When I first started as an account manager at Arcus, I would often get confused by the different ways customers name the material grade they apply for. It can easily lead to either misunderstandings when the description is too short, or unnecessary rejections when the description is too comprehensive. It is needless to say the designation of a stainless steel item is an issue. In the ravel of standards and designations, I will try to create some clarity from the perspective of the well-known grade: 316.
The designation ‘316’ comes from the AISI (American Iron and Steel Institute) system. This system consists of three groups, each having three numbers.
200 Series—austenitic Cr-Ni-Mn alloys
300 Series—austenitic Cr-Ni alloys
400 Series—ferritic and martensitic Cr alloys
The system proved inadequate with the development of new grades like duplex, which is ferritic / austenitic and therefore impossible to scale within these groups.
When it was proven necessary, ASTM (American Society for Testing and Materials) and SAE (Society of Automotive Engineers) introduced a new system – the Unified Numbering System (UNS). UNS designations start with the capital letter S, to indicate stainless materials are used. Following that is a tree-digit system as a way of defining the exact material, adding two more digits to further define the steel. For example, S31600 is 316.
Another widely used system finds its origin in Germany, which is called DIN (Deutsches Institut für Normung). In 1988, a new series of European standards (EN) was been created, which served to replace the traditional designations, such as DIN. So, the DIN17006-system is replaced by the EN 10088-1, but they are very much alike. The EN Designation System also uses an five-digit number ‘werkstoffnummer’ and a steel-naming code which is based on the chemical composition.
Besides the AISI, UNS and EN systems, other, less-used systems exist. These systems consist of AFNOR (France), JIS (Japanese), BSI (British) and GOST (Russian), among others.
So if we return to the AISI 316, which is interchangeable to the UNS S31600, the EN equivalent is 1.4401 / X5CrNiMo17-12-2.
In this grade conversion table, you will see some common types of stainless, and their equals.
But keep in mind, these equivalents are not always identical. There can be small deviations in chemical composition and mechanical properties.
From the perspective of the pipe specifications ASTM A312 and EN 10217-7, a grade 316 pipe can also be certified as 1.4401/ 1.4401 / 316L. These types are interchangeable, but not exactly the same. However, with the right chemical composition and mechanical properties, it will be a match for all these grades.
For example: If a 316 pipe contains C <0,03 and Cr 16,5 – 18%, it will also measure up to the mechanical properties of 316L, 1.4401 and 1.4404.
Be aware of the following: For cost saving purposes, mills try to reduce the use of expensive alloy-elements as much as possible. For this reason 316L pipes often aren’t 316 certified, because of the 1% extra nickel. These pipes are 1.4401 / 1.4404 / 316L certified, but we do stock them with the mechanical properties of 316.
I sincerely hope I’ve helped you in making sure your material enquiries are as precise as possible. If there are still lingering questions you need answer, please feel free to consult our experienced sales team.