Steel Designations According to DIN EN 10027-1: A Simple Explanation of Naming Based on Chemical Composition

How to Correctly Interpret Steel Grades Based on Their Chemical Composition

10CrMo9-10, X120Mn12, C45, or 16Mo3 —anyone who works in the steel trade encounters these steel grades on a regular basis. Unlike steel designations such as S355J2+N or P355NH, however, the focus here is not on the intended application or the mechanical properties. Instead, the steel designation provides information about the carbon content and the most important alloying elements of the material.Naming based on chemical composition is also part of DIN EN 10027-1 and makes it possible to draw conclusions about the material’s composition and properties simply from the abbreviation.

What does naming based on chemical composition mean?

DIN EN 10027-1 specifies two different systems for designating steel grades. While the first part of this series of articles dealt with steel designations based on intended use and mechanical properties, this article focuses on designations based on chemical composition.

This classification system is not primarily concerned with properties such as yield strength or tensile strength, but rather with the internal structure of the material. This structure is largely determined by carbon content and alloying elements.

This makes it possible to determine important properties such as:

• Hardness
• Wear resistance
• Corrosion Resistance
• Heat resistance
• Toughness

can be deduced from the steel designation.

Why are there two naming systems within DIN EN 10027-1?

Depending on the material, different properties are of primary importance.

For structural steel, it is often sufficient to specify the intended use and the mechanical properties. For this reason, steel grades such as S355J2+N or P355NH are named according to their application and minimum yield strength.

Alloying elements such as chromium, nickel, molybdenum, or manganese play a key role in determining how a material behaves under stress, at different temperatures, or under wear. For this reason, the composition of these steels is directly reflected in their designations.

How are steel designations structured based on chemical composition?

The naming convention based on chemical composition also follows a clearly defined structure. Depending on the material, the steel designation provides information about the carbon content, the most important alloying elements, and their approximate proportions in the material.

In general, DIN EN 10027-1 distinguishes between three groups:

• Unalloyed Steels
• Low-alloy steels
• High-Alloy Steels

For each of these groups, there are specific rules for forming the steel designation.

Unalloyed Steels

Unalloyed steels begin with the letter C. The number that follows indicates the average carbon content in hundredths of a percent.

Example:

• C45 = approximately 0.45 percent carbon

Since the steel contains no significant alloying elements, the steel designation is usually limited to this information. The carbon content affects, among other things, the material’s strength, hardness, and machinability.

Low-alloy steels

Low-alloy steels contain, in addition to carbon, other alloying elements, the total content of which is generally less than 5%. These elements—such as chromium (Cr), molybdenum (Mo), or manganese (Mn)—are specifically added to improve properties such as strength, hardness, heat resistance, or toughness.

Typical applications include mechanical engineering, plant engineering, pressure vessel construction, and general steel construction.

The steel grade designation already provides important information about the material’s composition: It begins with the carbon content, followed by the chemical symbols of the alloying elements and what is known as an alloy index.

Examples of low-alloy steels:

High-Alloy Steels

High-alloy steels begin with the letter X. This designates materials in which at least one alloying element has an average content of 5 percent or more. This results in particularly high requirements for corrosion resistance, wear resistance, or temperature resistance.

The X is followed by the carbon content in hundredths of a percent. After that, the most important alloying elements and their approximate contents are listed directly as percentages.

These steels are used when standard or low-alloy steels reach their technical limits, particularly in the chemical industry, in plant engineering, or in applications subject to severe wear.

Example:

• X120Mn12 = high-alloy steel. Approx. 1.20% carbon, approx. 12% manganese content

The Most Important Alloying Elements and Their Significance

The properties of steel are largely determined by its alloying elements

The specific combination of these elements determines whether a steel is suitable for mechanical engineering, pressure vessels, wear-resistant applications, or corrosive environments.

Conclusion

Designation based on chemical composition is a central system within DIN EN 10027-1 and allows for the unambiguous description of steel materials based on their internal structure.

Steel designations such as 16Mo3, 10CrMo9-10, 42CrMo4, or X120Mn12 provide important information about carbon content and alloying elements even in their abbreviated forms. This makes it possible to classify materials more quickly and compare their properties more effectively.

This system facilitates communication throughout the entire supply chain—from material selection to technical implementation—particularly in the steel trade, mechanical engineering, and plant engineering.

Those who understand the logic behind the designations can market steel grades with much greater confidence and select them more effectively for specific applications.