Steel or stainless steel?

The distinction between steel and stainless steel is not always easy. Above all, the colloquial categories do not correspond to the technical ones - here there are deviations. What exactly steel and what is now stainless steel, you will learn in this post.

Technical definition of steel

Steel is technically very difficult to define because there are over 5,000 steel grades (alloys) that can have completely different properties due to their different composition. (How to group them together is summarized in this article).

Basically, one can interpret a definition of steel as meaning that it is an alloy whose main constituent is iron and whose carbon is below 2.06% (cast iron has carbon contents above 2.06%).

Although a few steel grades are no longer covered by this definition, these are only a few varieties with a higher carbon content.

Technical definition of stainless steel

Technically speaking, stainless steel is just a steel with a particularly high degree of purity. It does not matter which type of alloy it is. Technically speaking, every very high purity steel is a stainless steel. This has nothing to do with other alloy properties.

Particularly important is a low level of sulfur and phosphorus. Both are considered as "iron accompanying substances" and generally have negative effects on the performance properties of a steel. For a steel to be considered stainless steel, sulfur and phosphorus must not exceed 0.025% (mass percent in the alloy).

stainless freedom

Occasionally, stainless steel is confused with so-called stainless steel. That is a mistake. The term stainless steel refers to the purity of the steel, stainless steel, however, is only a steel, if it has at least 10.5% chromium content in the alloy. If other ingredients are included, such as nickel, molybdenum and manganese, then the corrosion resistance of the steel will increase.

The steel grade number in the material number indicates which steel grades are stainless steels, and which alloy them, and which are unalloyed. The steel grade number is the first digit pair after the 1st of the material number.

Unalloyed stainless steels have numbers 10 - 18 (eg 1.10xx.x)
Alloyed stainless steels have the numbers 20 - 89 (eg 1.20xx.x)

Tips & Tricks

A slightly less high-quality group are the so-called quality steels. The least quality is mass steel or structural steel.

Video Board: The Four Types of Steel (Part 4: Stainless Steel) | Metal Supermarkets