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

Tetsu-to-Hagané Vol. 94 (2008), No. 1

  • In-situ Observation of Weld Solidification and Transformation Using Synchrotron Radiation

    pp. 1-5

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    DOI:10.2355/tetsutohagane.94.1

    Time-resolved X-ray diffraction system was studied to characterize the unidirectional solidification and the phase transformation during welding. Experimental conditions including wavelength of X-ray, scattering angle, incident angle and time-resolution for analyzing the solidification process in welding were made clear. Furthermore, heating and solidification processes for weld metal of 13Cr–9Ni steel in TIG welding were in-situ analyzed by using the system. The primary phase was identified as delta-phase during solidification with halo pattern for liquid phase, followed by the peritectic reaction with a spot-like diffraction pattern for delta-phase and austenite phase.
  • Microbiologically Influenced Corrosion Behavior in Stainless Steels for Public Sewage Treatment Plants

    pp. 6-12

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    DOI:10.2355/tetsutohagane.94.6

    A study was performed on the cases of corrosion regarded as microbiologically influenced corrosion (MIC), for stainless steel centrifuge, which had been used in the processes of sludge concentration and dehydration in public sewage treatment plants. Evaluation was made on chemical concentrations of the steels and macroscopic as well as microscopic features on the corrosion status. Most of the cases relate to cast stainless steel with two-phase microstructure similar to that of weld metal. A number of studies have been reported so far on the cases where MIC occurs on stainless steel in seawater and fresh water, but there have been very few reports on the cases of damage in sewage treatment plant. Further, almost no study described the corrosion of a material such as duplex stainless steel with highly corrosive property. It is known that MIC is very likely to occur on weld metal. As the causes of the corrosion, special attention is now focused on influence of oxidation and reduction in the environment and relation between two-phase microstructure and MIC such as galvanic effect of austenite phase and ferrite phase in stainless steel weld metal microstructure.
  • Crack Initiation Behavior from Internal Defect in High Carbon-chromium Bearing Steel under Rolling Contact Fatigue

    pp. 13-20

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    DOI:10.2355/tetsutohagane.94.13

    It is important to clarify the effects of nonmetallic inclusions on rolling contact fatigue life to extend or to predict the life of the rolling bearings. The observation of initial cracks from internal defects is desirable from this point of view. In this study, high carbon-chromium bearing steel, SUJ2, with a number of artificial pores as internal defects was prepared. Initial cracks around pores under rolling contact were observed and the stress was CAE analyzed with the following results:
    - The exposure of the initial crack surface by forced breaking and the subsequent fracture observation in this study were effective to identify the mode of the initial crack generation.
    - The tensile stress around the pores initiated mode-I crack, and the pore with cracks is subjected to crack propagation process by internal stress under rolling contact fatigue.
    - Rolling contact fatigue life is not simply dominated by the size of initial defects in steels. As observed in this study, the sum of initial defect size and rim crack size may control the fatigue life. This suggests that the inclusion types and the interfacial adhesiveness between inclusions and matrix may influence rolling contact fatigue.
  • Simulation of TiC Precipitation in Ti-added Low Carbon Steel

    pp. 21-29

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    DOI:10.2355/tetsutohagane.94.21

    Precipitation of TiC from austenite or ferrite in Ti-added low carbon steels is simulated using an N-model. The time-dependent nucleation rate is calculated from classical nucleation theory, assuming that nucleation occurs preferentially along dislocations and the critical nucleus is a parallelpiped with {100}TiC facets. The growth rate is calculated using the mean field approximation assuming that the transport of solute (Ti) along dislocations accelerates the growth. Results show that at the first stage precipitation proceeds rapidly almost to the final volume fraction. Then, the precipitation enters the second stage in which neither the particle density nor the size vary appreciably, which continues quite a long time until the particle density begins to decrease, i.e. coarsening begins (the third stage). From comparison with isothermal holding experiments conducted at 1000°C for austenite and 580°C for ferrite, the precipitate/matrix interfacial energy which includes the interaction of a nucleus with the strain field of dislocation is evaluated to be 0.20–0.25 J/m2 for austenite, which are comparable with the values reported by other authors, whereas it is 0.35–0.50 J/m2 for the side facet of a TiC particle in ferrite.
  • Fabrication and Mechanical Properties of Lotus-type Porous Carbon Steel by Unidirectional Solidification in Nitrogen Atmosphere

    pp. 30-34

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    DOI:10.2355/tetsutohagane.94.30

    Lotus-type porous carbon steel (AISI1018) whose long cylindrical pores are aligned in one direction was fabricated by unidirectional solidification in pressurized nitrogen gas. The ingots with the porosity from 10 to 30% were fabricated under the nitrogen gas pressure of 2.5 MPa at various transference velocities from 40 to 160 μms−1. Tensile strength was measured for Lotus-type porous carbon steel. Elongation was improved due to normalizing at 1200K. The yield strength does not change even in lotus steel less than 20% in porosity.
    This superior property is attributed to nitrogen solid solution hardening and pore existence.

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