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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 98 (2012), No. 4

  • Adhesion of Microorganisms on the Surfaces of Various Metallic Materials Immersed in a Cooling Water Tank of the Package Type Cooling Tower

    pp. 109-116

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    DOI:10.2355/tetsutohagane.98.109

    Adhesion of microorganisms and biofilm formation on the surfaces of some single alloys and plated steels were evaluated in order to estimate the inhibition capability against biofilm formation on these materials. SS400, 304 steel and 430 steel were used for test materials. Ag, Co, Cr, Cu, Ni, Sn and Zn plated steels were also used for test materials, respectively. These specimens were immersed in a cooling water tank of the package type cooling tower for 1 month. Surface observation was carried out before and after immersion test to evaluate inhibition capability against biofilm formation. The chemical composition on the surface of each specimen was also evaluated, because of various elements such as Ca, P and Si are concentrated in biofilm during immersion test.
    Adhesion of algae and extraneous matters were observed on the surface of each specimen after immersion test. The extent of increase in Ca content and adhesion of algae on the surfaces of 304 steel, 430 steel, Cr plated steel and Ni plated steel were lower than those of SS400, Ag plated steel, Co plated steel, Cu plated steel, Sn plated steel and Zn plated steel. The results for SS400 and the specimens with plated layer composed of noble elements such as Ag, Co, Cu and Sn show lower inhibition capability against biofilm formation, indicate that the iron ion was involved in biofilm formation. 304 steel, 430 steel, Cr plated steel and Ni plated steel showed higher inhibition capability against biofilm formation in this study.
  • Effect of Nitrogen on Creep Rupture Strength and Toughness After Aging of an Austenitic Heat Resistant Steel

    pp. 117-124

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    DOI:10.2355/tetsutohagane.98.117

    Creep-rupture tests and Charpy impact tests after long-term thermal aging were performed for three austenitic heat-resistant steels of which compositions were Fe-25%Ni-23.5%Cr-1%Mo-6%W-(0.11 to 0.27)%N-0.05%Ti-0.20%V-0.25%Nb-0.004%B by wt% to reveal the influence of nitrogen contents on the mechanical properties required for boiler tubes. Creep-rupture strengths of the steels at 700 °C for 6000 h were higher than 155 MPa. The material which showed the highest strength at 700 °C for 6000 h was the 0.21N steel. Nitrogen in the steels contributes to increasing the creep-rupture strength. The effect of nitrogen under higher stress condition became larger while the effect became smaller under lower stress condition. It was supposed that nitrogen decreased the effect of precipitation strengthening by stabilizing the austenite phase for a longer time while it increased the effect of solid solution strengthening. On the other hand, the Charpy impact value of all steels after aging at 700 °C for 1000 h became less than 10 J/cm2. Nitrogen in the steels did not have a notable influence on the toughness after long-term thermal aging because precipitates of M23C6 and a tungsten-rich phase formed along grain boundaries deteriorated the toughness.
  • Effects of Strengthening Factors on Tensile Strength of Warm-Worked Middle Carbon Steels

    pp. 125-134

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    DOI:10.2355/tetsutohagane.98.125

    The purpose of this research is to clarify the effects of strengthening factors on tensile strength of warm-worked middle carbon steels. The increase in the tensile strength of warm-worked products is realizable by increasing tensile strength of steel before warm-working and work hardening by warm-working. As a strengthening method of warm-worked products by material strengthening, solid solution hardening is effective. Specifically, addition of Si is effective. As a strengthening method of warm-worked products by work hardening, low-temperature working is effective. Also the addition of elements such as Cr which inhibits the annihilation of dislocations can strengthen warm-worked products through increasing work hardening. Material strengthening by decreasing cementite spacing, etc. is less effective in strengthening of warm-worked products. This is by that plate-like cementites are changed to granular ones by warm-working.
  • Estimation of World Steel Demand and In-Use Stock for Ships

    pp. 135-142

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    DOI:10.2355/tetsutohagane.98.135

    Recovery of materials from end-of-life products will contribute to the reduction in consumption of natural resources and global warming. For many decades, ships have been a major share of steel use, and used high quality steel products, mainly plates and high tensile strength steel. So, the steels contained in end-of-life ships should be useful for secondary resources. Therefore, it is important to estimate the in-use stock and demand of steel for ships from past to future. In this study, we conducted material flow analysis of steel for ships in global scale to estimate the in-use steel stock and demand in the future for ships. As the result, world in-use steel stock of ships was estimated as 540 million ton in 2009, and predicted to reach 900 million ton in 2035, 1.7 times in 2009. It was expected that future steel demand for ships would increase up to 41 million ton in 2035.
  • Exploring the International Difference on Building Steel Intensity

    pp. 143-150

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    DOI:10.2355/tetsutohagane.98.143

    Steel is known as the most consumed metal in the world. Especially the use of steel in building and civil engineering sector accounts for the largest share in the total steel consumption. The flow and stock of steel has been intensively studied by material flow analysis (MFA) methodologies. The steel intensity for buildings largely depends on building structure, which is further decided by various factors, e.g. local economics, environment, frequency of earthquakes, culture, etc. However, these factors were seldom considered in previous MFA studies when estimating building steel stocks. In this paper, the worldwide difference in building structural composition was compared, and average building steel intensity was calculated. The authors examined the influence of GDP per capita, frequency of earthquakes, and average people killed per earthquake on the building structural composition, and the average building steel intensity. As the result, Asia-Pacific countries show relatively higher average building steel intensity than European countries, which is attributable to the seismic frequency. However, countries like China could have low average building steel intensity even with high seismic risk due to their low GDP per capita. These countries indicate high potential in growth of steel consumption in building sector in the future.

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