Ferritic stainless steels are, in principle, ferritic at all temperatures. They are normally alloyed with 13 – 18% chromium (though chromium content can be as high as 29%) and low levels of the austenite formers carbon and nickel. To tie up the carbon in the steel, they are also sometimes alloyed with stabilizers such as titanium or niobium.
Ferritic stainless steels, and especially high-alloyed ferritic stainless steels, tend to lack toughness at low temperatures. Due to sigma phase formation and ferrite decomposition, they may also embrittle with long exposure in the 475 – 950°C temperature range.
Modern ferritic stainless steels (e.g. type 430) have a low carbon content. Their resistance to atmospheric corrosion, organic acids, detergents and alkaline solutions is good (comparable to that of austenitic type 304L). The resistance of ferritic stainless steels in chloride containing environments and strong acids is moderate.
Ferritic stainless steels tend to be relatively weak at high temperatures. However, the oxidation resistance of type 430 is satisfactory up to 850°C and high-alloyed ferritic stainless steels such as 446 can be used at temperatures up to 1000°C.
For more information about the weldability and mechanical properties of ferritic stainless steel take a look at our Stainless Steel Handbook.