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ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Advance Publication

  • Improvement of Shape Memory Effect by Optimizing Thermal and Mechanical γ → ε Martensitic Transformation by Hot Rolling

    Takahiro Sawaguchi, Ilya Nikulin, Yuya Chiba, Susumu Takamori

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    DOI:10.2355/isijinternational.ISIJINT-2021-212

    Abstract

    We propose a new concept to improve functional/mechanical properties of Fe-high Mn alloys, by suppressing thermal γ → ε martensitic transformation with a proper thermo-mechanical treatment. As an experimental example to demonstrate the validity of this concept, we tried to improve the shape memory effect of a Fe-15.3Mn-5.8Si-0.24C (mass-%) alloy by hot rolling. The alloy showed a dual γ/ε phase at room temperature (Ms = 66°C) and a poor shape recovery strain of approximately 0.6% after the solution-treatment. The pre-existing thermal ε-martensite can act as obstacles against the reversible forward-reverse γ → ε martensitic transformation under loading and subsequent heating. Hot rolling at 800°C with a 70% reduction appeared to dramatically improve the shape recovery strain up to 2.9%. The rolling suppressed thermal γ → ε martensitic transformation during cooling to obtain the single γ-phase at room temperature. Further annealing of the 800°C -rolled specimen at 800 to 1000°C or rolling at 600°C deteriorated shape recovery strain to about 1%. The rolling at 400°C made the alloy brittle.

  • Effect of Tundish Flux on Compositional Changes in Non-metallic Inclusions in Stainless Steel Melts

    Tae Sung KIM, Sang-Beom LEE, Joo Hyun PARK

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    DOI:10.2355/isijinternational.ISIJINT-2021-167

    Abstract

    The effect of the tundish flux on the evolution of non-metallic inclusions in Si-killed 304 (18%Cr-8%Ni) stainless steel has been investigated at 1773 K. The interfacial reaction between molten steel and the CaO–Al2O3–MgO flux causes the aluminum pick-up from the liquid slag into the steel melt, resulting in a decrease in the oxygen content in the steel. The aluminum originating from the slag modifies the pre-existing Mn-silicate inclusions into alumina-rich inclusions in the steel. Because the oxygen content in the steel decreases as it reacts with the CaO–Al2O3–MgO flux, the degree of supersaturation for alumina formation is too low to precipitate new-born alumina particles in the steel. By analyzing the population density function (PDF) results for inclusions, it can be observed that the growth of spinel-type inclusions occurs by the diffusion of aluminum and magnesium in the steel. On the other hand, the composition of the steel, as well as the evolution of inclusions, is negligibly changed when the CaO–SiO2–MgO flux is added to the molten steel. Furthermore, the computational simulation for predicting the evolution of inclusions in molten steel during a continuous casting tundish process was carried out based on a refractory-slag-metal-inclusion (ReSMI) multiphase reaction model.

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  • Improvement of Carbothermic Reduction of Copper Smelting Slag and Valuable Constituents Recovery

    Guang Wang, Hongqiang Zhang, Jingsong Wang, Qingguo Xue

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    DOI:10.2355/isijinternational.ISIJINT-2021-136

    Abstract

    In order to comprehensively utilize copper smelting slag, the effect of strengthening measures on the reduction rate of the copper smelting slag, reduction kinetics, magnetic separation of reduced pellet and volatilization of residual valuable constituents were investigated in the present study. Milling for mechanical activation was the most efficient method to improve the reduction rate of copper smelting slag compared to addition of Na2CO3 catalyst and high reactivity reducing agent. The metallization degree of reduced pellet increased from 54.5% to 75.5% when the slag-coal mixture was milled for 30 s and reduced at 1100°C for 30 min. The apparent activation energy for the reduction of milled pellet increased from 96.1 kJ/mol to 153.5 kJ/mol. The iron concentrate magnetically separated from the milled pellet reduced at 1200°C had the best quality. The removal rates of typical elements during direct reduction-magnetic separation decreased in the sequence of Zn>K>Na>Cu. Secondary-dust captured from the flue gas contained 70.17 mass% Zn and 11.99 mass% Pb, which could meet the requirements of I grade zinc ore. The Zn in the dust existed in the form of ZnO. The productivity of the dust was around 1.49%. The application of mechanical milling in the reduction of copper smelting slag/coal composite pellet can improve the reduction efficiency of iron oxide and the quality of Zn-rich secondary dust. This work can help to enhance the utilization of copper smelting slag in a more efficient and sustainable method.

  • Feasibility Study of Visualizing Strain Distributions Using Opal Film

    Yoshikazu Tanaka, Hiroshi Fudouzi, Tsuyoshi Hyakutake

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    DOI:10.2355/isijinternational.ISIJINT-2021-383

    Abstract

    This paper presents a feasibility study of visualizing the strain distribution of structural elements using opal film. Opal film with an initial peak wavelength of 510 nm was employed in tensile and four-point bending tests to evaluate the feasibility of visualizing the strain distribution using this type of film. The experimental results of the tensile and four-point bending tests show that the peak wavelength has a linear relationship with the first invariant of the strain. The slope of the experimentally obtained relationship between these variables showed good agreement with the theoretically predicted slope. In the four-point bending test, visualization of the first invariant of the strain using opal film was successfully demonstrated, thereby confirming the feasibility of strain visualization using opal film.

  • Wear and Corrosion Resistance of CrN Films on Oxynitriding-treated Vanadis 8 Tool Steel via the DC Magnetron Sputtering Process

    Shih-Hsien Chang, Meng-Hsun Yu, Kuo-Tsung Huang

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    DOI:10.2355/isijinternational.ISIJINT-2021-318

    Abstract

    This research coated CrN films on oxynitriding-treated Vanadis 8 tool steel using the DC magnetron sputtering process of the PVD technique. The experimental parameters include different gas flow rates (Ar/N2 was 20/20, 24/16, 28/12, and 32/8, respectively), with a bias of -50 V, power of 100 W, deposition temperature of 300°C, and deposition time of 180 min, respectively. The experimental results show that Vanadis 8 tool steel can form an effective oxynitriding layer with a depth of about 50 µm after the oxynitriding treatment, and the surface hardness increased to about 1400 HV0.05. Furthermore, the duplex coating layers exhibited optimal properties when the CrN films treated at an appropriate gas flow rate of Ar/N2 was 24/16. Meanwhile, according to XRD analysis, the coating layer has a relatively high content of CrN composition, as well as the best wear resistance (the lowest specific wear rate when the loads of 2 N and 4 N were 2.05 × 10-5 and 1.56 × 10-5 mm3·m-1·N-1) and good corrosion resistance (in a 3.5 wt% NaCl environment, Icorr = 3.05 × 10-4 A·cm-2, Rp = 362.52 Ω·cm2). Overall, this study reveals that the CrN/oxynitriding duplex surface treatment could effectively improve the wear and corrosion properties of Vanadis 8 tool steel.

  • Cleanliness and Control of Inclusions in Al-Deoxidized Bearing Steel Refined by Basic Slags during LF-VD-Ar Bubbling

    Min Jiang, Kai-lun Li, Rui-gang Wang, En-jiao Yang, Xin-hua Wang

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    DOI:10.2355/isijinternational.ISIJINT-2021-306

    Abstract

    Cleanliness and control of inclusions in Al deoxidized bearing steel were studied by industrial trials, in which three basic slags were used in the LF-VD-Ar bubbling refining process. With basicity (mass ratio of CaO/SiO2) about 3.9–4.2, 5.2–6.5 and 6.9–7.1 while Al2O3 about 30.9–32.5 mass%, 37.2–40 mass% and 29.8–30.4 mass%, T.O content in steel after Ar bubbling was 0.0006 mass%, 0.0007 mass% and 0.0004 mass%, respectively. During the refining, inclusions experienced the evolution from Al2O3 into spinel and finally into CaO–MgO–Al2O3. By comparison, inclusions were more desirably controlled when slag basicity and Al2O3 contents were about 6.9–7.1 and 29.8–30.4 mass%, with lowest number density, smaller sizes within 20 µm and average composition in liquid region. Particularly, after Ar-bubbling, pick-ups in the number density of inclusions were observed for the three heats of trials and large inclusions (even exogenous inclusions over100 µm) were often seen in heat 2. The obtained results prompted the risk of large inclusions in bearing steel in Ar bubbling, which were detrimental to fatigue lives of bearing.

  • Effect of BaO on Formation Mechanisms of Silico-ferrite of Calcium and Aluminum

    Jian-tao Ju, Ke Ma, Xiang-Dong Xing, Gui-qing Zhao

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    DOI:10.2355/isijinternational.ISIJINT-2021-240

    Abstract

    Silico-ferrites of calcium and aluminum (SFCA) are formed during the sintering process, and their changes are critical to the quality of the sinter. Aiming to further clarify the effect of BaO (0 mass%, 1 mass%, 2 mass%, 3 mass%, 5 mass%, 7 mass%, and 9 mass%) on the bonding process of SFCA. In this work, X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), thermogravimetry-differential scanning calorimeter (TG-DSC) were used to analysis the formation mechanisms of SFCA. The results indicated that the main bonding phase was SFCA. In addition, SFCA-I, CF, C2F, and silicate existed in the BaO-free sinter. Adding a small amount of BaO (up to 2 mass%) could increase the decomposing temperature of SFCA and increase the formation of the needle-like SFCA. With the increase of BaO adding from 2 to 9 mass%, the BaFe12O19 (FB) formed could reduce the decomposing temperature of SFCA, which deteriorated the quantity of sinter. And, BaO can promote the formation of C2F in the CF and C2F system, which decreased the eutectic melting temperature of CF and C2F.

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  • Material Modeling of Hot-Rolled Steel Sheet Considering Differential Hardening and Hole Expansion Simulation

    Shunya Nomura, Toshihiko Kuwabara

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    DOI:10.2355/isijinternational.ISIJINT-2021-365

    Abstract

    The elastoplastic deformation behavior of a 440-MPa hot-rolled steel sheet subjected to many linear stress paths is precisely measured using biaxial tensile tests with cruciform specimens (ISO 16842: 2014) and multiaxial tube expansion tests to determine appropriate material models for finite element analysis (FEA). It is found that the Yld2000-2d yield function correctly reproduces the contours of plastic work and the directions of the plastic strain rates. Differential hardening (DH) models are determined by varying the values of the exponent and material parameters for the Yld2000-2d yield function as functions of the reference plastic strain. Moreover, a finite element analysis of hole expansion in the test material is performed. The DH model correctly predicts the minimum thickness position, which matches the fracture position of the specimen in the experiment.

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  • Inhomogeneity of Plastic Deformation after Yielding in Low-carbon Martensitic Steels

    Masaki Tanaka, Tatsuya Morikawa, Shimpei Yoshioka, Katsutoshi Takashima, Shinjiro Kaneko

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    DOI:10.2355/isijinternational.ISIJINT-2021-287

    Abstract

    The effect of tempering on uniform elongation was investigated for fully lath martensitic steels with 0.2% C by mass. Stress–strain curves were obtained from specimens tempered at 100, 200, 300 and 400°C. Although total elongation rarely depends on the tempering temperature, the uniform elongation decreased while local elongation increased with the tempering temperature. It was found, using precision markers drawn on the specimen surface, that the distribution of the equivalent plastic strain developed during uniform deformation was inhomogeneous in the specimen tempered at 200°C and relatively homogenous in the specimen tempered at 300°C. Finite element analysis suggests that the uniform elongation depends on the volume fraction that continues elastic deformation even after macroscopic yielding. Therefore, the experimental results showing a decrease in the uniform elongation with tempering temperature can be explained by the decrease in the volume fraction that continues elastic deformation immediately after the macroscopic yielding, which is a deformation character specific to low temperature tempered martensitic steels. The range of variation in nanohardness decreased with the tempering temperature, suggesting that the variation in the local yield stress also decreases with the tempering temperature.

  • High Temperature Softening and Melting Interactions Between Newman Blend Lump and Sinter

    Mohammad Mainul Hoque, Hamid Doostmohammadi, Subhasish Mitra, Damien O’dea, Xinliang Liu, Tom Honeyands

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    DOI:10.2355/isijinternational.ISIJINT-2021-198

    Abstract

    In this work, the softening and melting (S&M) behaviour and whole blast furnace (BF) performance of Newman Blend Lump (NBLL), plant sinter, and sinter-NBLL mixture were studied using S&M under load test and numerical BF modelling. Both physical and chemical interactions between sinter and lump were confirmed in the S&M process. Significant improvements were found in the S&M behaviour of the sinter-NBLL mixture because of the physical and chemical interaction. The physical interaction was examined using X-ray/Neutron Computed Tomography (CT) scanning on the samples from interrupted S&M under load tests. The void fraction in the ferrous layer of the sinter-NBLL mixture was found to be similar to the sinter and was higher than that for NBLL. The chemical interaction was investigated by analysing the Ca transfer from sinter to NBLL, which indicated that Ca transfer started around 1200°C in the S&M process. FactSage was used to assist in the interpretation of the S&M test results. It was found that the NBLL sample starts to melt at a lower temperature compared to other burdens used in the present study, which also agreed well with the CT scan results. The whole BF performance of different ferrous burdens was studied using the experimental results as inputs. The sinter-NBLL mixture behaved more like the sinter than the NBLL; compared with the sinter only burden with the same total basicity, the sinter-NBLL combination formed a more permeable CZ, had a lower total BF pressure drop, and a higher gas utilization rate.

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  • Characterization and Optimization of Pearlite Microstructure Using Persistent Homology and Bayesian Optimization

    Kazuki Kiyomura, Zhi-Lei Wang, Toshio Ogawa, Yoshitaka Adachi

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    DOI:10.2355/isijinternational.ISIJINT-2021-197

    Abstract

    Pearlite spheroidization is substantially a spatial-geometric evolution of cementite. In this study, a persistent homology analysis was employed to characterize the topological features of cementite component of pearlite steel, through which the lamellar and spherical pearlite microstructures were successfully distinguished. Because the mechanical performance of pearlite steel is highly sensitive to the cementite configuration, an inverse conversion of persistent-homology digital data to an image for some properties of interest was proposed by using Bayesian optimization. The proposed microstructural optimization approach paves a way to interpret persistent-homology information in metallurgy and presents the feasibility of data-driven persistent-homology-based property predictions and microstructural optimization.

  • Influence of Annealing Microstructure on the Low-cycle Fatigue Properties and Fatigue Microstructure of a Fe–15Mn–10Cr–8Ni–4Si Seismic Damping Alloy

    Ilya Nikulin, Takahiro Sawaguchi, Fumiyoshi Yoshinaka, Susumu Takamori, Yuuji Kimura

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    DOI:10.2355/isijinternational.ISIJINT-2021-211

    Abstract

    We investigate the effects of the annealing microstructure on the low-cycle fatigue (LCF) life (Nf), cyclic stress behaviour and fatigue microstructure of a Fe–15Mn–10Cr–8Ni–4Si alloy that exhibits a deformation-induced transformation of austenite (γ-phase) into ε-martensite (ε-phase). The alloy rolled at 800°C was annealed at 600°C, 700°C, 800°C and 900°C to vary the grain size, the fraction of recrystallised grains and the texture intensity. Fully reversed axial strain-controlled LCF tests were conducted at total strain amplitudes, Δεt/2, ranging from 0.007 to 0.02. The alloy showed a higher Nf than common steels and ferrous high-Mn alloys in this strain range. This type of annealing microstructure was found to impact the Nf, fatigue behaviour and deformation-induced ε-martensitic transformation (ε-MT) in the studied alloy. The fully recrystallised and weakly textured austenite formed at T ≥ 800°C facilitated the uniform development of ε-martensite under cyclic deformation and led to an increased Nf. The partially recrystallised and textured austenite-containing substructure with high dislocation density formed at T ≤ 700°C suppressed the ε-MT, retarded reversible dislocation motions in the un-recrystallised regions and moderately decreased Nf. Moreover, Nf and the deformation-induced ε-MT were observed to be less sensitive to variations in grain size.

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  • Three-dimensional Quantitative Evaluation of the Lamellar Curvature in Pearlitic Steel Based on an Orientation Analysis of Cementite

    Makoto Kosaka, Kohsaku Ushioda, Toshihiko Teshima, Minoru Nishida, Satoshi Hata

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    DOI:10.2355/isijinternational.ISIJINT-2021-194

    Abstract

    To quantitatively evaluate the three-dimensional lamellar curvature in pearlitic steel, the crystallographic orientation rotation of ferrite and cementite was analyzed using scanning electron microscopy and electron backscattering diffraction. In the hypereutectoid steel containing 0.92% C, 0.30% Mn, 0.20% Si, and 0.19% Cr, the ferrite–cementite interfaces in some colonies were confirmed to match well with those having frequently observed habit planes with the Pitsch–Petch orientation relationship. It was also confirmed that the ferrite and cementite near the ferrite–cementite interface rotated toward the same orientation to maintain the Pitsch–Petch orientation relationship and the habit plane. Based on the confirmation that the ferrite–cementite interface is well approximated by (010) plane of the adjacent cementite, the lamellae were revealed to have three-dimensional anisotropic curvature.

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  • Influence of Slag Viscosity and Composition on the Inclusion Content in Steel

    Dali You, Christian Bernhard, Alexander Mayerhofer, Susanne Katharina Michelic

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    DOI:10.2355/isijinternational.ISIJINT-2021-213

    Abstract

    Influence of slag viscosity and composition on the inclusion content in the steel is studied using laboratory experiments and modeling simulations. The steel samples are taken during the experimental process to record the inclusion content change. Afterwards the prepared samples are analyzed using automated scanning electron microscope and energy dispersive spectroscopy (SEM/EDS) method. A simple steel/slag reaction model is constructed based on the effective equilibrium reaction zone (EERZ) method. The inclusion content evolution process is discussed by combining the experimental and calculated results. It is found that the inclusion content evolution in the steel is determined by the inclusion generation and removal.

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  • Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

    Yuuji Kimura, Tadanobu Inoue

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    DOI:10.2355/isijinternational.ISIJINT-2021-068

    Abstract

    Ultrafine elongated grain (UFEG) structure with a strong <110>//rolling direction fiber texture was created for a 0.4%C-2%Si-1%Cr-1%Mo steel (mass%) through deformation of tempered martensite using multi-pass caliber rolling at 773 K with a rolling reduction of 78% (i.e. warm tempforming). Annealing of the warm tempformed steel at 843 K enhanced delamination toughening at lower temperatures without a significant loss of tensile strength at 1.8 GPa. It was suggested that delamination toughening was controlled through the precipitation of nanoscale Mo-rich precipitates in the UFEG structure.

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  • Viscosity Evaluation of Simulated Foaming Slag via Interfacial Reaction at Room Temperature

    Shota Hatano, Shogo Hayashi, Noritaka Saito, Kunihiko Nakashima

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    DOI:10.2355/isijinternational.ISIJINT-2020-640

    Abstract

    CaO-based slag used in hot metal pretreatment and converters in steelmaking processes typically contains dispersed gas phases. This is called foaming slag, which is known to degrade the quality of slag. The rheological behavior of this slag is dependent on the dispersed part of the gas phase. This gas is generated by the chemical reaction between the hot metal and the slag. In this study, simulated foaming slag was prepared by reacting sodium hydrogen carbonate and oxalic acid in glycerol, which disperses carbon dioxide. Next, we systematically investigated the effects of the volume fraction of the dispersed gas phase and the proportion of glycerol on the viscosity and bubble diameter. According to the model used in this study, the bubbles were smaller than those in the model in which the gas was directly dispersed. The bubble size increased as the gas phase ratio and liquid viscosity increased, likely because the bubble growth is promoted by increase in the gas phase ratio and liquid phase viscosity, and the frequency with which the bubbles contact one other. The increase of the gas phase ratio at low liquid-phase viscosity and low shear rate caused an increase in both apparent viscosity and relative viscosity, which was obtained by dividing the apparent viscosity by liquid-phase viscosity. However, these increases in viscosity were not observed at a high shear rate. This is likely because the mechanism of bubble diffusion and flow is affected by the liquid-phase viscosity and shear rate. We found that the model in this study exemplified a Herschel-Bulkley fluid. In addition, we proposed an equation for measuring viscosity from the gas phase ratio.

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  • Dissolution of Iron Oxides Highly Loaded in Oxalic Acid Aqueous Solution for a Potential Application in Iron-Making

    Phatchada Santawaja, Shinji Kudo, Atsushi Tahara, Shusaku Asano, Jun-ichiro Hayashi

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    DOI:10.2355/isijinternational.ISIJINT-2020-726

    Abstract

    Oxalic acid has been identified as a sustainable chemical enabling an efficient recovery of target metals from industrial minerals by dissolution. The dissolution process recently has attracted attention as a key reaction in a potential clean iron-making. In this application to efficiently produce a high-purity iron, the dissolution is required to occur in the absence of light, with no addition of other chemical reagents, and to produce high concentration iron oxalate aqueous solution as fast as possible. To reveal the chemistry of iron oxide dissolution for this application, in the present study, the dissolution experiments are carried out under various conditions with a particular focus on the iron oxide highly loaded in the oxalic acid aqueous solution. Highly acidic oxalic acid solution for dissolving the highly loaded iron oxide enabled the production of iron oxalates aqueous solution with the concentration of up to 0.56 mol-Fe/L. Different from conventional studies under diluted conditions with pH control, the dissolution followed a non-reductive mechanism, producing [Fe3+HC2O4]2+ as a dominant iron species, and highly correlated with a concentration of proton in the solution. The experimental results and proposed stoichiometries identified a minimum amount of oxalic acid required for the complete dissolution of iron oxide independently from the concentration and type of loaded iron oxide. Among iron oxides tested (α-Fe2O3, FeOOH and Fe3O4) as the feedstock, Fe3O4 had an advantage in the dissolution rate, but showed a relatively low iron recovery in the solution (80–90%) because of an unavoidable formation of FeC2O4·2H2O precipitates.

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  • An Empirical Comparative Study of Renewable Biochar and Fossil Carbon as Carburizer in Steelmaking

    Ryan ROBINSON, Liviu BRABIE, Magnus PETTERSSON, Marko AMOVIC, Rolf LJUNGGREN

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    DOI:10.2355/isijinternational.ISIJINT-2020-135

    Abstract

    Approximately 60–70% of the direct greenhouse gas emissions in electric arc furnace (EAF) steelmaking originate from the use of fossil carbon charge during melting of steel scrap. Regarding short-term solutions to mitigate the climate impact of steelmaking, there is greater potential to replace fossil carbon charge with renewable carbon in the EAF than in integrated blast furnace steelmaking where mechanical strength requirements on carbon charge are too demanding. Therefore, the present study aims to provide an experimental and practical foundation for using renewable biochar in the EAF as a relatively simple step to decrease the climate impact of steelmaking.In order to evaluate the inherent performance of biochar as a carburizing agent, lab-scale tests where completed using four different types of carbonaceous materials: synthetic graphite, anthracite coal and two types of biochar from woody biomass (BC1 and BC2). The first order dissolution rate constants from experiments ranged between 0.7 to 1.9 × 10-4 m/s, which agrees well with previously reported results. Furthermore, lab-scale results show that biochar properties commonly seen as detrimental, such as low carbon crystallinity and high porosity, do not necessarily constitute a disadvantage for biochar utilization as carburizer in steelmaking.In order to further assess the results from lab-scale tests, an industrial trial including six consecutive heats was performed in a 50 t EAF at the Höganäs Halmstad Plant. Results show that 33% substitution of standard Anthracite carbon charge with biochar BC2 gave no deviation from normal operating conditions in the EAF.

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