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

Tetsu-to-Hagané Vol. 95 (2009), No. 4

  • Local Structure of Crystalline and Amorphous Blast Furnace Slags by Solid-state NMR and MD Simulation

    pp. 321-330

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    DOI:10.2355/tetsutohagane.95.321

    Local environments of main constituent elements (Si, Al, O, Mg, and Ca) in slow-cooled (crystalline) and rapid-quenched (amorphous) blast furnace slags have been investigated using multi-nuclear solid-state NMR spectroscopy. The framework of the amorphous slag has a depolymerized, chain-like network (Q2) of SiO4 tetrahedra branched with AlO4 tetrahedra. AlO4 tetrahedra are more polymerized than SiO4 tetrahedra: Q3 and/or Q4. A 17O MQMAS spectrum demonstrates that oxygens occupy structurally inequivalent multiple sites due to a difference in their connectivities. 25Mg and 43Ca MQMAS spectra show that Mg21 and Ca21 ions also occur in multiple sites, and the average coordination number is estimated to about 6 and 7, respectively. Especially, Ca21 ions act as charge balancers of [AlO4]2 as well as network modifiers. The corresponding spectra of the crystalline slag prove the existence of melilite and a small amount of merwinite. A difference in chemical structure between the amorphous and crystalline slags is the coordination state of Mg21 and Ca21 ions rather than the framework of TO4 (T5Si or Al).
    Chemical structure of the amorphous slag has been also studied by means of MD simulation. Our calculation manifests that the structural properties at 300K agree well with the NMR results. At 1873K, the coordination number of the tetrahedral cations almost remains unchanged, while 5-fold Al species slightly increase. The Qn distributions of AlO4 tetrahedra are also modified. The small amount but significant incorporation of Al2O3 influences the network connectivities, which should affect macroscopic properties such as viscosity.
  • Analysis of Drainage Rate Variation of Molten Iron and Slag from Blast Furnace during Tapping

    pp. 331-339

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    DOI:10.2355/tetsutohagane.95.331

    Despite its importance in practical blast furnace (BF) operation, the dominant factors to control drainage rate or tapping time have not been well studied. In most cases, short tapping time has been attributed to rapid tap hole diameter enlargement. On the other hand, the experiential tendency about positive correlation between furnace hearth bottom temperature and drainage rate has been widely recognized.
    In order to examine the dominant factors to control the liquid drainage rate or tapping time at BF, a simulative calculation model is introduced, where the liquid drainage path consists of coke particles packed layer (coke filter) and tapping hole and the overall drainage rate is determined as one of smaller fluid rate in coke filter or tapping hole. For calculating the fluid rate in coke filter, a hypothesis that liquid iron and slag in coke filter is driven toward the tap hole entry point consuming the coke particles, whose extent depends on molten iron C saturation degree and FeO fraction in molten slag, was introduced.
    The calculation results present good matches with the observed tapping operation. This result can be explained by the two influences of low permeability zone formation or elimination at furnace hearth. Considering the two influences of low permeability zone formation, (1) to lower hearth bottom temperature and (2) to induce low C saturation of pig iron due to short traveling time in liquid pool to tap hole entry point, the simulation result conforms to the above mentioned experiential tendency.
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  • Plate-out Behaviors of O/W Emulsions for Cold Rolling in a Short Time Interval

    pp. 340-346

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    DOI:10.2355/tetsutohagane.95.340

    O/W emulsions are widely used in tandem cold rolling mills as coolants, in order to reduce friction forces and prevent heat scratches. The lubricating properties may be determined by various factors, and the amount of plated out oil on strip surface is one of the important ones, as well as dynamic concentration mechanics of emulsions at inlet of roll bite, on which much interest has been paid since 1970s. However, plate-out oil film formation has been recognized as a quite important factor in production mill operation, and the understandings of more details are necessary for higher speed and more efficient cold rolling mills. Therefore, the paper is concerned with the plate-out properties, especially the oil film formation in a quite short time. Because the plate-out oil formation is caused through phase transformation of O/W emulsion to oil film, the process may be time dependent, even if the time is quite limited in production high-speed rolling mills. In this paper, firstly a new method to evaluate the amount of plate-out oil is proposed, which makes it possible that the evaluation in quite a short time less than 0.1 s. Then, the time dependency of the oil film formation is clarified, and the amount of plated-out oil increases with time from emulsion supply to strip surface. Also, the influence of oil concentration, oil droplet size of O/W emulsions and other factors are examined by the method, which are compared with the results by conventional test methods.
  • Examination of Practical Performances of Water Soluble Lubricants in Temper Rolling

    pp. 347-354

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    DOI:10.2355/tetsutohagane.95.347

    Water soluble lubricants with practical performances are required in temper rolling process, such as promotion of surface roughness imprinting, prevention of micro-wear of work rolls, reduction of extraneous matters on a roll surface, rust proofing of a rolled steel sheet, without inhibition on performance of rust preventive oils used in next process, and selection of safety materials. However, the effects of water soluble lubricants on these practical performances have been reported in only a few studies. The reasons are as follows: (1) the effect of water soluble lubricants on each practical performance has been not clarified and (2) these practical performances can only be evaluated in detail after rolling with a long campaign.
    In this study, a water soluble lubricant with practical performances have been proposed and prepared. These practical performances of the new water soluble lubricant were compared to those of a commercially available soluble lubricant used in an actual temper rolling mill. The new water soluble lubricant is found to be superior to the commercial water soluble lubricant in almost every performances including roll micro-wear, surface imprinting, reduction of extraneous matters, without inhibition on performance of rust preventive oils, and safety. The new water soluble lubricant shows the rust proofing equaling to the commercial water soluble lubricant. Therefore, the new water soluble lubricant is considered to be applicable for actual temper rolling mills.
  • Microstructures and Concentration Profiles Formed between Solid Fe and Liquid Zn–0.2wt%Al Alloy at 723K

    pp. 355-360

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    DOI:10.2355/tetsutohagane.95.355

    Microstructure and reactive diffusion between solid Fe and liquid Zn–0.2wt%Al was experimentally examined using Fe/Zn–Al diffusion couples prepared by the immersion technique, where a pure iron sheet was immersed in a molten Zn–Al bath at 723K (450°C) for various times up to t52.4 ks. The microstructures on the cross section in the Fe/Zn–Al diffusion couples were observed by scanning electron microscopy, and the chemical composition of each phase was determined by electron probe microanalysis. While in the initial stage the formation reaction of the Fe–Zn layer is suppressed, the outburst reaction drastically occurs at around 180 s and the Fe–Zn layer grows in proportion to immersion time. It was found that in the early stage before the outburst the interface concentration of Fe in the liquid-Zn (L) phase at the Solid-Fe/L interface is about 3 wt% being extremely higher than the equilibrium value and that the difference from the equilibrium condition drastically decreases by the formation of the Fe–Zn layer. Furthermore, the concentration change of Fe in the Zn–Al melt induces an up-hill diffusion of Al, and some amount of Al is always supplied from the melt to the Fe/L interface. These results seem to be important to understand the formation mechanism of the Fe–Al inhibition layer.
  • Effect of Local Multi-axial Stress on Creep Crack Growth Behavior in the Heat Affected Zone

    pp. 361-368

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    DOI:10.2355/tetsutohagane.95.361

    Under the multi-axial stress field, creep crack growth is considered to occur in brittle manner. From the view point of practical use, it is important to conduct the characterizations of the creep crack growth rate and its life under the multi-axial stress field to predict the life of creep crack growth. In the present study, for the welded joint of the W-added 9Cr ferritic heat-resistant steel, ASME Code Case 2179/ASTM A335 P92, creep crack growth tests and 3-dimensional elastic-plastic creep finite element analyses were conducted to clarify the effect of stress multi-axiality on creep crack growth. As a result, the creep ductility of welded joint was found to decrease and shift to the creep brittle region as compared with that of base metal due to the large value of stress tri-axial factor TF.
  • Influence of Shot Peening on Surface Hot Shortness of Copper Containing Steel

    pp. 369-377

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    DOI:10.2355/tetsutohagane.95.369

    The recycling of scrap steels is a global issue due to the environmental problem. Tramp elements such as Cu and Sn that they can contain cause surface cracking of steels during hot rolling process (i.e., the liquid embrittlement by Cu). This paper describes the influence of shot peening on the surface hot shortness of x% Cu (x50, 0.4 and 0.6) containing low carbon–Nb–V steel. These materials were shot peened by Al2O3 at room temperature and they were subjected to 1100°C oxidation in air or in water vapor contained atmosphere followed by tensile strain or compression strain. Surface hot shortness was assessed by measuring the number and depth of surface cracks occurring in the specimens. It was found that shot peening largely changed the oxidized scale structure such as Fe2O3/Fe3O4 and Fe3O4/FeO interfaces, the volume fraction of voids in the scale, and the distribution of Cu enriched alloy at the interface of scale/steel, thereby suppressing the hot shortness of Cu steels.
    The authors discussed this mechanism by macroscopically homogenous and microscopically heterogeneous oxidation due to the introduction of defects such as dislocations and lattice distortions into surface layer of Cu steels by shot peening. It was concluded that shot peening is high potentialities for suppressing the hot shortness of Cu containing steel as a new method other than using expensive nickel.
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    3. Effect of Oxygen Concentration on Surface Hot Shortness of Steel Induced by Copper ISIJ International Vol.55(2015), No.5
  • Effect of Stress Ratio on Fatigue Properties of High-strength Steels

    pp. 378-383

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    DOI:10.2355/tetsutohagane.95.378

    Fatigue tests were conducted for three heats of 1800 MPa-class spring steels under various R ratios. For comparison, similar fatigue tests were conducted also for conventional steels whose tensile strength was lower than 1200 MPa. The spring steels showed fish-eye fracture, eliminating conventional fatigue limits, and the fish-eye fracture origins were oxide, TiN and matrix itself, respectively. On the other hand, the conventional steels never showed fish-eye fracture and clearly showed fatigue limits. Fatigue strength of these steels was monotonously decreased according to increase of the R ratio, when the fatigue strength was evaluated with stress amplitude. However, the degradation of the fatigue strength was smaller than that expected from a modified-Goodman line, and the best fit line was obtained by drawing σW(R=−1)–σT line. When the stress ratio effect was evaluated with a function of (12R)γ, the estimated γ value was 0.5. In these results, difference was negligible between the spring and conventional steels. This meant that the stress ratio effect could be evaluated in conventional manners even in case of high-strength steel showing fish-eye fracture, regardless of the fish-eye fracture origin types.
  • Discussion on the Vortex Depth in Mechanical Centric Agitation

    pp. 384-386

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    DOI:10.2355/tetsutohagane.95.384

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