AISI and SAE How are the numbers made up?

All carbon steels or alloy steels are given a number consisting of prefixes and suffixes. The number can have either three or four digits. The AISI steel and AISI stainless steel main classes 200, 300, 400, 500 and 600 are of particular importance. These are either austenitic, ferritic or martensitic alloys, which differ in terms of both their structure and their properties. The 1st digit characterises the respective main element of the alloy. The 2nd digit represents the grade class of the steel and the last digit or the last two digits characterise the carbon content.

AISI for stainless steels Main classes and series

There are various main classes between AISI 200 and 600, which are explained below. Class 200 is reserved for austenitic chromium-nickel alloys. The same applies to class 300.
Ferritic and martensitic chromium alloys are summarised in the main class 400. AISI 500 refers to heat-resistant chromium alloys, while class AISI 600 includes martensitic precipitation hardening alloys.

Materials What does austenitic mean?

Chromium-nickel alloys are described as austenitic if they are not only resistant to rust, but also completely rust-free. They are easy to process, malleable, tough and corrosion-resistant. The nickel content is at least 8 per cent.

Materials What does ferritic and martensitic mean?

Ferritic alloys have a crystalline structure, are easily deformable and highly magnetic. This is a significant difference to austenitic alloys. In martensitic alloys, the chromium content must be 10.5 to 13 per cent and the carbon content 0.2 to 1 per cent. If these values are exceeded or fallen short of, the alloys in question can no longer be labelled as martensitic.

Materials What does heat resistance mean?

The main class AISI 500 includes chrome alloys that are particularly heat-resistant due to their special properties. This means that they are able to withstand very high temperatures of 800 to 1400 degrees Celsius or even more without damage. The upper limit depends on various factors relating to the composition of the respective materials.

Assignment of steel keys AISI classification and material number according to DIN

Steel and stainless steel can be classified not only by the American Iron and Steel Institute (AISI), but also according to DIN (German Industrial Standard). Here, the 1st digit represents the main material group. The 2nd and 3rd digits are reserved for the grade number and the steel group respectively. The 4th and 5th or the 6th and 7th digits are exclusively counting numbers. The 6th and 7th digits can also be omitted.

The AISI number and the material number according to DIN can be assigned as follows: