The surface degradation of metals such as boiler tubes and turbines in high temperature corrosive environments has caused a severe problem in fuel combustion power plant systems. Many researchers have been investigating developments of thermal and corrosion resistant materials and behaviour of the materials on high temperature corrosion/oxidation [1], [2], [3] and [4]. It is well known that oxidation films once formed protect metal surfaces by forming diffusion barriers to oxygen. However, damage to materials has been often accelerated by mechanical removal of oxide films formed on the material surface. Few investigations of the acceleration mechanisms exist [5] and [6]. It is anticipated that properties of the corrosion product such as oxide films are different between high and low temperatures, although some research papers on mechanical properties of the oxide films can be found at room temperature [7]. It is therefore very important to investigate mechanical properties and adhesion of corrosion product films in practical high temperature environments, in order to discuss the acceleration mechanisms and life time of materials.