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

Tetsu-to-Hagané Vol. 103 (2017), No. 8

  • Fate of the Chlorine in Coal in the Heating Process

    pp. 443-450

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    DOI:10.2355/tetsutohagane.TETSU-2016-110

    Pyrolysis of 29 coals with carbon contents of 71-92 mass% on a dry, ash-free basis (daf) has been performed mainly in a temperature-programmed mode at 10ºC/min up to 800ºC with a flow-type fixed bed quartz reactor, and some factors controlling HCl formation have been examined. The rate profiles of HCl formation exhibit at least three distinct peaks at around 260-360, 470-510 and 580-630ºC, and the lowest temperature peak is present for 8 coals alone, whereas the middle and highest temperature peaks are common with almost all of the coals. The HCl profile is also affected by the size of coal particles and the height of coal particles in the fixed bed. Yields of HCl and char-Cl at 800ºC for 28 coals except an American bituminous coal are 44-95 and 4-54%, respectively, and tar-Cl is as low as ≤ 7% in all cases. The chlorine distribution is almost independent of the heating rate in the range of 2.5-400ºC/min and has no distinct relationship with carbon or chlorine content in coal, but HCl tends to increase with increasing amount of (Na + 2Ca) in coal with a corresponding decrease in char-Cl. When an Indonesian sub-bituminous coal is injected into an O2-blown entrained bed gasifier under pressure, there is an almost 1:1 relationship between carbon and nitrogen conversions, whereas the sulfur and chlorine are enriched in the remaining char, and the degree of the enrichment is higher with chlorine. The method of evaluating coal-Cl forms quantitatively using model chlorine compounds is proposed.
  • Visualization of 3 Dimensional Distributions of Non-Metallic Inclusions in Steels

    pp. 451-457

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    DOI:10.2355/tetsutohagane.TETSU-2017-018

    Non-metallic inclusions in steels are harmful for steel properties and measuring them is of large importance. Observation in a cross-section of steels has been used as a conventional way for inclusion measurement, however, it has lack of accuracy and spatial distribution of inclusions cannot be seen directly. In this study, 3-dimensional visualization was realized by using multi-sectioning way and composing 2D inclusion distribution images to 3D. A steel sample with aluminum oxide inclusions and a sample with titanium oxide inclusions were measured by the new way and the advantages of the way were discussed. Finally, the difference in inclusion distribution between both samples and its reason were considered.
  • Effect of Nozzle Geometry and Distance on Cooling Performance of Impinging Jets

    pp. 458-467

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    DOI:10.2355/tetsutohagane.TETSU-2017-016

    Gas jet cooling is widely used because the device is simple, it is possible to prevent oxidation and a uniform cooling ability can be obtained with thin steel sheets.Because the gas jet cooling ability is affected by the gas properties and nozzle geometry, quantitative evaluation of the influences of these factors is very important. A few non-dimensional empirical equations have been proposed for prediction of the gas jet cooling ability of geometrically arranged nozzles.In this research, the accuracy of Martin’s non-dimensional empirical equations was investigated by gas jet cooling experiments and fluid analyses with different nozzle geometries and distances from the cooled surface.Two nozzle geometries were examined, namely, a slit-like (linear) arrangement of round nozzles and a staggered arrangement of round nozzles.The difference between the experimental results and the results of predictions by Martin’s equations increased as the distance between the nozzle tips and the cooled surface decreased. It was suggested that the characteristic difference of the jet flow between the flow development region (potential core region) and the fully developed flow region influenced the cooling ability.The trend of divergence between the experimental and predicted cooling ability was clearly presented in this research. The results of this study make it possible to improve the accuracy of predictions when the distance between the nozzle tips and the cooled surface is set within the potential core region of the jet.
  • Sparse Modelling to Screen Microstructural Factors Dominantly Controlling a Stress-strain Curve of DP Steels

    pp. 468-474

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    DOI:10.2355/tetsutohagane.TETSU-2017-003

    Screening important microstructure factors dominantly controlling a stress-strain curve of a dual phase steel was studied by three kinds of sparse modelling approach; Sensitive analysis, data transformation & variable selection, and Bayesian inference. In addition, an effect of data noise on descriptor screening in sparse modelling was also investigated.
  • Voids Nucleation and Growth Examination during Tensile Deformation for IF Steel by Synchrotron X-ray Laminography and EBSD

    pp. 475-482

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    DOI:10.2355/tetsutohagane.TETSU-2017-011

    The mechanism behind the large elongation of Ti-added interstitial free (IF) steel has been investigated from the view point of voids’ nucleation, growth and coalescence in a local elongation region of tensile tests. Electron back scatter diffraction showed that in the case of IF steel, 50% of the voids nucleated at grain boundaries, 20% nucleated at Ti (C, N) on grain boundaries, 30% nucleated at Ti (C, N) in matrix. In the case of industrial pure iron, 70% of the voids nucleated at large angle grain boundaries while 30% nucleated at non-recrystallized grain boundaries. Synchrotron X-ray Laminograph observation showed that the voids in the IF steel grew, however, the coalescence was suppressed until a large plastic strain as compared with the pure industrial iron. Nano-indentation hardness (HIT) was measured when the tensile test stopped at a maximum load. This result showed that HIT at the grain boundaries of the industrial pure iron largely increased during tensile tests as compared with the IF steel. This finding was an indication that the industrial pure iron has heterogeneity of strain near grain boundaries previously in the region of uniform deformation. This finding also suggested that the large local elongation in the IF steel is caused by lowering heterogeneity of strain in the uniform deformation region followed by the suppression of voids’ growth and coalescence in the local elongation region.
  • Void Formation by Cementite and Local Misorientation Evaluation during Tensile Deformation in High Strength Steel Sheets

    pp. 483-490

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    DOI:10.2355/tetsutohagane.TETSU-2016-106

    Voids formation by cementite was investigated quantitatively in high strength steel sheets consisting of bainitic ferrite and cementite. Tensile tests were performed with rectangular specimen in longitudinal direction to rolling direction. After the tensile tests, the fractured specimens were cut along the width center. The cross sections near the fractured surface were observed by SEM. Voids and microstructure were observed in five thickness reduction areas with different strain level. As a result, number density of voids increased as strain increased. Not only the number of short voids observed in low strain but also the number of long voids increased as strain increased. Mainly, two types of voids were seen here. One was decohesion of interface between bainitic ferrite and cementite, and the other was cracking of cementite itself. Misorientation in the crystal grains was determined by KAM (Kernel Average Misorientation) using EBSD analysis. The obtained KAM values increased as strain increased, especially in the boundaries between bainitic ferrite and cementite. Therefore, it was revealed quantitatively that voids formed mainly through local strain increase.
  • Effect of Low Temperature Aging on Hall-Petch Coefficient in Ferritic Steels Containing a Small Amount of Carbon and Nitrogen

    pp. 491-497

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    DOI:10.2355/tetsutohagane.TETSU-2017-008

    Effect of aging treatment at 373 K on Hall-Petch coefficient (ky) was investigated in consideration of the change in friction stress associated with carbide/nitride precipitation in ferritic steels containing 60 ppm carbon or nitrogen (C60 and N60). Tensile tests revealed that the ky was monotonously increased with increasing aging time in both steels, and also, C60 exhibited a larger ky value than that of N60 under the same aging time. As a result of 3DAP analysis and theoretical calculation for grain boundary segregation of carbon and nitrogen, the ky corresponded to the amount of carbon and nitrogen existing at grain boundary. There was no difference in the effect on ky increment between both elements. The larger ky in C60 under the same aging condition was due to the larger amount of segregated carbon compared with nitrogen.

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