Unalloyed steel

Steel can be distinguished from alloyed and unalloyed steel. What difference this makes in the properties, and when to call steel as unalloyed, you will learn in this post. In addition, into which group one can alloy and divide unalloyed steels.

Purpose of alloys

Alloying steel means mixing the steel with other elements. The purpose of alloying is to give the steel special properties that it did not have without the alloy components. These properties are for example:

  • deformability
  • workability
  • strength
  • toughness
  • tensile strenght
  • rust resistance

Definition of carbon steel

Steel is always referred to as "unalloyed" if the additional constituents do not exceed a certain level. Unalloyed steel is therefore not free of other constituents, but contains foreign constituents only in a very small amount. To determine these quantities, a so-called melt analysis is performed. The result then shows whether it is alloyed or unalloyed steel.


elementLimit (mass percentage)
All other ingredientsmaximum 0.10

However, the following elements are excluded from these limits:

  • Carbon (important!)
  • nitrogen
  • Sulfur and phosphorus (so-called steel enemies, reduce the quality of steel even in small quantities)

Classification of unalloyed steels

Unalloyed steels can be divided into quality steels and stainless steels. Stainless steels are always alloyed steels as defined above - they contain by definition a chromium content of at least 10.5%.


Quality steels (this does not just mean unalloyed quality steels) are mostly used for special requirements where special steel properties are required. This can be either the machinability, but also the toughness or grain size of a steel. In contrast to alloyed quality steels, the unalloyed quality steels are also used for surface hardening and tempering. For alloyed steels, this is usually not done.

In the case of non-alloyed stainless steels, it is above all the special properties that are required for their use. They must either have a particularly high impact energy, a particularly high surface hardness or a particularly low content of non-metallic inclusions for use.

Special properties

The purity of unalloyed steels is generally higher than that of alloyed steels. In particular, the non-metallic inclusions are usually significantly lower in unalloyed steels.

Tips & Tricks

Whether it is alloyed or unalloyed steel, can be seen already on the basis of the composition, which appears in the name: Thus, for example, can be derived from the name X5CrNi18-10 that it is a so-called chromium-nickel steel. The DIN EN 10027 makes a more precise classification, in which both the use, the mechanical properties (yield strength) and certain additional qualities are taken into account. This results in designations such as E235JR - ie a mechanical engineering steel (E) with a minimum yield strength of 235 N / mm² and a score of 27 years

Video Board: 10. Unalloyed steel company - From Prabhupada Memories DVD 5