# Designations of stainless steels

Extract from standard DIN EN ISO 3506.

Steel groups and strength classes are designated by a sequence of letters and numbers consisting of 4 characters:

In this article

1. The letters denote the general classification of the steel groups 2. The first digit after the letter denotes the metal alloying elements 3. The last two digits denote the strength class 4. ISO – Steel groups – Designations of stainless and acid-resistant steels

## 1 The letters denote the general classification of the steel groups:

- A = austenitic steels
- C = martensitic steels
- F = ferritic steels

## 2 The first digit after the letter denotes the metal alloying elements as follows:

- 1 – Chromium-nickel alloying elements, but a high sulphur and phosphorus content; because of this, however, it is easy to machine, difficult to weld, and its corrosion resistance decreases during machining.
- 2 – Chromium-nickel alloying elements. A widely used type of stainless steel.
- 3 – Chromium-nickel-titanium alloying elements. Stabilised stainless steel. For use at high temperatures.
- 4 – Chromium-nickel-molybdenum alloying elements. Acid-resistant steel.
- 5 – Chromium-nickel-molybdenum-titanium alloying elements. Stabilised acid-resistant steel. For use at high temperatures.

## 3 The last two digits denote the strength class

Let’s look at two examples!

- 1 `A2-70` = austenitic steel, with chromium-nickel alloying elements, cold worked, tensile strength at least 700 N/mm2
- 2 `C4-70` = martensitic chromium steel, hardened, tensile strength at least 700 N/mm2.

## 4 ISO – Steel groups – Designations of stainless and acid-resistant steels

![ISO – Steel groups – Designations of stainless and acid-resistant steels](https://menet-trend.hu/wp-content/uploads/menet-trend/iso-acelcsoportok.jpg)

* The designation of stainless steels with a low carbon content (below 0.03%) may be supplemented with the letter L. For example: A4L-80

A continuation of this article follows, in which we give the material composition of the alloys.

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