Ferritic steels are divided into two groups:
• those with approx. 11% to 13% chromium
• those with approx. 17% chromium (Cr)
Chromium steels from 10.5% to 13% are termed low-corrosion products due to their low chromium content. They tend to be used where the emphasis is on durability, safety and low maintenance requirements with no real demands on visual appearance. This is the case, for example, in container, railway wagon and vehicle engineering.
Austenitic stainless steels
Austenitic stainless steels, also referred to as CrNi steels, which have Ni contents of more than 8%, are a highly favourable choice when it comes to workability, resistance to corrosion and mechanical properties. The high corrosion resistance is the most crucial property of this kind of stainless steel. This is why austenitic stainless steels are used in environments where there are aggressive media – which is why it is used, for example, in contact with seawater containing chloride, or in the chemicals and food processing industries.
Austenitic-ferritic steels are often termed duplex steels due to their dual microstructures. The high ductility combined with the improvement in corrosion resistance means these steels are the preferred choice in offshore engineering.
Martensitic stainless steels
Martensitic stainless steels, which have a chromium content of 12-18% and a carbon content of over 0.1%, become austenitic at temperatures above 950-1050 °C. Rapid quenching forms a martensitic microstructure. This structure, in particular when it has been quenched and tempered, exhibits high strength, and this can be boosted even more by increasing the carbon content. These steels can be used for manufacturing razor blades, knives and scissors. A precondition for sufficient corrosion resistance is that the surface has the right finish, which can be achieved by grinding, amongst other methods.