[en] Corrosion tests for ten iron-base and nickel-base alloys at 850degC for 1000h in H₂O + SO₃ atmosphere were carried out to obtain data for selection of candidate container materials in the thermochemical process which produces hydrogen from water by use of iodine and sulfur as circulating materials. The following results were obtained: (1) Oxidation, spallation of corrosion film, uniform corrosion and grain boundary penetration composed of internal oxidation and sulfuration occur in this atmosphere and the corrosion proceeds by grain boundary penetration. (2) SUS304, SUS316 and Hastelloy C276 are inferior in corrosion resistance and SUS329J4L is superior among ten alloys used in this experiment. Alloys such as Alloy 800H and Hastelloy XR show intermediate corrosion resistance. (3) Oxide films of alloys containing iron and chromium are mostly composed of outer iron-oxide and inner chromium-oxide. Sulfur concentrates at scale/metal interfaces and grain boundary penetration portions, and sulfides form. (4) Corrosion in this atmosphere could be expressed using the parabolic law between the grain boundary penetration depth and time. It is considered that causes of the apparently observed parabolic law were a high concentration of SO₃ and change of the gas composition caused by catalytic action of the corrosion film formed with the progress of corrosion. (author)