Corrosion Resistance of Modified Heat-Treated 16Cr-4Ni Steel for Geothermal Steam Turbine Blades

Immersion corrosion tests and electrochemical corrosion tests were carried out in the simulated geothermal water on a modified heat-treated material of 16Cr-4Ni steel, which is used for geothermal steam turbine blades. Incidentally, the purpose of the modified heat treatment is for reducing the susceptibility of stress corrosion cracking (SCC) of the steel in the geothermal fluids. For comparison, a conventional heat-treated material of the 16Cr-4Ni steel was also used in the corrosion tests. In the immersion corrosion tests up to 4,000 hours, the modified heat-treated material showed lower corrosion rates than those of the conventional heat-treated one in the test water. In the electrochemical corrosion tests, the modified heat-treated material exhibited noble and stable corrosion potential behavior. The XPS analysis results exhibited that the passive films formed on the materials were consisted mainly of Cr-oxides (CrOOH, CrO3) and Fe-oxides (FeO, Fe2O3). Furthermore, the composition ratio of Cr-oxides in the outermost surface of the passive film formed on the modified heat-treated material was higher than that on the conventional heat-treated one. It was suggested that the better corrosion resistance of the modified heat-treated 16Cr-4Ni steel was contributed to the formation of the passive film with higher compositions of Cr-oxides

A Case of Unusual Polypoid Mixed Hemangioma of the Sigmoid Colon: Possibly an Angioadenomatous Polyp

Herein, we report on an unusual case of polypoid mixed hemangioma of the sigmoid colon. An 85-year-old woman who underwent colonoscopic examination was found to have a smooth, red polypoid tumor, 6mm in diameter, in the sigmoid colon. The polyp was resected endoscopically. Microscopically, the polyp contained two pathologic components: (i) adenomatous proliferative glands as the epithelial component; and (ii) mixed hemangioma as the mesenchymal component. On the basis of these findings, a pathological diagnosis of angioadenomatous polyp was made. Although seven previous cases of polypoid hemangioma located in the submucosa have been reported in the literature, the present case is the first in which the hemangioma is localized only in the mucosa. The mixed hemangioma may be the pathogen stimulating the adenomatous proliferation of the glands