In-situ acoustic emission (AE) and Raman measurements, focusing on the adhesion of a protective
oxide scale, were conducted to clarify the breakaway behavior under cyclic condition. The AE
measurement showed that the scale failure such as spalling and/or cracking occurred even after one
cycle of 3 hr heating at 1173 °K. It was also clarified that the scale stress without the creep-deformation
and spalling corresponded to calculated thermal stress. The critical adhesion force of the scale on 25Cr-
20Ni steel heated for 3 hr at 1173 °K was estimated to be 1.7± 0.2 GPa in the range of 573 °K (-?T =600
°K) to the room temperature. Cyclic heating accelerated the spalling of the oxide scale, resulting in
gradual degradation of protective oxide scale. These processes have induced breakaway oxidation of
austenitic stainless steel.