The failure of oxide scales formed on mild steel (mass contents of 0.17% C,
0.13% Si, 0.72% Mn) was investigated using a high-temperature tensile test
technique over the temperature range 830 - 1150 degrees C. Strain and stra
in rates used were 1.5 - 20% and 0.02 - 4.0 s(-1), respectively. The scales
were 10 - 300 mu m thick. The variations of these test parameters were cho
sen to approximate the tensile loading of the oxidised surface layer at the
slab faces just before roll contact at the upper or lower surfaces. Oxide
scales formed cannot be assumed either to be perfectly adhering during tens
ile loading, in the sense of slipping, or to be fully brittle. Two limit mo
des leading to oxide spallation have been observed which are strongly influ
enced by the temperature, strain rate and strain. For the first mode initia
l through-scale cracking occurs followed by initiation and propagation of a
crack along the oxide-metal interface between adjacent cracks. The second
mode corresponds to the slipping of the oxide scale relative to the metal s
urface before spallation. The delamination and following slipping of the ox
ide raft can take place along the interface within the non-homogeneous oxid
e scale.