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Understanding the Steel Naming and Numbering System

by Feb 7, 2017News

The decision about materials for fabrication don’t stop at deciding on stainless steel. Stainless comes in a number of types, each with unique properties. Choosing the right steel number helps you ensure that the products you create have the composition and qualities that you need to make your operations a success.

Back in the 1930s and 1940s, the standards organization SAE International and the American Iron and Steel Institute (AISI) began working to standardize a numbering system for stainless steel. Their work overlapped a great deal. As a result, you will see older plans refer to AISI/SAE steel grades. In 1995, the AISI turned over the future maintenance of the numbering systems to the SAW. This is because the AISI was not the author of the specifications.

You will see steel quotes and certifications today that make reference to both AISI and SEA. Often, these are not precisely differentiated. For instance, you will see refernces to 317l stainless steel, AISI 317 or SAE 317. In most cases, these three can be treated as the same. However, if there are very specific needs, the standard chosen should be followed.

The AISI system also used a letter prefix that would say which steel making process was used. For instance, the letter E meant electric arc furnace steel; the letter C before the number meant that the steel was made in an open-heart furnace. When the letter L was used, that mean that lead had also been added.

In carbon and alloy steel, there is a four digit number. The first digit indicates the main alloying element. The second refers to the secondary allow. The last two digits say how much carbon is in the mix. For instance, if you see a reference to 1050 steel, it is carbon steel with .50 wt% carbon. An H suffix after any designation shows that hardenability is a major requirement. Hardness values are defined using a Jominy test.

Stainless steel has a three digit designation. The 200 series includes austenitic chromium-nickel-manganese allows. These are general purpose stainless steel.

The 300 series has a number of different purposes depending on additives. Type 302 offers high corrosion resistance, plus high strength. Type 304L differs from type 304 due to a lower carbon content to make it more weldable. Type 317 has higher levels of nickel and chromium; the L type has lower carbon.

Picking the right type starts with considering the application. Know what qualities you need during fabrication and operation. With this knowledge, you can choose the steel type that will ensure that you get the results that you want.