Stainless steel

Stainless steel is a common term for steel types, which contains more than 12% chrome. By further adding other alloying elements, nickel, molybdenum, carbon, nitrogen, manganese, silicon, titanium, etc., a large number of steel types have been developed, each of which is characterized by specific properties with regard to corrosion resistance, mechanical strength, weldability and formability.

The chromium content causes the steels to form a very thin passivating oxide film, which makes the steels resistant to a neutral oxygen-containing environment. On the other hand, most stainless/rust-resistant steels are not resistant to acid og seawater, and usually not salt either.

Steels are usually divided according to their microstructure, which is crucial for their mechanical properties. The following main types are distinguished:

Ferritic stainless / rustproof steel. The simplest and cheapest types of stainless steel. Has mechanical properties similar to unalloyed / low-alloyed steel. Typically chosen where good corrosion resistance is desired at a reasonable price. For example. AISI 430 and 440.

Martensitic stainless steel. In the same family as the ferritic stainless steel types, but with a higher carbon content, which makes it possible to harden the steel. Can be hardened and possibly tempered to very high hardnesses and reasonable toughness. Often used where corrosion resistance and wear resistance are important, such as knives and other cutting tools. For example. AISI 410 or 420.

Ferritic-austenitic stainless steel (Duplex steel). Duplex The steels have a mixed structure consisting of ferrite and austenite (approx. 50/50). In general, duplex steels have higher strength than both ferritic and austenitic steels, as well as excellent toughness. They have excellent fatigue strength due to the mixed structure (does not easily metal-weary). Like the austenitic steels, they are weldable.

The steels are most often named after EN standard (DIN), AISI or USFor example, “ordinary” austenitic stainless steel is referred to as EN 1.4301, AISI 304 or S30400.