Stainless steel

The term stainless steel is used to indicate a group of ferrous alloys containing a minimum percentage of chromium of about 12%. Other elements such as nickel, copper, silicon, titanium and molybdenum can be added to give specific physical characteristics to the steel.

In particular, the almost absence of carbon and the presence of chromium give the alloy the so-called ability to passivate itself, i.e. to cover itself with an invisible layer of chromium oxides, capable of self-regeneration, which protects the surface from the corrosive action of oxygen and other agents. Higher levels of resistance can be obtained by varying the percentages of chromium, nickel and molybdenum.

This particular feature therefore makes stainless steel an ideal material for many applications. For example, the ease with which it can be sterilized and the absence of the need for surface coatings have prompted the use of stainless steel in professional kitchens and systems for the food industry. Furthermore, stainless steel – in particular alloys belonging to the austenitic family which contain nickel – thanks to its elongation capacity can be molded in different shapes, with various degrees of complexity, such as pipes and storage tanks for chemical products and food. To date, stainless steel is used in a wide range of sectors such as medical, aeronautics, O&G, maritime, automotive and food.

To differentiate the different types of stainless steel, the notation of the American Iron and Steel Institute (AISI) is commonly used. The AISI notation identifies a specific typology with a three-digit abbreviation with the possible addition of some letters. The first of these three digits indicates the family to which the steel belongs while the letters are used to indicate certain characteristics that can be found in all families. For example, the letter “L” indicates a low percentage of carbon (Low Carbon), as “Ti” indicates the presence of titanium.

There are 5 large families of stainless steel, which mainly differ in their crystalline structure: austenitic, ferritic, duplex, martensitic and hardening by precipitation (PH).