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

Tetsu-to-Hagané Advance Publication

  • Fatigue Strength Improvement by Replacing Welded Joints with Ductile Cast Iron Joints

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    DOI:10.2355/tetsutohagane.TETSU-2018-158

    In this study fatigue experiments are conducted for ductile cast iron (DCI) to compare with the fatigue strength of cruciform welded joints. Here, several DCI specimens are prepared to have nearly the same fatigue strength in smooth specimens before welding and to have similar cruciform shapes in the welded joints. It is found that the fatigue strength of DCI specimen is about three times larger than that of the welded joint specimens. The fatigue strength improvement can be explained in terms of the small stress concentration factor, notch insensitivity and compressive residual stress generated by shot blasting for DCI joints.
  • Competition between Fatigue Crack Growth and Wear under Rolling – Sliding Contact Condition

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    DOI:10.2355/tetsutohagane.TETSU-2018-138

    A numerical model was developed to simulate the competition between crack initiation and growth by rolling contact fatigue (RCF) and wear in a railhead. The simulation model assumes that the materials are polycrystalline ferrite and pearlite and that RCF crack initiation is determined by the total accumulated plastic shear strain. The growth of short cracks is calculated using the Hobson model and the Archard model is used to calculate wear. In order to validate the developed model, twin disc rolling-sliding contact fatigue tests were performed. In the tests, rail material and slip ratio were changed and the crack initiation, crack growth and wear trace on the contact surfaces were investigated by SEM, EPMA and shape measuring instrument. Under these test conditions, simulations were performed using the developed model and compared the results. It was confirmed that the crack occurred at the nonmetallic inclusion/ferrite and ferrite/pearlite boundary at almost the same locations, therefore, the assumption of the model for the initiation was validated. It was also found that cracks of almost the same length and the direction existed in the vicinity of the contact surface at the same rolling cycles. Regarding wear, it was found that accurate analyses can be performed by considering the change of the contact pressure distribution and selecting an appropriate wear coefficient.
  • Thermodynamic Modeling of the SFCA Phase Ca2(Fe, Ca)6(Fe, Al, Si)6O20

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    DOI:10.2355/tetsutohagane.TETSU-2018-139

    The thermodynamic model of a silico-ferrites of calcium and aluminum solution, SFCA phase (Ca2(Fe, Ca)6Oct(Fe, Al, Si)6TetO20) was newly developed in the framework of the Compound Energy Formalism (CEF). Preferred substitution of Al atoms to tetrahedral sites in the SFCA solution was verified by X-ray absorption near edge structure (XANES) analysis. On considering crystallographic information in particular the short-range-ordering nature in the SFCA solution – the Ca8(Fe3+)20Oct(CaSi6+, FeFe6+, FeAl6+)3Paired(CaSi6+)1Paired(Fe3+, Al3+)20TetO80 structure was considered for modeling the SFCA solution. The optimized Gibbs energies of all end-members can successfully reproduce the experimental single phase region of the SFCA solution.
  • Effect of Laminated Structure on Mechanical Properties of Composition-modulated Co-Ni Laminated Plating

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    DOI:10.2355/tetsutohagane.TETSU-2018-140

    A composition-modulated Co-Ni laminated plating has been developed to extend the lifetime of molds used for continuous steel casting. We have investigated the relationship between the laminated structure and the mechanical properties of the plating films. The tensile strength of as-plated film increased with increasing thickness of the constituent layers, while the elongation did not depend on the thickness of the constituent layer and remained almost constant in the range from 3 to 5%. Heat treated at 400°C improved the tensile strength and the elongation. The improvement in the elongation was remarkable, and the elongation reached 13% in the film composed of layers with a thickness of 0.8 μm. The layer with low Ni content had an hcp structure, and that with high Ni content comprised two phases of the hcp and fcc structures in the as-plated state. By the heat treatment, the high Ni-content layer turned into the single fcc phase, while the low Ni-content layer kept the hcp phase, and accordingly, the film structure changed into the one where the lamination of the hcp and fcc layers was distinct. The fact that the fcc layers, which was easily deformed, were formed continuously in the lateral direction, was seemed to contribute to the significant improvement in the elongation after heat treatment.
  • Extraction of Phosphorus and Recovery of Phosphate from Steelmaking Slag by Selective Leaching

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    DOI:10.2355/tetsutohagane.TETSU-2018-128

    In steelmaking slag, phosphorus is distributed between liquid phase and solid solution of 2CaO·SiO2 and 3CaO·P2O5 at refining temperature. Using the difference in water solubility of the solid solution and the other phases, we are developing the process to separate phosphorus by acid leaching. In this paper, the optimum condition of leaching by nitric acid by the control of valency of Fe in slag was investigated and the recovery of phosphorus from leachate was also conducted. To dissolve the solid solution, pH has to be decreased to 3 and the solid solution containing FeO showed lower dissolution ratio. To suppress the dissolution of other phases in slag at this pH, slow cooling to avoid the formation of glassy phase was necessary. The artificially steelmaking slag with the appropriate composition was made and subjected to the leaching experiment. The dissolution ratio of phosphorus has reached about 91% and the phosphorus content in the residue was enough low. After the separation of residue, pH of the leachate increased to precipitate phosphate. At pH=7, 80% or more of the phosphorus in the leachate was precipitated and the phosphate content of the precipitate was about 25% after calcination.
  • Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel

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    DOI:10.2355/tetsutohagane.TETSU-2018-066

    In order to understand the cause of heat-to-heat variation in creep strength of Grade T91 steels, influence of initial microstructure on creep strength has been investigated. Distribution of chromium concentration considered to be a remained segregation was observed, corresponding to a lamellar contrast parallel to longitudinal direction of boiler tube. Standard deviation (SD) of ΔCr was employed as an indicator of degree of segregation, and good correlation was recognized between SD of ΔCr and creep rupture life at 650°C. Remained segregation was reduced by renormalizing heat treatment at not 1250°C, but 1200°C. Creep rupture life of the steel subjected to renormalizing heat treatment at 1200°C and tempering at 760°C, followed by normalizing and tempering with a standard heat treatment condition for Grade T91 steel, was prolonged for 2.3 to 2.8 times. Strengthening effect of renormalizing at 1200°C to reduce a remained segregation was confirmed by creep tests for up to about 10,000h at 600 and 650°C. Decreases in number density of M23C6 carbide particles, length of high angle boundaries and average KAM value during creep exposure have been promoted by a presence of remained segregation. Since diffusion is enhanced by concentration gradient of elements, degradation due to microstructural change is promoted by a presence of remained segregation. Segregation should be reduced to obtain high creep strength with homogenized concentration of chemical composition.
  • Effect of Heat Treatment on Peel Strength of 16Cr-Ferritic Stainless Steel / Aluminum Rolled Clad Sheet and Proposed Joint Mechanism

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    DOI:10.2355/tetsutohagane.TETSU-2018-133

    The peel strength of 16Cr-ferritic stainless steel / aluminum rolled clad sheet is improved by heat treatment at 300 to 500 °C after clad rolling. The joint mechanism was studied by analyzing the fracture surface after the peel test, taking into account the characteristics of the peel test method.The detailed investigation into the fracture surface after peel test allows us to classify fracture sites into three categories: 1) ductile fracture in aluminum base material, 2) flake-like fracture in 16Cr-stainless steel, and 3) fracture in the intermediate interface layer between aluminum and 16Cr-stainless steel. It was revealed that the intermediate layer breakage mainly occurs in the as-rolled clad sheet; whereas after heat treatment at 300 to 500°C, the aluminum base material breakage predominantly occurs.Close observation into the state of deformation at the crack tip of the peel tested specimen leads us to conclude that clad rolled and subsequently annealed aluminum undergoes plastic deformation during the peel test because significant softening easily takes place preferentially in aluminum during low temperature heat treatment. This might imply the decrease in peel strength by heat treatment, which is different from the fact. However, the load area responsible for peeling force during the peel test is inferred to substantially increase, which gives rise to the increase in peel strength. This is because the peel strength is simply evaluated by dividing the peel force by the width of the specimen.
  • 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.

Article Access Ranking

23 Mar. (Last 30 Days)

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  2. Comprehensive Optimization Control Technology of Rolling Energy and Oil Consumption in Double Cold Rolling ISIJ International Advance Publication
  3. Experiments on Removal of Hydrophilic Fine Particles in Bubbly Flow ISIJ International Vol.59(2019), No.2
  4. Effects of Impurities and Processing Conditions in Al–1%Mn Alloys on the Formation of Thermally Stabilized Substructures MATERIALS TRANSACTIONS Vol.59(2018), No.11
  5. Coating Film Profiles Generated by Fluctuating Location of the Wiping Pressure and Shear Stress ISIJ International Vol.59(2019), No.2
  6. Temperature Field Distribution of a Dissected Blast Furnace ISIJ International Advance Publication
  7. Evolution of Blast Furnace Process toward Reductant Flexibility and Carbon Dioxide Mitigation in Steel Works ISIJ International Vol.56(2016), No.10
  8. Effect of EAF Slag Temperature and Composition on its Electrical Conductivity ISIJ International Vol.59(2019), No.2
  9. Fundamentals of Silico-Ferrite of Calcium and Aluminium (SFCA) Iron Ore Sinter Bonding Phase Formation: Effects of Basicity and Magnesium on Crystallisation during Cooling ISIJ International Vol.59(2019), No.2
  10. Molecular Dynamics Simulation of Carbon Effect on the Thermal Physical Properties of the Molten Iron ISIJ International Vol.59(2019), No.2

Search Phrase Ranking

23 Mar. (Last 30 Days)

  1. blast furnace
  2. blast furnace permeability
  3. blast furnace productivity
  4. galvanizing
  5. tuyere abrasion
  6. tuyere erosion
  7. tuyere failure
  8. isij
  9. lme
  10. wear on tuyere