The effect of pre-exposure on the apparent tensile strength of annealed and/or cold rolled specimens of 65%Cu-35%Zn brass, which were pre-exposed to 2.5N ammoniacal solutions containing 0-40g/l Cu for 3hr at room temperature, was examined as the parameters with respect to chemical composition of solutions, pre-strain, grain size and cold reduction.
The results obtained are as follows;
(1) The decrease of tensile strength of both annealed and cold rolled specimens due to preexposure depended largely on the chemical composition of solutions, and the maximum decrease was found when thick black tarnished layer was formed.
(2) The apparent tensile strength of annealed specimen was exceedingly decreased when the specimen was pre-strained at yield point.
(3) The apparent tensile strength of cold rolled specimen increased with pre-straining.
(4) The decrease of apparent tensile strength due to pre-exposure was nearly proportional to depth of corrosion penetration.

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The corrosion resistance of low alloy steels have been studied with particular attention to the formation of macro-cathodic area on the corroded surface. Additions of chromium to steel increase the macro-cathodic area, which effectively decreases the corrosion rate. The latter behavior cannot be explained by the “catehment area principle” which claims that the corrosion rate is constant as far as the total area for oxygen reduction remains the same. The results of polarization measurements and various corrosion tests using artificial macro-cathode show that Ca⁺⁺ and Mg⁺⁺ ions in sea water deposit on the macro-cathodic area forming an effective oxygen diffusion barrier. Thus, the beneficial effect of macro-cathodic area can be attributed to the slower oxygen reduction on such areas, the increase of which by chromium additions accordingly reduces corrosion.

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Stress corrosion cracking of SUS 304-butt welded joints in 42% boiling MgCl₂ solution was studied. The summary of this study and the results obtained are as follows:
1) Preliminary tests for welding were made in order to obtain desirable laboratory test specimens with small angular distorsion and offset. Based on these tests, conditions for welding and cutting size of plate were determined, and desirable specimens with satisfying shapes and reproducibility could be obtained.
2) Three kinds of surface finishing of test specimens, i. e., no finishing, abrasing through #1000 emery paper and grinding by surface grinder, were adopted in order to clarify the effect of surface finishing on SCC. Examination of surface roughness, residual stresses and microstructure, etc., showed that i) hot rolled specimen (No. 1 finish) had extremly roughned and hardened surface with relatively higher tensile residual stresses, ii) abrasion by emery paper developed a very smooth surface with compressive residual stresses, iii) grinding developed a sharp kerf surface with higher tensile residual stresses.
3) Constant load type SCC tests in 42% boiling MgCl₂ solution were carried out on 11 kinds of base metal and welded, specimens. As a results, it was found that both the hot rolled base metal and their welded specimens had a considerably higher susceptibility to SCC, and all failured within 500hr duration at the applied stress as low as 3kg/mm². On the other hand, 5 kinds of solution heat treated and their welded specimens exhibited proper resistance to SCC and had the threshold stresses higher than 7kg/mm². Welding operation increases the susceptibility to SCC when the base metal is solution heat treated, but decreased it when the base metal is hot rolled. Abrasion of specimen by emery paper decreases the susceptibility to SCC but the grinding extremly increases the susceptibility. It was pointed out that the grinding, as a practical surface finishing, should be rechecked because of its dangerous effects on SCC.
4) Post-weld heat treatment, as a useful method for preventing the SCC of welded joints, was studied. Quantitative relationships between the post-weld heating temperature and the relieving of residual stresses, the metallurgical changes and the SCC susceptibility were clarified. Necessary heating temperature for preventing the welded joints from SCC and/or intergranular corrosion was proposed.

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In this paper the results of the investigation on the effect of atmospheric exposure and electrolytic corrosion on the strength properties of spring materials are described. The materials tested are stainless steel, piano wire, nickel silver and Cu-Ni-Si alloys.
The decreases in strength of piano wire which were exposured at a seaside or an industrial pollution distrect are remarkable, and nickel silver wire failed by stress corrosion cracking. On the other hand, stainless steel and Cu-Ni-Si alloy have anti-corrosion propeties for same conditions.

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The effects of the composition of stainless steel on its corrosion resistance in acids, alkalis and chlorides are explained.

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