The most common ones are:
THE MARTENSITIC (AISI 420), hardenable by heat treatment;
FERRITIC (AISI 430) with stable ferritic structure independent of temperature;
AUSTENITIC (AISI 304 – 316) to austenitic structure stable independent of temperature.
Martensitic steels are those having indicatively a carbon content of between 0.1 / 0.50% with peaks of 1% and more, as well as a chromium content indicatively between 11 and 19%;
The strength and hardness superior distinguish martensitic stainless steels from other stainless steel families.
Some examples of uses: tooling steel (knife, scissors, scalpels, razor blade, injector for the internal combustion engine).
Ferritic steels are those having indicatively a chromium content of between 10.5 / 30% and carbon contents very low, usually below 0,1%;
Cr ferritic steel, not hardenable and general use.
Not suitable for particular mechanical stress.
It resists the action of sulfur compounds, even at medium-high temperatures.
Some examples of uses: Equipment for bars-restaurants, special for the food industry, decorative architectural elements, parts of household appliances, automotive accessories, parts of burners.
Austenitic steels are those that in addition to the chromium, by reason of the 16/28% contain nickel because of 6/32% and very low carbon contents, below 0.15%.
304 Stainless Cr-Ni austenitic, non-hardenable, corrosion-resistant. Good weldability and good resistance to intergranular corrosion. Excellent toughness down to low temperatures.
Some examples of applications: most common type, its use spans all sectors including: systems for industries: chemical, pharmaceutical, oil, textile, food, shipbuilding, equipment for kitchens, bars, restaurants, cutlery, crockery, some components for household appliances.
316 Stainless Cr-NiMo austenitic, not tempered, where the presence of molybdenum gives it greater resistance to corrosion.
Also the mechanical properties at high temperatures are better than those of types without molybdenum.
Some examples of applications: chemical equipment for particularly harsh conditions, equipment in contact with water or marine environment, equipment for photographic development, shirts for boilers, plants for chemical, textile, food, distilleries, oil, pharmaceutical, paper, plastics.