Thermal diffusivities of oxide scales on iron-base binary alloys and steels

Abstract

The thermal diffusivities of oxide scales on iron, certain binary iron alloys, and selected commercial steels have been determined in situ at temperatures from 473 to 1273 K with a laser flash-pulse technique. The results confirmed that the thermal diffusivities were a function of the type of oxide and of its growth morphology. The greater the proportion of magnetite (Fe₃0₄) and free iron in a scale, the higher is the thermal diffusivity obtained (up to ∼ 9 x 10⁻⁷ m² s⁻¹). A scale/metal interfacial gap constitutes a thermal barrier possessing a correspondingly lower apparent thermal diffusivity (<1 X 10⁻⁷ m² S⁻¹). Consideration is given to the practical problem that the cooling rate for a blistered, scaled surface may be a factor of 5-50 times slower than that for a descaled steel surface.