Stainless steel is an alloy of iron, chromium and carbon, sometimes supplemented by other elements, mainly nickel.
It is the addition of chromium that gives these steels the properties of stainless steel. In oxidising media such as air, chromium forms a very thin and compact oxide layer that protects the material from corrosive attack. Stainless steels are classified according to the different elements and the relative amounts of each of them in their composition.
In general, there are four basic families of stainless steels: martensitic, ferritic, austenitic, duplex and precipitation hardening (PH).
Austenitic
These are alloys consisting of iron, chromium, nickel and carbon. The addition of nickel modifies the structure of these materials. It is the group of stainless steels with the best properties from the point of view of component and equipment manufacture, and also in terms of performance in use. They have excellent forming properties, good weldability and high resistance to different types of corrosion. Examples include 201 stainless steel, 301 stainless steel 304 stainless steel and 316L stainless steel alloys.
Ferritic steels
Ferritic steels are also alloys of iron, chromium and carbon and have a higher chromium content and lower carbon content than martensitic steels. Typical values for these elements are. C < 0.12%; Cr 16-18% (409L stainless steel, 430 stainless steel, Type 441 steel).
Martensitic
These stainless steels are an alloy of iron, chromium and carbon with typical contents of C: 0.15% and Cr: 12-15%.
These steels undergo structural changes as the temperature rises, so they are usually subjected to quenching and tempering heat treatments.
After these processes, they achieve good mechanical properties and are sufficiently corrosion resistant. They are mainly used for surgical instruments and cutlery (410 stainless steel sheet, 420 stainless steel sheet, 440A steel).
Duplex
Duplex stainless steels consist of two phases in their microstructure: ferrite and austenite. They contain alloying elements such as iron, chromium, carbon and nickel, the last in a lower proportion than austenitic steels.
In general, they have better mechanical properties and corrosion resistance than ferritic and austenitic steels (e.g. steels 2001, 2304, 2205).
Precipitation hardening (PH)
This type of steel provides an alternative to austenitic stainless steels when a combination of high mechanical strength and workability is required. They are Fe-Cr-Ni alloys characterised by mechanical resistance and hardening obtained by thermal ageing treatment (e.g. 17-4PH, 17-7PH).
At Tisco steel, we offer you the best quality stainless steels in flat, sheet, coil or strip, in a wide range of alloys.
Austenitic
Martensitic
Ferritic
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