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

Tetsu-to-Hagané Advance Publication

  • Crystal Plasticity Analysis on Ductility of Ferrite/Cementite Multilayers: Effect of Dislocation Absorption Ability of the Hetero Interface

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    DOI:10.2355/tetsutohagane.TETSU-2018-082

    Strain hardening behavior of ferrite layers in the microstructure of drawn pearlite wire is studied theoretically and numerically. It is shown that stress field associated to dislocations could diminish quickly if the dislocations enter the phase or grain boundaries and decompose into smaller segments to distribute along the boundary. Some atomistic simulations of single-phase media validate this phenomenon; dislocations show to pass, decompose or accumulate on tilt-type grain boundaries depending on their atomistic configuration. Mechanical responses of nine-layered pearlite models subjected to tensile load are analyzed by a strain gradient crystal plasticity finite element code, where possible passage or absorption of dislocations is expressed in the model of dislocation mean free path. The critical resolved shear stress for slip systems consists of the lattice friction, the Taylor and Orowan terms and the strain hardening is given by the Taylor one. The density evolution of accumulated dislocations is evaluated by the model of Kocks and Mecking where the dislocation mean free path plays a major role. Results show that the smaller the dislocation absorption ability of the phase boundary and thinner the layer thickness, larger the strain hardening becomes. Slip localization in cementite layers is shown to be suppressed when the strain hardening of ferrite layers is higher, and this trend is consistent with results obtained in previous studies by molecular dynamics simulation and classical elasto-plasticity analyses. Scale sensitive phenomena taking place at phase boundaries in layered structure are briefly discussed in views of atomistic process and continuum mechanics.
  • Structural and Mechanical Characterizations of Top Dross in a Molten Zinc Bath

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    DOI:10.2355/tetsutohagane.TETSU-2018-127

    In a molten zinc bath in a continuous galvanizing line (CGL), top dross particles crystallize as Fe-Al-Zn intermetallic compounds. These particles easily adhere to the steel sheets causing surface defects. Therefore, controlling the top dross particles is a key issue. The present study focused on the structural and mechanical characterizations of top dross particles using an electron probe micro analyzer, X-ray diffraction, electron back scattering diffraction, Vickers hardness measurement and nano-indentation measurement. The following results were obtained: (1) The crystal structure of top dross particles Fe2Al5Znx having Fe: 37~38 wt%, Al: 44~45 wt% and Zn: 18~19 wt% belongs to the orthorhombic system with a lattice constant of a=7.61 Å, b=6.48 Å and c=4.23 Å. The a axis of Fe2Al5Znx becomes shorter, while the b and c axes become longer compared to those of binary Fe2Al5. (2) The top dross particles with the faceted interface were postulated to coarsen by the mechanism of the anisotropic interface energy between the top dross particles and molten Zn as a driving force rather than by the aggregation mechanism. (3) The hardness and the elastic modulus of the top dross particles are the lowest in the [001] direction like Fe2Al5, and are lower than those of Fe2Al5. (4) The fracture toughness of top dross particles is approximately 1.1 MPa·m1/2, which is slightly lower than that of Fe2Al5.
  • Multi-step Simulation of Vacuum-carburizing Reactor based on Kinetics Approach

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    DOI:10.2355/tetsutohagane.TETSU-2018-108

    A novel and efficient simulation technique for the purpose of optimization of vacuum-carburizing process was proposed. This method consists of three steps: calculation of gas convection and diffusion, calculation of only gas diffusion, and calculation of carbon diffusion in steel. The first step provides the gas convection velocity that is employed in the second step. Adsorption rate of carbon on the steel surface is obtained in the second step, and carbon concentration in the steel is calculated in the third step based on the adsorption rate of carbon. Experiments were conducted to verify the proposed method in both laboratory- and industrial-scale reactors. Comparison of the computational predictions to the experimental data revealed that the proposed technique enabled accurate prediction of the adsorption rate of carbon on the steel surface at various temperature conditions, the amount of carburized carbon at each operating time, and the profile of carbon concentration in the steel; in other words, the carburized depth. In addition, the calculation of the industrial-scale reactor, whose simulation model consisted of approximately seven million computational meshes, was completed within about two days. Therefore, the proposed simulation technique could be used to control and optimize the process in industrial vacuum-carburizing reactors.
  • Effect of Boron Addition for on Time Temperature Transformation Behavior in Si Added High Carbon Steels

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    DOI:10.2355/tetsutohagane.TETSU-2018-055

    In high carbon steel, TTT nose temperature rises and upper baninte becomes easy to be formed with quantity of Si addition. Generation of upper bainite is reduced by boron addition. In this study, the influence of boron addition on isothermal transformation behavior in Si-added high carbon steel was clarified. By boron addition, lamellar spacing and growth rate of pearlite doesn’t change, but the nucleation of pealite is reduced. But nucleation of pearlite is promoted when Fe23(C,B)6 precipitates. In the Si-added high carbon steel, upper bainite is often formed with the generated ferrite on prior austenite grain boundary. It is inferred that boron reduces ferrite generation in grain boundary which causes upper bainite formation. It is confirmed that effective existence state of boron is grain boundary segregation.
  • Development of Microstructurally Small Fatigue Crack Initiation and Growth Evaluation Method Using Automatic In-situ Observation System with Digital Image Correlation Technique

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    DOI:10.2355/tetsutohagane.TETSU-2018-096

    We constructed an automatic in situ fatigue observation system to monitor small fatigue crack behavior at the microstructural level. Applying a digital image correlation (DIC) technique in combination enabled us to continuously and automatically track and record microscopic deformation behavior. To verify the effectiveness of this system, we applied it to small fatigue crack evaluation in heat-treated low-carbon steel. The results demonstrated the feasibility, using our developed system, of automatically tracking and recording microstructurally small fatigue crack initiation and early growth behavior. By utilizing DIC analysis, we also succeeded in visualizing microscopic deformations such as inhomogeneous strain concentration by microstructures causing fatigue cracks and small fatigue crack opening-closing behavior. Although early stage fatigue crack growth rate accelerated compared to long crack data, it was consistent with long crack data by using ΔKeff calculated from crack open stress measured by DIC.
  • Development of Niobium Bearing High Carbon Steel Sheet for Knitting Needles

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    DOI:10.2355/tetsutohagane.TETSU-2018-097

    Effect of Nb addition less than 0.05 mass% on the quench and tempering behavior of spheroidized eutectoid steel, which has been usually applied to knitting needles, was investigated. The results obtained are as follows. 1) Hardenability with brief heating was markedly improved by 0.01 mass% Nb addition. 2) Both quenching elongation and its standard deviation decreased with 0.01 mass% Nb addition compared to those of Nb free steel. 3) While the effect of Nb addition on the hardness change during low temperature tempering was hardly observed, not only the impact toughness but also the fatigue durability were improved with 0.01 mass% Nb addition. 4) APT (Atom Probe Tomography) analyses indicated that the precipitation of carbon in solution proceeded directly to the ε and/or θ carbides with carbon contents of higher than 25 at% by Nb addition without going through a clustering process up to 10~15at% during low temperature tempering. 5) In spite of the same content of P, the average bulk concentration of P in the martensite phase markedly increased with the addition of Nb up to 0.05 mass%. 6) Regarding the optimum content of 0.01 mass% Nb on the various mechanical properties under the low temperature tempering of martensite, it is considered that they are dominated by the sum of the positive effect for promoting carbide precipitation during low temperature tempering with Nb addition and the negative effect for deteriorating the toughness with increasing bulk concenteration of P in the martensitic phase with addition of Nb higher than 0.02 mass%.
  • Mechanical Investigation on Interface Failure Mechanisms of Dissimilar Welded Joints

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    DOI:10.2355/tetsutohagane.TETSU-2018-052

    2 types of dissimilar welded joints (DWJ), Mod.9Cr-1Mo steel / Alloy 600 / SUS304, which were differential heat input during welding to the ferrite steels were manufactured in this study. Welding methods for Mod.9Cr-Mo steel were used Plasma Arc Welding (PAW) and GTAW, respectively. Constitutions of the heat affected zone (HAZ) formed in Mod.9Cr-1Mo steel were different in PAW and GTAW. The coarse grain HAZ (CGHAZ) was formed in Mod.9Cr-1Mo steel adjacent to Alloy 600 in the dissimilar welded joint by PAW (PAW_DWJ). In contrast, the fine grain HAZ (FGHAZ) was formed in Mod.9Cr-1Mo steel adjacent to Alloy 600 in the dissimilar welded joint by GTAW (GTAW_DWJ). Specimens were sampled from Mod.9Cr-1Mo steel / Alloy 600 part. Creep tests were conducted at 550°C. In creep tests, a GTAW_DWJ failed at the interface, the PAW_DWJs failed at Mod.9Cr-1Mo steel part i.e. not at the interface. Therefore, the Speckle Image Correlation Analysis (SPICA) and the Finite Element Method (FEM) in specimens were carried out to analyze the deformation behavior of the HAZ to focus on mechanical factors of the interface failure mechanisms. SPICA revealed that the concentration of strain in the PAW_DWJ was issued the width of CGHAZ away from interface. The analysis combined with FEM results suggests that slow creep strain rate of CGHAZ formed adjacent to Alloy 600, the difference in creep strain rate between Mod.9Cr-1Mo steel and Alloy 600 was able to be mitigated. As a result, a noticeable shear stress causing interface failure wasn’t issued in the PAW_DWJ.
  • Development of Shape Meter Employing LED Dot Pattern Projection Method for Hot Strip Finishing Mill

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    DOI:10.2355/tetsutohagane.TETSU-2018-099

    In recent years, in order to improve the fuel efficiency of automobiles by reducing their weight with maintaining strength, the thinner thickness and higher strength steel sheets tends to be used as their construction materials. For stable and accurate production of these sheets, it is very important for these to be flattened at hot strip rolling process. Therefore, to realize accurate AFC (Automatic Flatness Control), a new shape meter which employed LED dot pattern projection method was developed. This is consist of LED dot pattern projector which can project the staggered periodic dot pattern, formed of 1200 power LED chips, on the rolled strip and area camera which captures the image of projected pattern. Then, instantaneous strip flatness is measured by analyzing the pattern pitch correlative with inclination angle. The shape meter was installed at the hot strip finishing mill exit and evaluated its measurement accuracy and stability. As a result, its inclination angle measurement error was within 0.45 degrees (two sigma) by comparing with the set angle of standard target and the measured flatness of rolling strip was consistent with the visually observed one. Its measurement success rate per entire coil was exceeded above 98.5%. These results indicated that the developed shape meter would be able to apply to the AFC. In addition, applying the measured flatness to the AFC of the work roll bender and leveling, it was confirmed that the strip flatness was improved in a short time.
  • Development of Biaxial Tensile Test System for in-situ Scanning Electron Microscope and Electron Backscatter Diffraction Analysis

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    DOI:10.2355/tetsutohagane.TETSU-2018-122

    For the further improvement of the press formability of steel sheets, it is important to clarify the relationship between macro mechanical properties and microstructure under multi-axial deformation state. The objective of this work is to develop the experimental system of in-situ observation and analysis for biaxial tensile deformation using electron back scatter diffraction patterns (EBSD) with scanning electron microscope (SEM). The appropriate shape of cruciform specimen for the system was examined first by using finite element analysis, and the biaxial tensile test system in vacuum SEM chamber was developed. In-situ observation of microstructure during equibiaxial tensile deformation was then conducted using the developed system and the proposed cruciform specimen. The material used in this study was an interstitial-free steel. It was validated by the comparison with the results obtained by the Marciniak type macro test that the developed system realized equibiaxial tensile deformation. Finally, some information obtained from SEM and EBSD analysis was illustrated. It was found for example that the grains with {001} plane orientations deformed easily and might cause the surface roughness.
  • Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP added PAO Lubrication in Nanostructured Steels

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    DOI:10.2355/tetsutohagane.TETSU-2018-043

    The effect of lattice defects on the tribological behavior for high friction coefficient under tricresyl phosphate (TCP) added poly-α-olefin (PAO) lubrication was investigated in the nanostructured steels produced by heavy plastic deformation processes. In the surface-nanostructured SUJ2 bearing steel, the tribological behavior with high friction coefficient was observed in the ball-on-disk tests in comparison with the non-deformed steel. In addition, the similar phenomenon was observed in the ultra-low carbon (ULC) steel with high-density of lattice defects (grain boundary, dislocation and so on). By increasing the density of lattice defects, higher friction coefficient was shown. The reason of the tribological behavior with high friction coefficient seems that the compound film of Fe-O-P system formed in the ball-on-disk test was worn.
  • Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

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    DOI:10.2355/tetsutohagane.TETSU-2018-077

    Our strategy to enhance fracture properties of ultra-high-strength low-alloy steel with a yield strength of 1.4 GPa or over is to arrest the propagation of brittle crack in a hierarchical, anisotropic and ultrafine grain structure designed to be fail-safe, in addition to suppressing the crack initiation. The present article reviews strength, ductility, toughness and delayed fracture resistance of ultra-high-strength low-alloy steel with an ultrafine elongated grain structure that was processed by deformation of a tempered martensitic structure at an elevated temperature (warm tempforming). The evolution of heterogenous microstructure during warm tempforming using multi-pass caliber rolling and the microstructural factors controlling the strength and the fracture properties of the warm tempformed steels are discussed. Furthermore, we introduce the application of the warm tempformed steel with an ultrafine elongated grain structure to ultra-high-strength bolt.
  • 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.
  • 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.

Article Access Ranking

15 Nov. (Last 30 Days)

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  2. Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt Tetsu-to-Hagané Advance Publication
  3. Off-line Model of Blast Furnace Liquid Levels ISIJ International Advance Publication
  4. Fusion Zone Microstructural Evolution of Al-10% Si Coated Hot Stamping Steel during Laser Welding ISIJ International Advance Publication
  5. Mathematical Modelling of the Effects of Transient Phenomena on Steel Cleanness during Tundish Transfer Practices ISIJ International Advance Publication
  6. Phase Transformation of Cohesive Zone in a Water-quenched Blast Furnace ISIJ International Vol.58(2018), No.10
  7. Preparation of High-Carbon Metallic Briquette for Blast Furnace Application ISIJ International Advance Publication
  8. Phase Transformation Behavior of Oxide Scale on Plain Carbon Steel Containing 0.4 wt.% Cr during Continuous Cooling ISIJ International Advance Publication
  9. Nanocluster Control for Achieving High Strength Aluminum Alloys MATERIALS TRANSACTIONS Vol.59(2018), No.6
  10. Effect of Annealing Time on Oxides Phases and Morphology along Oxidized Depth of Fe-3%Si Steel during Decarburization ISIJ International Advance Publication

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