In the crevice corrosion of commercially pure titanium in hot saline water, the effect of gasket materials and the coupling with dissimilar metals, e. g. with copper alloy or mild steel, has been studied and the mechanism of crevice corrosion was discussed. Titanium crevice specimen with the gasket of dimethacrylate resin was more susceptible to crevice corrosion compared with specimens with PTFE and rubber or without gasket. A role of dimethacrylate in crevice corrosion seems to be attributable to the formation of more tight crevice.
The results of potentiostatic electrolysis for titanium crevice specimens revealed that the crevice corrosion occurred at potential more noble than about -0.4V (SCE). Therefore, titanium crevice specimen coupled with copper alloy and mild steel were immune to crevice corrosion because corrosion potentials of these couples are less noble than -0.4V.
It was clarified that passive film thickness of titanium decreased markedly with lowering solution pH to the depassivation pH of titanium. On the other hand, pitting potential of titanium was about 5 volts (SCE), regardless of the solution pH and so titanium would be hardly subject to pitting corrosion even in low pH solution.
These results suggest that crevice corrosion of titanium is caused by not pitting corrosion but by active corrosion in the crevice.

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Based on the stand-point that the SCC susceptibility of prestrained member should be evaluated by the quantitative analysis of the stress states such as the residual stresses of prestrained condition and the actual stresses under applied stresses, in stead of the apparent applied stresses which were often used in the previous studies, SCC tests of austenitic stainless steel SUS 304 which were abraded with grit paper or eletcropolished and then tensile prestrained up to 20% were carried out in boiling 35wt% magnesium chloride solution.
It was made clear that the surface finishing had great influence on the variation of residual and actual stresses of prestrained specimens, however the SCC susceptibility could be evaluated by the threshold actual stresses at the surface of prestrained specimens.
Results obtained are summarized as follows.
1) Tensile prestraining of electropolished stress-free specimens resulted in the residual stress states where the equi-biaxial stresses were compressive of about -10kg/mm². The actual stresses at the surface of prestrained specimens under applied stresses could be expressed by the resultant stresses of residual and applied stresses. The apparent threshold applied stresses for SCC increased with the plastic strain, however the threshold actual stresses for SCC were constant at 20kg/mm² for all specimens prestrained up to 15%.
2) Tensile prestraining of abraded specimens which had biaxial residual compressive stresses of -30kg/mm² resulted in the residual stress states where the axial stress was tensile of 10kg/mm² and the transverse stress compressive of -15kg/mm². Therefore specimens prestrained above 10% underwent SCC without applied stresses. The actual stresses at the surface of prestrained specimens under applied stresses could not be expressed by the resultant stresses, and showed complicated behaviour. The threshold actual stresses for SCC was, however, constant at 10kg/mm² for all specimens prestrained up to 20%.
3) The surface actual stresses of prestrained specimens could be an effective parameter for the evaluation of SCC susceptibility of prestrained SUS 304 in 35wt% MgCl₂ solution.

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Developed was a new method to control stress corrosion cracking (SCC) of weldments, named PWC (Post Weld Cooling) method. In applying PWC method to butt-welded pipes, the welding joint is cooled by water from its inner side alone immediately after all the welding works are finished. SCC can possibly be controlled by the method, because residual tensile stresses in the weldment are suppressed and, in some cases, converted to compressive stresses.
The details of adequate practices of PWC method were determined and the superior immunity from SCC of the weldment treated by PWC method as compared with those made by several conventional methods was evidenced by the following two tests. That is, the residual stress measurement by X-ray diffraction method and the SCC tests in the boiling 30wt% MgCl₂ solutions were performed on the welded test-pipes which include those in as welded conditions, those with PWHT applied and those made by the Heat Sink Weld method as well as those made by PWC method.
It proved that the susceptibility of the weldments to SCC was affected by the biaxiality of residual stresses and how to evaluate the biaxiality was discussed.
The following results were obtained;
1) Residual stresses resulted from the temperature difference between the inner and outer surfaces are considered to be prevailing in the weldments treated by PWC method.
2) It is possible to induce compression as far as the weldment is cooled by water before the temperature difference between the inner and outer surfaces becomes smaller than the value which produces the thermal stress equal to the proof stress of the base material.
3) PWC method has proved as effective in controlling SCC as the Heat Sink Weld and characterized by the following items:
i) No additional care for welding before applying PWC method is required other than the conventional one.
ii) More efficiency in welding procedure will be attained because high heat input and high welding speed are recommendable and the weldment can be cooled down to the ambient temperature as soon as the welding work is completed.
iii) It does not cost too much because no special equipment is used.
iv) It is applicable to weld repair, too.
4) Biaxiality of residual stresses, which depends on the pipe-size, affects on the mode of cracks. Cracks are parallel to the welding line in the small-diameter (1B) pipes whose stress condition is σ₂<0<σ₁, while they are perpendicular to the welding line in the large-diameter (900∅) pipes, in which σ₁>>σ₂. Cracks are network-like in the medium-diameter (4B, 12B) pipes, in which σ₁≈σ₂.
5) The threshold stresses for SCC is ruled by the equivalent stress difined in the Total Strain Energy Theory.

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Relation between the corrosion rate and the shape of the potential response curve to an applied current step has been investigated for mild steel immersed in tap water as well as underground water. It was found that the potential response curve approached a straight line as the corrosion current density decreased, when the corrosion potential was more noble than -0.44V vs. SCE. In this case, it was also found that logarithm of the corrosion current density was proportionalto logarithm of ΔE₄/ΔE₁₀ in the corrosion current density range from 0.69μA/cm² to 27.2μA/cm², where ΔE₄ and ΔE₁₀ are overvoltage at 4 seconds and 10 seconds after application of current step. Corrosion current densities determined from ΔE₄/ΔE₁₀ values by the use of the regression equation agreed within 29% with those determined by the weight loss measurement. The surface state of the electrode was discussed and it was concluded that the electrode was in the active/passive transition region when the above dependence of ΔE₄/ΔE₁₀ values on the corrosion current densities existed.

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Microcomputer systems to measure repassivation potential, E_R, for crevice corrosion have been developed as reported in our previous paper. Cyclic polarization procedure to drive the systems was experimentally determined with the metal/metal-crevice of Type 444 steel in 3% NaCl solution at 25°C. Standard procedure to be recommended regards it of major importance to run electrode potential with sufficiently low sweep rate slower than 10mV/60min at the later part of repassivation stage. The E_R values thus obtained do not depend on maximum penetration depth as an extent of preceding growth of crevice corrosion, but reflect geometrical size as well as composing material of crevices. These facts confirm that the concept of E_R as a crevice characteristic can be applied also to ferritic stainless steel. Type 444 steel shows markedly more noble values of E_R than Type 316 steel in solutions containing low concentration of NaCl at 80°C.

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Materials and techniques used in Japanese traditional metal arts and crafts were examined from the standpoint of modern science. Surface finishings reviewed are;
(1) Polishing, (2) Roughening or Patterning of metal surface, (3) Fire-gilding with gold amalgam, (4) Coloring.
It is concluded that Japanese traditional techniques in metals arts are excellent in ornamenting the metal articles and even suggest some ideas that are applicable to modern technology.

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