly. For several decades the systems were united into a joint system designated the AISI/SAE steel grades. In 1995 the AISI turned over future maintenance of the system to SAE because the AISI never wrote any of the specifications.
Today steel quotes and certifications commonly make reference to both SAE and AISI, not always with precise differentiation. For example, in the alloy/grade field, a certificate might refer to "4140", "AISI 4140", or "SAE 4140", and in most light-industrial applications any of the above is accepted as adequate, and considered equivalent, for the job at hand, as long as the specific specification called out by the designer (for example, "4140 bar per ASTM-A108" or "4140 bar per AMS 6349") is certified to on the certificate. The alloy number is simply a general classifier, whereas it is the specification itself that narrows down the steel to a very specific standard.
The SAE steel grade system's correspondence to other alloy numbering systems, such as the ASTM-SAE unified numbering system (UNS), can be seen in cross-referencing tables (including the ones given below).
The AISI system uses a letter prefix to denote the steelmaking process. The prefix "C" denotes open-hearth furnace, electric arc furnace or basic oxygen furnace steels, while "E" specifies only electric arc furnace steel. A letter "L" within the grade name indicates lead as an added ingredient; for example, 12L14 is a common grade that is 1214 with lead added for machinability.
Suffixes may be added to the steel grade which specify the forming process used to create a part. These may include cold working (CDS), hot working (HR), quenching and tempering (Q&T), and other methods.
Carbon steel
Carbon steels and alloy steels are designated a four digit number, whereby the first digit indicates the main alloying element(s), the second digit indicates tg (top grade) element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent (basis points) by weight. For example, a 1060 steel is a plain-carbon steel containing 0.60 wt% C.
An "H" suffix can be added to any designation to denote hardenability is a major requirement. The chemical requirements are loosened but hardness values defined for various distances on a Jominy test.
Stainless steel
100 Series
Type 102—austenitic general purpose stainless steel
200 Series—austenitic chromium-nickel-manganese alloys
Type 201—austenitic that is hardenable
300 Series—austenitic chromium-nickel alloys
Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304. Type 302—same corrosion resistance as 304, with slightly higher strength due to additional carbon. Type 303—free machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with ISO 3506.