A temperature at which iron or steel assumes a bluish tint as a result of becoming covered with a film of iron oxide, typically about 300°C; frequently figurative.
Origin
Late 18th century; earliest use found in John Smeaton (1724–1792), civil engineer.
Definition of blue heat in US English:
blue heat
noun
Metallurgy
A temperature at which iron or steel assumes a bluish tint as a result of becoming covered with a film of iron oxide, typically about 300°C; frequently figurative.
Origin
Late 18th century; earliest use found in John Smeaton (1724–1792), civil engineer.