Effect of Grain Size on the High Temperature Oxidation Behaviour of Austenitic Stainless Steels

The effect of grain size on high temperature oxidation behaviour of 316 steels at 700º, 850º and 1000ºC in air was studied. The results show that the mass gain increases with the increase of grain size. Particularly, the gradient of mass gain is severe in at lower oxidation temperatures. In the oxidation at temperatures of more than the solid solution temperature, the grain size before the oxidation changed to coarse grain size. Therefore, in this case, it is not enough to estimate the oxidation behaviour by the grain size before the oxidation. The exfoliation of oxide scale is severe in steel with coarse grains. Over 850ºC, the exfoliation was observed in 316 steel with coarse grains. At 1000ºC, the oxide scale of 316 steel was exfoliated, but it was extreme in the coarse grains. Cr, Mn and Si in the oxide scale were enriched in the oxide scale of the steel with fine grains. Particularly, Si was remarkably enriched at the metal-oxide interface and grain boundaries.