This paper shows the outline of steel framed houses and the promotion activities by the Kozai Club. Steel framed houses, in which galvanized thin steel plate shapes were used in stead of lumber to the framing materials used in two by four lumber houses, were originally developed in the U.S.A. Recently, because of the increase in lumber cost and the quality of lumber needed, steel framed houses have caught much attention, and already have a sufficient share in the market in the U.S.A. In Japan, after the Great Hanshin earthquake, as steel framed houses were built for the temporary houses, construction of steel framed houses had already begun, and it is estimated that future development will continue because of the saving of forest resources. This paper shows the researches for steel framed houses by the Kozai Club, and the targets and problems in the promotion of steel framed houses.
Slurry erosion rates largely depend on the conditions of solid particles' impact such as the impact frequency, velocity and angle. Even a slight difference between conditions in the testing apparatus and those in an industrial machine will cause disagreement in the damage mechanism and the test results of candidate materials in the apparatus will not agree with their performance in the field even in a qualitative comparison. The only resort is to conduct material tests under clear impact conditions and to estimate their performance in the field by comparing the impact conditions of the spheres. In this study, the numerical analysis was conducted on the particles' impact conditions in a jet-in-slit apparatus, and the results were compared with those which were determined by experimental measurements such as the size, shape and number of craters formed on the specimen surface. Lastly, the erosion rates estimated on the thus determined impact conditions were compared with experimental measurements to obtain an excellent level of agreement. In conclusion, the solid particles' impact conditions in the jet-in-slit testing apparatus were clearly determined.
The most remarkable feature of the jet-in-slit apparatus for the slurry erosion test is that the solid particles impinge at various angles different from place to place on the specimen surface. Still, as the exact impact angle at any one place on the surface has been already determined, the impact angle dependence of erosion rate can be easily investigated by measuring the erosion depth distribution over a single specimen surface. Using the test apparatus, the feasibility of ceramic coatings as slurry erosion-resistant material was elucidated. As a result, it was revealed that ceramic coatings have good erosion resistance as compared with metallic materials at shallow impact angles; the order of erosion resistance in three kinds of ceramic coatings was chromia>alumina>zirconia. The same order of performance was obtained in a rotating disk type apparatus which simulates pump impeller erosion.
Cast austenitic stainless steel, such as SCS 13, which consists of δ/γ duplex phase, is extensively used as structural material in seawater environments. However, it undergoes pitting corrosion under certain conditions. In this paper, effects of δ ferrite on the pitting corrosion are discussed in terms of microstructure of the material. The corrosion behavior of the materials with different δ ferrite contents and cleanlinesses have been evaluated by seawater exposure testing, electrochemical polarization, and TEM-EDX analysis. The results indicate that pits mainly nucleate at nonmetallic inclusions such as MnS and δ/γ boundaries. The nucleation at the latter sites is assumed to be due to the segregation of P combined with Mo and Cr. The segregation is suppressed for materials containing δ ferrite above 6vol%, and such materials are highly resistant to pitting corrosion.
The competition concept states that stress corrosion cracking (SCC) can only occur when the crack growth rate exceeds the dissolution rate; moreover, based upon this concept, that there also exist a critical temperature for SCC of austenitic stainless steels in chloride solutions which SCC can not occur at or below this temperature. The objective of this study is to explain both the observed SCC potential region and the SCC critical temperature obtained for 18Cr-14Ni steels by referring to the competition concept. The SCC potential range was found to be the potential range between the crevice repassivation potential and the potential where the crack growth rate equals the dissolution rate. The SCC critical temperature was found to be the temperature where the crack growth rate and the dissolution rate intercept in an Arrhenius plot. Thus, this study has confirmed the applicability of the competition concept in determining the stress corrosion cracking behavior of austenitic steels in chloride solution.
Tinplate has been widely used for can container. However, as the can manufacturing method had been rapidly changed from soldered can to welded can, superior lacquer adhesion was strongly required to manufacture lacquered can body and can end. A study about the cathodic treatment in the chromic acid and sulfuric ion bath was carried out to improve the lacquer adhesion of tinplate. It revealed the following facts: The cathodic treatment greatly improves the lacquer adhesion of tinplate when the chromium coating weight exceeds 20mg/m2. This fact results from the increase of chromate layer coverage on the tinplate surface, which was quantitatively measured by CMA mapping method. As for the structure of chromate layer, the deposition of metallic chromium inside is essential to suppress the growth of tin oxide.
Perforation of 5.5mm thick type 316L austenitic stainless steel (SS) weldments in industrial water containing sulfate-reducing bacteria (SRB) has occurred from internal pitting corrosion in as little as four months after operation. This piping system was operated every one month with low flow rate of 0.44m/s. Results of failure analyses have demonstrated that the preferential attack of austenite leaving δ-ferrite was observed in the pitting at the leak location. The pitting was full of deposits insoluble in water containing significant levels of sulfur as sulfide and chloride. It was thought that SRB in industrial water reduced SO42- to HS-, this was subsequently oxidized to S2O32- during the period of shutdown allowing oxygen to enter the system. The severe corrosion was believed to be the result of S2O32- production which can enhance cathodic reaction, with a resultant increase in anodic dissolution of SS.