The investigation of hydrogen diffusion in low-alloyed high strength steels, martensitic and ferritic stainless steels subjected to heat treatments was carried out at room temperature in an attempt to establish the effect of quenched and tempered microstructures on diffusivity and hydrogen content by means of electrochemical permeation technique.
The diffusion coefficient and the hydrogen content vary with the structure of the steel. The dependence of hydrogen diffusion on the quenched and tempered structure can be explained by postulating that both the lattice imperfections, such as dislocations, faults and subgrain boundaries etc., introduced by the martensitic or bainitic transformation and/or by precipitation of coherent carbide particles during tempering, and the interfaces between the ferrite phase and carbide precipitates, provide regions for the occupancy of hydrogen.

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A differential method for measuring the number of component atoms in surface atomic layers by use of AES and argon sputter-etching was applied to the analyses of thin anodic oxide films formed on Fe-30Cr alloy, 304- and 316-stainless steels in deaerated 0.5M sulfuric acid solution. From the measured composition profiles in depth, the surface excess, Γ_Cr, Γ_Ni, Γ_O and Γ_S on the dividing surface with Γ_Fe≈O was estimated as a function of anodic potential.
In the passive potential region, the surface excess changes depending on the species of alloys as follows: Γ_Cr=1-3×10¹⁵ atoms/cm², Γ_Ni=4-8×10¹⁴ atoms/cm², Γ_O=3-6×10¹⁵ atoms/cm² and Γ_S=2-8×10¹⁴ atoms/cm². The surface excesses of chromium and oxygen, Γ_Cr and Γ_O of 316 stainless steel are smaller than that of 304 stainless steel, indicating that molybdenum affects Γ_Cr and Γ_O. The effect of molybdenum on Γ_Cr and Γ_O was discussed in connection with the electrochemical characteristics of molybdenum during passivation.

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Various experimental techniques, such as the potentiostatic and the potentiokinetic polarization charachteristics measurements, the colorimetric analyses of dissolved alloy constituents and the electron microscopic observation, were adopted to study the anodic corrosion of high nickel alloys in 1N sulfuric acid. Hastelloy B, which was the lowest in chromium content among five sorts of alloys used, showed no indication of passivation but poor corrosion resistance in the potential range investigated. Other four alloys passivated at the potential around 200mV vs. S. C. E., and the higher chromium content resulted in less passivatiog current in general tendency. These observations led the conclusion that chromium played essential role in the passivation of the alloys. In the potential range around 600mV vs. S. C. E., selective dissolution of moybdenum was observed with two sorts of alloys, namely Hastelloy C was the most remarkable in this behaviour and Hastelloy X less but slight. Localized attack was found surrounding the deposit of chromium carbide. The control of chromium depletion due to the decrease of carbon content or the increase of chromium content in alloy seemed to be effective in prevention of such selective attack of molybdenum.

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This article is a review of recent literature on corrosion inhibitors for copper and copper alloys. Inhibitors are divided into two categories; (i) inorganic inhibitors, such as chromates, phosphates, and ferrous ions and (ii) organic inhibitors which include heterocyclic organic compounds, i. e., benzotriazole (BTA) and mercaptobenzothiazole (MBT) and their relative compounds. At present these are the most effective and widely used inhibitors in a variety of systems. The BTA derivatives such as tolyltriazole (TTA) and benzotriazole carboxylic acid will be the most promising inhibitors for copper and copper alloys. It is suggested that dimercaptothiadiazole (DMTDA) and triazinedithiol (TDT) and its derivatives may be used as a substitute of BTA. Effectiveness of both DMTDA and TDT is found to be better than BTA in some corrosive environments. Significant role of oxide films present on the metal surfaces is stressed in order to clarify the mechanism of protection performance of inhibitors. Long chain thio-compounds as film forming inhibitors are also described

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