The high temperature (HT) ferritic stainless steels complement Outokumpu Stainless austenitic heat and creep portfolio. The main alloying element in the ferritic grades is chromium. Its positive effect on the scaling resistance is enhanced by silicon and aluminium.

The two lower alloyed grades are best suited for temperatures between 550°C and 850°C, at which most HT austenitic stainless steels are prone to form brittle phases. The higher alloyed ones are applied at temperatures up to 1150°C and show excellent resistance against reducing sulphur attacks and molten metals.

Due to their ferritic structure, the ferritic steels show lower strength at temperatures exceeding 600°C, but are more resistant to thermal shocks than HT austenitic stainless steels. With the thermal conductivity higher and the thermal expansion lower than the respective values for austenitic steels, equal thermal shocks will result in lower thermal stresses in the ferritic material. In these terms, ferrites allow greater tolerances for design and operation.

4742 shows better scaling resistance than 4724 and can be subjected to reducing sulphur environments without risk. It is subject to 475°C embrittlement and grain coarsening at temperatures above 950°C. s-phase may form after long time exposures to temperatures around 650°C.