STRUCTURAL STEELS
This is the “heaviest” steel family due to its use in larger quantities because of the applications it is designed for: trusses, large carpentry works, infrastructural works and mechanical organs of various kinds (wheels, racks). S235, S275 and S355 are the main types of steel in this family and are present on the market in all the typical formats of semi-finished products: bars of different section, sheets, tubes and profiles, in the so-called “natural” state or with subsequent normalising treatments such as annealing and stress relieving, in order to optimise the subsequent processing operations and guarantee specific mechanical performances.
FREE-CUTTING STEELS
The steels for high-speed machining, commonly called free-cutting steels, have been specially designed to be machined by chip removal with high productivity.
They are processed by machine tools for shavings removal (turning, milling, drilling, etc.).
Sulfur and lead are the elements that give these steels the peculiarity of encouraging the formation of an appropriately broken chip during processing, in order to speed up work cycles (increasing the productivity of mechanical workshops) and minimise tool wear.
11SMnPb30, 11SMnPb37, 36SMn14 and 46S20 are the main types of free-cutting steels used to make fittings, injectors, mechanical parts, small metal parts and pistons, etc.
STEELS FOR QUENCHING AND TEMPERING
Quenching and tempering are two thermal treatments that increase the mechanical characteristics of steel (tensile strength and hardness) while maintaining a good degree of toughness (i.e. to arrive at the break with a good degree of deformation and not in a fragile manner). C35, C45, 42CrMo4 and 34CrMo4 are the main types of steel in this family and are widely used in various sectors: transport, pistons, transmission parts, gears, screws and bolts, etc. The presence of elements such as chromium and molybdenum gives the steel a greater capacity to push the effects of hardening to the heart of a component, in order to obtain added resistance across the entire mass of a finished component.
STAINLESS STEELS
Stainless steels are most notable for their corrosion resistance. They do not oxidise, forming iron oxide or rust on the surface. This characteristic is conferred by chrome which must be present with a content of at least 12% to develop a thin film of chrome oxide on the surface and protect the steel from corrosion.
They are divided into 5 subfamilies, but there are three main types:
Stainless steel AUSTENITIC chrome-nickel: the progenitor is the so-called 18/10 of pans (AISI 304), which combines resistance to corrosion with excellent cold formability. These steels are non-magnetic.
FERRITIC stainless steels to chrome only: typical applications for car mufflers (AISI 409) and washing machine baskets (AISI 430). They are attracted by magnets.
MARTENSITIC stainless steels with 12% Cr: they can be hardened and tempered and applied in cutting parts (e.g. knife blades, AISI 420) and where surface hardness is required (e.g. pistons).
They are widely used in the food and catering sector due to their hygienic features.