Together with these corrosive influences, changes in the metal matrix can occur under certain conditions. These can have a great influence on the durability of the metals.

475 °C - Embrittlement

On long-term heating of chromium steels (> 12% Cr) in a temperature range from 400 °C to 550 °C, the steels become brittle as a result of the short range order reactions.

Sigma phase embrittlement

In steels with more than 13% chromium, the sigma phase can arise in a temperature range from approx. 600 °C to 800 °C. The sigma phase consists of 50% Fe and 50% Cr. The formation of the sigma phase is enhanced by alloy components such as molybdenum, titanium and silicon.

Carburisation

The attack is mostly made by gaseous carbon compounds which react with the constituents of the alloy. The resulting carburisation generally leads to a reduction in the ductility of the metal matrix.