Results of thermal desorption analysis (TDA) measurement, which had been obtained on high strength martensitic steels by a research group of ISIJ, were sub-jected to peak separation by Gaussian distribution function to determine the amounts of trapped hydrogen; dislocation, grain boundary, vacancy and vacancy cluster. Then they were followed by the quantitative analysis with Fermi-Dirac statistics that contained pre-exponential factor representing entropy change. They are helpful in analyzing the hydrogen penetration behavior; effect of applied stress on hydrogen penetration and hydrogen pick-up during cyclic corrosion test (CCT).
The effect of applied tensile stress appeared uneven over trap sites. Consider-ing from Fermi-Dirac statistics, it is reasonable to conclude that the amounts of trapped hydrogen are not affected by the stress. At dislocation and grain boundary sites, their trap densities increased with applied stress and result in the apparent in-creases of trapped hydrogen.
Hydrogen penetration behavior of trap sites was fairly reproduced using error function on the pre-strained material. Further, by applying Fermi-Dirac statistics, the state of hydrogen was determined, which was comparable to the saturation in CCT exposure of unstrained material, namely hydrogen pick-up of 0.2 ppm. It cor-responds to that of 3.5 weeks exposure and almost agrees with the saturation, in the reproduced penetration behavior.

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In our previous study, the elongated bead welding with Low Transformation Temperature (L.T.T.) welding material were investigated to apply to boxing fillet welded joints used in ship’s local struc-ture. The welded joints by gas metal arc welding (80%Ar・20%CO₂ shielding gas) with LTT1 welding material of 10Cr10Ni filler metal showed sufficient fatigue life enhancing effect.
In this study, we showed that the elongated bead welding with newly developed L.T.T. welding material can enhance the fatigue life of boxing fillet welded joints even under the condition of 100%CO₂ gas shielded arc welding. That is, by using newly developed LTTB welding material of 16Cr8Ni flax cored wire, CO₂ gas shielded arc welding in all positions can be possible and the repair welded joints by 40 mm elongated bead welding with LTTB welding material showed about 4.3 times fatigue life in the case of overhead position welding and about 10.5 times and more fatigue life in the case of flat position welding compared with that by conventional welding.
In addition, the fracture toughness tests of LTTB weld metal by using the weld metal cen-ter-notched fracture toughness test specimen were carried out. It was shown that LTTB weld metal had sufficient fracture toughness.
As a result, it was shown that a fatigue life enhancing technique simply by in-house welding to re-pair the fatigue crack that generates in boxing fillet welded joints in ship’s local structure can be ap-plied to practical use.

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This paper describes the propagation characteristics of ultrasonic waves in glass flake coatings. Specimens with glass flake contents from 0 to 35 wt% were prepared and subjected to ultrasonic contact and immersion tests, and the dependence of the bottom echo height on the glass flake content was in-vestigated. It was found that at a test frequency of 5 MHz, the bottom echo height increased with decreasing glass flake content. In contrast, at a fre-quency of 2 MHz, the bottom echo height was independent of the glass flake content. In addition, the frequency of the reflected ultrasound was shifted downwards by about 1 MHz, regardless of the glass flake content or the test frequency．

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Galvanizing makes the surface of the steel products to prevent the corrosion on the steel surface, and to endure the long-term use of steel products. Generally, in galvanizing process, the steel product is dipped into the molten zinc with about 440 to 470℃ then zinc coating with about 50 to 150 μm is formed on the surface of the steel material to achieve long-term corrosion protection.
Recently, zinc coating steel structure is increasing in size therefore the size of molten zinc galvanizing bath also becomes larger and larger.
In this report, some unstable fracture examples of new galvanizing bath in first start-up operation are introduced and preventive measures against its unstable fracture are discussed. In addition, an unstable fracture example of galvanizing bath in normal operation due to earthquake is showed and also its unstable fracture prevention is discussed.

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