Stainless Steel Grades

There are over 100 different grades of the material "rustproof stainless steel", which are currently available for a wide variety of applications. With such a large variety, and since stainless steel is not just stainless steel, it makes great sense to take a closer look at the differences between individual alloys (stainless steel grades) and their classifications in categories.

What is the material grade?

The material grade is the precise designation that identifies each individual alloy of stainless steel and can be assigned to the respective requirements or properties of the individual material.

Depending on the country, the designations of stainless steel grades, which are composed of alphabetic and numeric characters, are determined by the rules and regulations of each country.

For example, the United States has a different designation system for stainless steel grades than European or other non-European countries. Material grades refer to AISI (American Iron and Steel Institute) specifications. However, In Europe, they are defined by DIN (Deutsche Industrie Norm), AFNOR (Association française de normalisation), BS (British Standards) or European Standard (EN).

The structure of the material grade designation

The designation of stainless steel is subject to various international standards. In the 1930s and 1940s, both the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE) were involved in the work on standardization of a numbering system for steels. These efforts were of a very similar nature and in some cases strongly overlapped. For several decades, the systems were combined into a common system called "AISI/SAE steel grades system". In 1995, the AISI handed over further maintenance to the SAE system as the AISI itself had not developed any specifications. This designation system is commonly used for identifying different types of steel. But how exactly does it work? With a three-letter acronym with an optional additional letter.

The resistance class of steel is determined by the first figure, as in the following selection of examples:

• AISI-2XX - Austenitic Chromium-Nickel-Manganese Alloys
• AISI-3XX - Austenitic Chromium-Nickel Alloys
• AISI-4XX - Ferritic and Martensitic Chromium Alloys
• AISI-5XX - Heat Resisting Chromium Alloys

The second pair of figures is the ordinal number of the material in each class and serves to distinguish one quality from the other.

The optional following letters provide further information about the chemical composition and the resulting properties. For example:

• L = low carbon               = good weldability
• Ti = includes titanium = very high resistance to corrosion
• F = includes sulfur         = easier to machine
• N = includes nitrogen = high chemical resistance

Finally, a brief overview of the chemical compositions of the most common grades:

• AISI 430 - Cr (16–18 %) C (0.08 %)
• AISI 304 - Cr (18 %) Ni (10 %) C (0.05 %)
• AISI 304L - (Low Carbon): Cr (18 %) Ni (10 %) C (< 0.03 %)
• AISI 316 - Cr (16 %) Ni (11.3–13 %) Mo (2/3 %)
• AISI 316L - (Low Carbon): Cr (16.5–18.5 %) Ni (10,5–13,5 %) Mo (2–2.25 %) C (< 0.03 %)

How stainless steel grades are categorized internationally

The European Standard for the designation of steel grades is widely known all over the world. We would like to explain this using the most common stainless steel grade 1.4301.

The first figure, in this case the "1", stands for the main material group and indicates which material you are dealing with. All types of steel and steel alloys are combined in main group 1.

The next two figures, "43", stand for the grade class and provide information, whether these are structural steels, tool steels, roller-bearing steels or container steels. Indications about the carbon content or about properties such as heat and corrosion resistance or chemical resistance and magnetism properties can be found in the figures for the grade class, too.

The other two figures, "01", are the numerical number to differentiate between the stainless steel grades that belong to the same steel group or, in the case of non-ferrous materials, have the same grade number. However, they do not give any information about the composition of the stainless steel material.

Chemical formulas of stainless steel

There are also designation for stainless steel grades like "X5 CrNi 18-10" – what are these all about?

In addition to the slightly less complex material designations for the chrome-nickel steel AISI 304 (1.4301), the material AISI 316L (1.4404) or the stainless steel AISI 316Ti (1.4571), there are also a large number of sometimes very complex designations, such as X12CrMnNiN17-7-5, X1NiCrMoCuN25-20-5, X1NiCrMoCuN25-20-7, X2CrNiMnMoNbN25-18-5-4, X2CrNiMo18-15-4, X2CrNiMoN17-11-2, X2CrNiMoN17-13-3, X2CrNiMoN17-13-5, GX5CrNiMoNb19-11-2, X3CrNiCu18-9-4, X3CrNiMo17-13-3, X3CrNiMo18-12-3, X3CrNiMoN27-5-2, X2CrNi19-11,X2CrNiMo17-12-2, X2CrNiMo18-14-3, X2CrNiMoN22-5-3, X5CrNiMo17-12-2, X6CrNiMoTi17-12-2, X8CrNiS18-9, X10CrNi18-8, X2CrNi18-9, or for example X5CrNi18-10 for our above mentioned material AISI 304.

These more detailed stainless steel grade designations provide information about the chemical compositions of the grades and thus also about their physical properties.

Stainless steel & Material grades

Please see below a table for a better overview:

What do A2 and A4 stand for?

A2 (V2A) and A4 (V4A) are the short designations in German speaking countries for those stainless steels that are used in large quantities every day.

The letter V stands for the German word “Versuch” (that means “experiment”, “test”), the figure for the numerical number of the test and the A for “austenite”.

For the exact designation of stainless steel, however, experts use a material identification according to standard DIN ISO EN, for example grade 1.4301 for V2A and grade 1.4401, 1.4404 or 1.4571 for V4A.

There is a very strong demand worldwide for these stainless steel grades, as they can be used in architecture and a wide range of industries and meet ideally multiple requirements in terms of appearance and durability.

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