„May the steel be high-grade, rustproof and good“
Overview of the material.

The metal generally referred to as high-grade steel, stainless steel or (expressed academically) „rustproof and acid-resisting steel“ has been around for almost 100 years. Its industrial use began in 1912 when the patent application was submitted for steels with “high resistance to corrosion”. These humble beginnings have led to the development – particularly since 1950 – of a materials group comprising more than 120 stainless steel types that are used in every segment worldwide.

What makes stainless steel so resistant?
A common feature of all stainless steels is that their steel alloys contain a chromium element of at least 12%. The contact with the oxygen in the surrounding media (air, water, other substances) leads to the formation of a thin – only a few atom layers – transparent layer of chromium oxide (passivation) on the steel surface. This layer protects the steel beneath it from further chemical influences. If the surface is damaged this passive layer rebuilds itself autonomously under the influence of oxygen; for this reason we can justifiably call it a “self-healing “ or “self-repairing mechanism”.

Understanding this process is important for, among other things, the use of stainless steel in lowoxygen or oxygen-free environments; here there can be no subsequent passivation of the surface and the material is exposed to the aggressive influences.

The addition of other alloying elements further improves the mechanical and chemical properties of stainless steel: nickel increases the resistance to acid and is contained in all commonly used stainless steels; sulphur improves the machining qualities (A 1); titanium, niobium or tantalum stabilizes the material structure at higher temperatures (A 3 and A 5); manganese, molybdenum and copper are other commonly used alloying elements that increase the resistance to reducing acids and localized corrosion. (You can find details of the chemical compositions in the overview on page 521.) Once the right types of stainless steel for the individual application case have been chosen, nothing can stand in the way of a long lifespan and therefore a secure fastening element.