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

Tetsu-to-Hagané Advance Publication

  • Reaction Behavior of Thermal Decomposition of Limestone in the Presence of Carbon –Reactivity Evaluation by Deep Learning–

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    DOI:10.2355/tetsutohagane.TETSU-2018-040

    This paper discussed reaction on thermal decomposition of limestone and Boudouard reaction.Thermogravimetric analysis of mixed powder samples of limestone and carbonaceous material was carried out. The ratio of the sequential reaction, αc was 0.65 when limestone powder with large particle size and graphite powder with small particle size were used. It was found that the reactivity varies depending on the states of dispersion and mutual coating of the powder particles. Deep learning by recurrent neural network (RNN) and convolutional neural network (CNN) was applied to calibrate weight loss curve of TG analysis and predict reactivity of samples. The TG curve corrected by RNN was almost equivalent to that processed manually. CNN required more learning to evaluate the reactivity of the sample more accurately in the present conditions. We presented that the constructed models are extremely powerful tool for evaluation of metallurgical reactions.
  • Fatigue Crack Growth under Non-proportional Mixed Mode I/III Loading in Rail and Wheel Steel

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    DOI:10.2355/tetsutohagane.TETSU-2018-059

    Fatigue tests were performed to obtain co-planar and branch crack growth rates on rail and wheel steel under non-proportional mixed mode I/III cycles. In the experiments, sequential and overlapping mode I and mode III cycles that simulated the load experienced by the rolling contact fatigue cracks were applied to the crack in cylindrical specimens made of rail and wheel steel. Experiments showed that a long co-planar crack could be produced under certain loading conditions. Based on the fracture surface observations by SEM and the results of FEA, the long co-planar crack growth is thought to be driven mainly by mode III loading and the role of mode I is an assistant, keeping the crack face opened. It was observed that the cracks were apt to branch when the strength of the material increased. It was also observed that the crack branched when the degree of overlap between the mode I and mode III cycles increased. We proposed the equivalent stress intensity factor range for branch crack that can consider the crack face contact and successfully regressed the crack growth rate data. Comparing the fracture surfaces and the co-planar crack growth rates data under non-proportional mixed mode I/III loading with that under I/II loading, it is found that the mechanism of shear mode crack growth is essentially the same regardless of whether the main driving force is in-plane shear or out-of-plane shear.
  • Effect of Cold Deformation Prior to Induction Heating Austenitization on Dissolution Speed of Carbide in SUJ2 Steel

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    DOI:10.2355/tetsutohagane.TETSU-2018-039

    The effect of prior cold deformation on the dissolution speed of carbide in SUJ2 bearing steel subjected to induction heating austenitization at 920°C was examined. Microscopic observations using scanning electron microscopy and transmission electron microscopy, in addition to crystallinity measurements using powder X-ray diffraction, found no trace of the cold deformation effect in the carbide and few crystal defects in the spheroidal carbide particles of an as-received specimen. However, it is important to note that the cold deformation resulted in a refinement of austenite grains during austenitization, which accelerated the dissolution of chromium from the carbide compared to an unprocessed specimen. This led to enhancement of the resultant carbon diffusion in a matrix.The volume fraction of carbide present at grain boundaries was estimated assuming a simple geometrical model. The relationship between the holding time and the volume fraction of undissolved carbide was derived based on a bulk diffusion model of chromium into an austenite matrix. Experimental results on the dissolution speed of carbide were qualitatively explained by considering the combination of grain boundary diffusion and bulk diffusion. The austenitization behavior of SUJ2 steel is remarkably influenced by the microstructure, in particular for short austenitization times.
  • Coupled FEM Simulation of Induction Heating Process in the Austenitization of a SUJ2 Steel Ring

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    DOI:10.2355/tetsutohagane.TETSU-2018-065

    The applicability of the finite element method coupled with electromagnetic field analysis and heat conduction analysis to optimization of induction heating of a bearing raceway was assessed. In order to obtain temperature uniformity in a heated raceway, precise design of the coil arrangement and heating schedule are required. It is important to know how the internal temperature changes with time for the development stage.The one-dimensional skin current model predicts that the temperature difference between the outer and inner surfaces decreases and that the temperature becomes uniform as the heating region moves inward when the outer surface temperature nears the Curie point. This phenomenon was reproduced in simulations and experiments for a ring sample, but it depended on the balance between the thickness of the ring and the penetration depth of the electromagnetic field. It is necessary to set an appropriate rate of temperature increase and frequency for the power source according to the thickness of ring.High accuracy analysis was possible by using temperature-dependent B-H characteristics when a heated ring was in the ferromagnetic state. However, in the paramagnetic state, the agreement between simulation and experiment became worse. This may be due to the high rate of temperature increase used in this study, which suggests that the shift in the transformation point to high temperature must be taken into account.
  • Behavior of Crystallization on a Continuous Solidification Process of Blast Furnace Slag

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    DOI:10.2355/tetsutohagane.TETSU-2018-032

    A continuous blast furnace slag solidification process was developed to promote the use of air-cooled slag coarse aggregate for concrete. In this process, molten slag can be solidified in only 120 seconds, and the thickness of the slag is about 25 mm. After crushing the slag, the water absorption ratio is much lower than that achieved in the past because gas generation is suppressed. With this apparatus, most of the slag is crystalline, but part of the slag has a glassy surface. Therefore, EPMA and XRD were used to study the glass transition phenomenon. It found that the thickness of the glass layer is about 2 mm. To discuss the glass transition and crystallization phenomena, the thermal history was simulated by heat transfer analysis. The results clarified the fact that all the slag on the mold has a glassy surface layer of about 2 mm, and good agreement between the calculation and experimental data concerning the layer was obtained. It was also shown that most of the slag crystallizes in the slag pit because the temperature inside the piled slags rises to more than 1173 K. The measured slag temperature and calculated temperature were also in good agreement.
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  • Observation of Chemical State for Interstitial Solid Solution of Carbon in Low-carbon Steel by Soft X-ray Absorption Spectroscopy

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    DOI:10.2355/tetsutohagane.TETSU-2018-050

    Observation of chemical state of solid-solution carbon in a low-carbon steel was tried by C-K near-edge x-ray absorption fine structure spectra measurement. In addition, the wavelength dependence of the photoelectron spectrum on the surface of the bulk steel was evaluated, and the contamination and oxidation layer of 3 nm in thickness on the surface of the steel was found. As a result, it was possible to observe the chemical state change of carbon existing in the bulk iron located deeper than the oxidation and contamination layer, by evaluating the difference spectra between the sample and the reference. Furthermore, by evaluating the shape change of the difference spectra depending on the heat treatment time, this study suggested that the chemical state of carbon in bulk iron changes with heat treatment.
  • Lattice Strain and Strength Evaluation on V Microalloyed Pearlite Steel

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    DOI:10.2355/tetsutohagane.TETSU-2018-041

    Strengthening effect by microalloyed vanadium (V) on eutectoid pearlite steel has been investigated from the perspective of nano-precipitation and lattice strain. 0.2% proof stress of specimens, isothermally transformed at 873 K, increases around 160-170 MPa with 0.1% V addition. However, interphase precipitation of vanadium carbide (VC), regarded as the principal strengthening factor, has not been detected by transmission electron microscopy or 3D atom probe microscopy (3D-AP). On the other hand, lattice strain in lamellar ferrite, analyzed by broadening of X-ray diffraction peak, has clear correlation with proof stress. The lattice strain data of 0.1% V added pearlite specimens are plotted on the same correlation line as of V free ones. In addition, elemental map by 3D-AP shows that vanadium atoms concentrate in lamellar cementite rather than ferrite, which could change cementite lattice parameters and gain ferrite/cementite misfit causing lattice strain increment. These results reveal that microalloyed V influences not only precipitation of VC in lamellar ferrite, but also the lattice strain increment in pearlite lamellar. As far as pearlite steels containing at most 0.1% V, lattice strain is considered to be the major factor of their yield behaviors. Furthermore, 0.1% V addition has not enhanced work-hardening behavior as notably as estimated by Ashby’s work-hardening theory of dispersion-hardened crystals. Therefore, VC precipitation should not necessary for V strengthening effect on pearlite steel.
  • Recovery of Neodymium from Neodymium Magnet Using Bismuth

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    DOI:10.2355/tetsutohagane.TETSU-2018-037

    Experiments were conducted to extract neodymium in bismuth by melting Fe-Nd-B magnets and bismuth together in a graphite crucible at 1200°C. Molten iron and bismuth separated into two phases, and neodymium in the magnet dissolved in the bismuth phase. Neodymium dissolved in bismuth was considered to form BiNd as a result of XRD. The neodymium concentration in iron phase after the dissolution treatment was 0.05 at.% or less,and the recovery rate was 99% and more. Compared to other metals(Mg, Ag, Cu) that separate into two phases with respect to molten iron, bismuth can be said to be a metal extraction material with a low melting point, safety and low energy cost.
  • Simulation of Snaking and Buckling in Hot Sheet Rolling

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    DOI:10.2355/tetsutohagane.TETSU-2018-023

    In hot sheet rolling, the sheet end often snakes, contacts the side guide, buckles, and goes into the roll gap, while the overlapped sheet end is squeezed. Although many simulations on sheet snaking are reported, very few researches have been performed to simulate both the sheet snaking and sheet buckling. In this study, we proposed a combined method to simultaneously simulate the sheet snaking through the rigid-plastic FEM and to analyze the sheet buckling by the elementary theory of buckling. The in-plane lateral load and the in-plane bending moment were assumed at the surface of the region for the simulation by the rigid-plastic FEM. The amount of snaking at the sheet end simulated by the rigid-plastic FEM agreed with that calculated from the analysis by the elementary theory. Finally, we clarified the effects of rolling conditions on the occurrence of squeezing, such as the difference in the sheet thickness in the roll axis direction, the difference in the roll gap in the roll axis direction, and the amount of the off-center.
  • Effect of Crystal Structure of Surface Compound Layer on Fatigue Strength of Nitrided SCM 435 Steel

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    DOI:10.2355/tetsutohagane.TETSU-2018-011

    Effect of crystal structure of surface compound layer on the fatigue strength of nitrided SCM 435 steel was investigated. Specimens in which the crystal structure of the surface compound layer was controlled to γ’-Fe4N phase or ε-Fe2-3N phase were prepared by gas nitriding treatment capable of changing nitriding potential (KN). Axial fatigue test were conducted to the specimens. Even in each test specimen which has different crystal structure of the compound layer, distribution of residual stress and hardness in the nitrogen diffusion layer exhibited almost same values. It is revealed that fatigue strength significantly depends on crystal structure of surface compound layer. Specimens with γ’-Fe4N phase dominant shows substantially high fatigue strength comparing to specimens with ε-Fe2-3N phase dominant. In the fatigue test under stress ratio R=0, the specimen from which the surface compound layer was removed showed the highest strength. The fatigue strength is considered to be governed by the fracture strength of each compound layer. Namely, in the specimen with ε-Fe2-3N phase dominant, fatigue cracks are induced by fracture of brittle ε-Fe2-3N phase layer and progress into nitrogen diffusion layer due to stress intensity factor (ΔK) at crack tip exceeds the threshold of stress intensity factor range (ΔKth) in the matrix. On the other hand, in the case of γ’-Fe4N phase dominant, γ’-Fe4N phase with high toughness showed high fatigue strength due to suppress the crack initiation up to a higher stress level.

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