FeB is a soft ferromagnetic compound that becomes paramagnetic above ~325 °C (617 °F). In air, FeB powders begins to react with the ambient oxygen above 300 °C, though bulk FeB materials are expected to be stable in air to much higher temperatures. FeB is an extremely hard compound (15-22 GPa as measured by Vickers indentation), but is not sought after on borided steels because FeB layers are brittle and prone to spalling off the steel or iron.
