Effect of boron on the corrosion behavior of Type 304L, 316L and high chromium stainless steels has been investigated by various kinds of corrosion tests and electrochemical measurements in H₃BO₃-Cl^- environments at 80°C. The precipitation of borides such as M₂B (M=Cr, Fe, Mo, Ni) has led to the decrease of Cr and Mo content in matrix because of the enrichment of Cr and Mo in borides. So, the corrosion resistance of boron-containing stainless steels deteriorated with increasing boron content. The corrosion resistance was dependent upon Cr+αMo content in the matrix and increased with an increase in the Cr+αMo content. The α value was related to the type of corrosion and the environment tested, and changed from 1 to 3. Carbon was a detorimental element which caused the deterioration of corrosion resistance by sensitization. 0.01% C-22% Cr-10% Ni-1.5% B steel had high corrosion resistance in H₃BO₃-Cl^- environments.

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The effects of Sn content and simultaneous addition of selected alloying elements, such as Sn and Cu, each in slight amount, on the corrosion behavior of austenitic stainless steel of Type 304 have been investigated by using mainly electrochemical means in sulfuric acid solution. The main results obtained are summarized as follows: Sn exists in the matrix in solid solution, but is absent in nonmetallic inclusions. The corrosion rate in boiling 5wt% H₂SO₄ solution was remarkably reduced by addition of less than 0.5wt% Sn to the steel, and was further reduced by simultaneous addition of Sn and Cu. The reason why Sn improved the corrosion resistance of the steel was that the cathodic reaction and the anodic dissolution reaction in the active region were retarded by the presence of the surface film formed as a result of deposition of Sn in the form of oxides, SnO and/or SnO₂. Therefore, until the film is formed on the steel surface, addition of Sn to the steel results in degraded corrosion resistance because of preferential dissolution of that element. Simultaneous addition of Sn and Cu makes the anodic reaction to retardation, and the resistance to dissolution in activated region to increase.

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A new corrosion data-base system, which is constructed with a hierarchical structure and suitable for using personal computer, is presented in this study. The system has following characteristics; (1) The hierarchically structured data-base makes it possible to treat a large amount and various kinds of corrosion data promptly and accurately even on a personal computer with a small memory space. (2) The system eliminatory an error of treating similar data to different category and vice versa so as to increase reliability. (3) It allows partial modification easily since the data file is divided into sub-data files, such as numerical data, image data and so on. (4) The system has functions of super-imposing of graphs and converting units, which make it possible to compare different graphic data.

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Protectiveness of CVD Al₂O₃ films deposited on SUS 304 stainless steel coupons precoated with CVD TiN films was studied by isothermal and cyclic oxidation tests in pure oxygen under atmospheric pressure. The deposition temperatures were 1073, 1173 and 1273K, and the oxidation temperatures were 1173 and 1273K. The adherence of the Al₂O₃ film to the TiN film is so good that the partial spallation takes place almost always at the interface between the TiN film and the substrate, The Al₂O₃ films on flat areas of the specimens are protective during the isothermal oxidation, and hence the TiN film and the substrate do not oxidize. Contrary to this cracks are developed in the films on and near the specimen edges, where the exposed substrate surface oxidizes. The degree of this cracking depends on the deposition and oxidation temperatures. During the cyclic oxidation test with a maximum temperature of 1273K, partial spallation of the film takes place over relatively wide areas when the deposition temperature was 1173K. However, when the deposition temperature is 1273K the spallation is very limited. The above observations were explained mainly in terms of the thermal stresses.

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The practical treatments of environment conditioning and inhibitors for corrosion controlling are described. It is in principle possible to prevent corrosion by the removal of corrosive agents or by the addition of inhibitive agents. Desicants are used to reduce relative humidity which is the most important factor of corrosion in gas phase. In aqueous systems the environments can be made less aggressive by removal of dissolved oxygen, adjustment of pH, or deionization. Inhibitors are classified as volatile, water soluble, or oil soluble. Environment controls to reduce corrosion in boiler water systems, cooling water systems, and petroleum refining processes are also given.

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Useful information can be deduced from images of corroded surfaces, including fracture surfaces, by a scanning electron microscope (SEM). However, such visual examinations are qualitative and subjective, though SEM images contain enormous information on operating fracture mechanisms. The application of computer image processing techniques to SEM images enables quantitative and objective assesment without human assistance. In this review, recent advances in image processing of fractography are summarized: image processing systems for fractography, region segmentation corresponding to intergranular cracking, i. e., automatic identification of intergranular cracking, and re-construction of three-dimensional topography. The results show that computer image processing techniques provide us powerful tools to clarify fracture mechanisms in an aggressive environment.

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