An embrittlement which occurs during tempering in which a blue color appears on the surface of clean steel. Blue brittleness is caused by precipitation hardening that develops in iron and some steels over the temperature range of about 200 to 450°C (400 to 8OO0F). The severity of the embrittlement depends on the strain present in the metal prior to heating, and on the time spent in the blue brittleness temperature range.
