What is steel actually?


Of course everyone knows the term steel - but what is technically exact in terms of steel is a bit more complicated. Which technical definition applies to steel, how it can be distinguished from other types of metal, and how steel is constructed exactly, you will learn in this article.

Definition of steel

Steel today is available in an incredibly large number of alloys, with a total of well over 5,000 different alloys. They can be quite differently structured, the similarities between all steel types are only small. Steel can only be defined as:

Alloys whose main component is iron, and which can be processed by forming processes. Forming processes include rolling or drawing.

Distinction to the cast iron

Cast iron also has iron as its main component. However, cast iron can not be processed by reshaping, which makes the definition of steel technically possible. Typically, cast iron also has a comparatively high carbon content, generally above 2.06%. Again, there is a distinction between cast iron and steel.

This distinction also applies to DIN EN 10020, although it does remove certain chromium steels whose carbon contents are higher. They are still considered as steel and not as cast iron.

Effectiveness of the definition

For most steels, the definition of DIN is still applicable, but there are already special steels where this very general definition no longer applies. However, these are only a few alloys that represent special cases.

Construction of steel

Steel is a mixture of metals and nonmetals, the structure of which can be very different. This is called the "structure". Upon cooling after melting, the iron atoms form crystalline structures which, upon complete cooling, collide and are held together by chemical metal bonding.

Depending on the cooling rate, alloy and other factors, different microstructures form. It is thus possible to distinguish between austenitic and ferritic steels, in the mixed form, where both microstructures occur in steel, the term duplex steel is used. By particularly rapid cooling you can create the popular (because very hard) Martensitic structural components. It is also possible to subsequently transform austenitic structures into martensitic ones, thus significantly altering the steel's properties.

Properties of steel

Due to the high number of alloys used, the technical properties of steel are completely dependent on the respective alloy and the method of production. There are hardly any common properties, also typical material properties such as magnetizability, melting points or other technical properties. Only the density of steel is in a very narrow range, namely between 7,850 and 7,870 kg / m³.

Tips & Tricks

Important to identify a type of steel are the standardized designations, but most of all the so-called material number. It clearly states the respective steel grade, so that one can look up the exact properties in an overlay.


Video Board: When was steel invented? and the MAGIC SWORDS of ancient times