Ferritic stainless steel
Ferritic stainless steel typically contains 12-18% Cr, a low amount of Ni and a low amount of carbon (C ≤ 0,12). The ferrites have the same structure as black steel but due to the low carbon contents, they are not hardenable. It is relatively soft but has a poorer toughness compared to austenitic steel. Ferritic steel can be cold deformed but not to the same degree as the austenitic “bubble gum” steel. The stabilised types are weldable (the 45XX types) and all of them are heavily magnetic.
The lowest alloyed (e.g. 4003) have relatively poor resistance to corrosion (especially in acid), while the higher alloyed (e.g. 4521) is comparable to acidproof steel regarding pitting corrosion and partially crevice corrosion. Additionally, ferritic steel is far superior compared to austenitic steel regarding the serious stress corrosion.
Due to the low content of nickel, the ferrites are relatively cheap and are increasingly used for purposes where the formability and weldability of the austenitic steel are irrelevant or when a beautiful and magnetic surface is desired, for instance, refrigerator doors, kick plates or door handles. For the same reasons, the global consumption of the ferritic stainless steel types is significantly increasing.
Moreover, ferritic steel has major possibilities regarding heated components where there is a risk for stress corrosion in both regular and acidproof stainless steel types and also where thermal conductivity is required, which is better compared to the austenitic steel. The thermal longitudinal expansion corresponds to that of black steel which is roughly 2/3 of that of austenitic steel.
Ferritic stainless steel can advantageously be used for materials with thin castings, high material costs, and simple processing. This Syrian produced jug is made of 4016 (AISI 430) which is a widely used material in the catering industry. This is, by the way, a fantastic example of the fact that ferritic stainless steel can be deep drawn.