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

Tetsu-to-Hagané Advance Publication

  • Phase Equilibria in High Phosphate-Containing Slag without CaO Saturation at Elevated Temperature

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    DOI:10.2355/tetsutohagane.TETSU-2021-046

    Japan relies on imports for almost the entire amount of phosphorus, which is indispensable for human life and industrial materials. Therefore it is required to recover phosphorus from dephosphorization slag and sewage sludge which are promising unutilized phosphorus resources. Aiming wholesale recovery of phosphorus from the slag and sludge, a fundamental study on condensation of phosphorus in solid phase through high temperature phase separation was carried out. The experiments at 1573 K on principal [CaO-SiO2-P2O5] ternary model sample and Al2O3 and Fe2O3 added therein showed unsaturation with CaO and precipitation of solid 3CaO・P2O5 as the phosphorus-concentrated phase in all the sample. The contamination of the other components in 3CaO・P2O5 was low, especially less than 1 mass% for Al2O3 added samples. The liquid phase was also formed with Al2O3 or Fe2O3 addition, and the liquidus composition in quaternary samples were consistent with those appeared in [CaO-SiO2-Fe2O3] and [CaO-SiO2-Al2O3] ternary diagram. P2O5 content in the quaternary liquid phases were lower in Al2O3 added samples than those in Fe2O3 added samples. Such difference was discussed in terms of optical basicity and CaO activity for liquid phase. Due to the coexistence of solid SiO2 phase at Fe2O3 addition, the SiO2 content in liquid phase became lower compared to Al2O3 addition, and led to higher optical basicity, which would allow higher P2O5 capacity in liquid phase. These considerations strongly suggest that an effective control of composition would be key technology for the phosphorus recovery through condensation and separation of phosphorus concentrated phase.
  • Effects of Residual Stress on Hydrogen Embrittlement of a Stretch-Formed Tempered Martensitic Steel Sheet

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    DOI:10.2355/tetsutohagane.TETSU-2021-055

    The effects of residual stress on the hydrogen embrittlement behavior of a tempered martensitic steel sheet with 1-GPa-class tensile strength stretch-formed by a hemisphere punch simulating press-formed automotive structural parts were investigated. Cracking on the stretch-formed specimen induced by potentiostatic hydrogen charging was initiated in the foot of the impression of the specimen and propagated to the radial direction both toward the hillside and the plain. The mixture of quasi cleavage and intergranular fractures were observed whole through the fracture surface. Residual stress in the stretch-formed specimens was analyzed by using energy-dispersive X-ray diffraction method utilizing the synchrotron X-ray radiation at SPring-8. In addition, stress and plastic strain distributions in the specimen were an-alyzed by using Finite Element Method (FEM). These analyses depicted that the high tensile stress in the circumferential direction was in the foot of the impression, corresponding to the direction of the crack growth. The FEM analysis revealed that the high triaxial stress was in the foot suggesting accumulation of hydrogen. It was considered that the preferential crack initiation at the foot was promoted by the high residual stress in the circumferential direction and the hydrogen accumulation due to stress-induced diffusion.
  • Mass Gain Rates of Various Steels During Atmospheric Corrosion Under Cyclic Conditions of Dry and Controlled-humidity Air

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    DOI:10.2355/tetsutohagane.TETSU-2021-062

    Mass gain rates of various steels during atmospheric corrosion under cyclic conditions of dry and controlled-humidity air were investigated. Fe, SBHS500 carbon steel and SMA490AW weathering steel were selected for the test materials. A droplet of MgCl2 solution was set on the plate steel specimen. The specimen was exposed in the humidity-controlled air for about 82.8 ks and in the dry air for 3.6 ks. After the process, an area as well as a volume of the corroded part, surface appearance and a mass of the specimen were recorded. The process was repeated over 5000 ks of an accumulated wet time. Selected values of relative humidity were 75, 43 and 33%. For the Fe specimen, the condition of RH75% induced Region(i), (ii) and (iii), where Region(i) is the period in which a corroded area was independent of time and a mass of the specimen linearly increased with time, Region(ii) is the period in which an area and a mass increased more rapidly, and Region(iii) is the period in which increments of an area and a mass relatively decrease. The conditions of RH43% induced only the Region(i) and RH33% provided Region(ii) in addition to (i). A mass gain rate in Region(i) was larger under RH75% than those under RH43 and 33%. For the condition of RH75%, any of the three specimens showed the three regions, and a mass gain rate in Region(i) was a maximum for SBHS500 steel and a minimum for Fe.
  • Hydrogen Absorption Behavior and Absorbed Hydrogen Trapping Sites in Rolling Contact Fatigue

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    DOI:10.2355/tetsutohagane.TETSU-2021-018

    Hydrogen absorption behavior and microstructural change of carburized JIS SCr420 steels containing different amounts of retained austenite in rolling contact fatigue were investigated. The thermal desorption analysis confirmed hydrogen desorption at the second-peak between 423 and 623 K after rolling contact fatigue. The hydrogen concentration at the second-peak increased with number of cycles in the rolling contact. This increment was larger when using the steel with a higher amount of retained austenite before the fatigue test. The increment of hydrogen concentration at the second-peak was large even when the introduction of new dislocations due to the martensitic transformation of retained austenite was considered to be small. The activation energies of desorption for the second-peak hydrogen were calculated to be 50.6 kJ·mol−1 for the steel with 10.4% retained austenite and 55.8 kJ·mol−1 for the steel with 4.9% retained austenite. The activation energies of cathodically charged 0.8%C steels with 10.9% and 6.0% retained austenite, simulating carburized layer before the test, were 36.2 and 42.2 kJ·mol−1, respectively. This means that the activation energy of hydrogen desorption increased during rolling contact. The absorbed hydrogen during the rolling contact fatigue was likely trapped in more stable trapping sites related to the retained austenite which were formed under cyclic stress.
  • Micro-electrochemical Properties and Pitting Corrosion Resistance of Microstructures of Carbon Steels

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    DOI:10.2355/tetsutohagane.TETSU-2021-032

    This paper presents an introduction of the relationship between the electrochemical properties of microstructures and pitting corrosion resistance of carbon steels in chloride-containing near-neutral pH environments. Recent investigations by micro-scale electrochemical measurements have been demonstrated that the pitting corrosion resistance of typical microstructures was ordered as follows: (high) as-quenched martensite > primary ferrite > pearlite (low). In the case of pearlite, it has been reported that pits proceeded along the lamellar structure consisted of Fe3C and ferrite. On the other hand, in the case of martensite, according to the studies based on the first-principles calculations, it has been proposed that the superior corrosion resistance was related with the electronic interaction between Fe and interstitial C. It was reported that the electronic density of states of Fe around the Fermi level decreased by the presence of interstitial C.
  • Addition Effect of Aromatic Amines on Coal Fluidity and Coke Strength

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    DOI:10.2355/tetsutohagane.TETSU-2021-016

    Coal fluidity is an important parameter in coal blending techniques for coke making because it strongly influences coke qualities. On the other hand, recently, the amount of high fluidity coal has been limited. To cope with this problem, caking additive method which improves fluidity of coal has been developed and commercialized. However, since tight supply of high fluidity coal is anticipated in the future, it is of great importance to develop more effective caking additive. Therefore, in this study, we investigated effect of 11 kinds of polyaromatic hydrocarbons which include oxygen, sulfur and nitrogen containing compounds on coal fluidity in order to search for more effective chemical substances. The additives were added to low fluidity coal, and fluidity analyses were carried out according to the Gieseler plastometer method. Addition of sulfur and oxygen containing compounds lowered fluidity of coal, whereas addition of aromatic amines enhanced fluidity of coal. Coal fluidity ameliorated with increasing the molecular weight of aromatic amine, and N, N'-di-2-naphthyl-1, 4-phenylenediamine (DNPD) was the most effective aromatic amine in this study. Carbonization tests in an electric furnace were conducted to investigate an effect of DNPD on coke strength. As a result of adding only 1 wt% DNPD, fluidity of blended coal and coke strength (Drum Index) were highly improved.
  • Quantitative Reduction of Iron under Nitrogen Atmosphere for Potassium Dichromate Titration

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    DOI:10.2355/tetsutohagane.TETSU-2021-019

    Total iron contents in iron ores have been accurately determined by JIS M 8212, in which iron ions in digested solutions of iron ores are reduced to divalent prior to redox titration. It is necessary for the iron reduction process that no reducing chemicals other than iron(II) in the decomposition solutions must not remain after the reduction with titanium(III). However, the redox reactions concerning the chemical species present in the decomposition solution has not been completely elucidated at the present time. In this paper, the redox reactions that occurred in the decomposition solution during the iron reduction in JIS M 8212 were studied by potentiometry and spectrophotometry under nitrogen atmosphere. The redox reaction of tin(II)/(IV) was very slow, causing significant effects on identifying the end point of the indicator for the iron reduction. The copper chloro-complexes were reduced with titanium(III) at a potential higher than that of indigo carmine used as a redox indicator, so that the reduced copper(I) gave a positive error to the potassium dichromate titration. The pen-tavalent vanadium was reduced with titanium (III) to form a complex with titanium, which also interfered with the potassium dichromate titration positively. To avoid these interferences, titanium(III) chloride was stoichiometrically added to the reaction mixture after addition of tin(II) chloride under nitrogen atmosphere so as to reduce only iron to divalent prior to the following redox titration. Combination of the proposed protocol with the potassium dichromate titration could successfully determine the iron content of certified reference materials of iron ores.
  • Selection of the Massive-like δ-γ Transformation due to Nucleation of Metastable δ Phase in Fe-18 mass%Cr-Ni Alloys with Ni Contents of 8, 11, 14 and 20 mass%

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    DOI:10.2355/tetsutohagane.TETSU-2021-020

    It has been realized that a massive-like transformation, in which δ phase (ferrite) transformed to γ phase (austenite) in the solid state during and after solidification, was selected in Fe-C steels. X-ray radiography confirmed that the massive-like transformation also occurred in Fe-18 mass%Cr-Ni alloys with Ni contents of 8, 11, 14 and 20 mass%Ni. According to the equilibrium phase diagram, δ phase is the primary phase in 8 and 11 mass%Ni alloys while γ phase in 14 and 20 mass%Ni alloys. Solidification was always initiated by nucleation of δ phase and consequently fine γ grains were formed by the massive-like transformation in 8 and 11 mass%Ni. On the other hand, nucleation of δ phase as a metastable phase was preferably selected at lower undercoolings (<50 K) in 14 and 20 mass%Ni and consequently the massive-like transformation occurred even in 14 and 20 mass%Ni alloys. Solidification of γ phase can be triggered by nucleation of δ phase followed by the massive-like transformation in the Fe-Cr-Ni with lower Cr/Ni values (the primary γ alloys). Moreover, the present study demonstrates that the massive-like transformation will be commonly observed in Fe-based alloys, in which δ and γ phases are competitive each other from a thermodynamic perspective.
  • Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation

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    DOI:10.2355/tetsutohagane.TETSU-2021-009

    tting occurred after the wet-dry corrosion test, and calcium and sulfur were detected near the center of the pit. From the results of the microscale polarization measurements, the pitting initiation sites for the SBHS500 steel were determined to be the CaS inclusions. No pitting was observed at the microscale electrode area without inclusions. In a boric-borate buffer solution containing 10 mM NaCl, the depassivation pH at the microscale electrode area without inclusions was 6.0. The depassivation at the microscale electrode area with the CaS inclusions occurred at approximately pH 6.6. The CaS inclusions in the SBHS500 steel were found to be a trigger of the depassivation of the steel matrix surrounding the inclusions.
  • Mechanism and Suppression Method of Hydrogen Entry into Steel by Blasting

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    DOI:10.2355/tetsutohagane.TETSU-2020-124

    The effect of blasting on hydrogen analysis was investigated with the aim of establishing a hydrogen analysis method for precisely measuring hydrogen that entered steel in a corrosive environment. The hydrogen existing states of the specimens blasted under various conditions were analyzed using thermal desorption analysis and the hydrogen visualization method by secondary ion mass spectrometry. The phenomenon of hydrogen entry into steel by blasting was demonstrated for the first time. It should be noted that the effect is remarkable in the case of a specimen with a large specific surface area, and the blasting becomes an inhibitory agent in the measurement of the hydrogen content in steel. The hydrogen source for increasing the hydrogen content due to blasting is mainly the water contained in the abrasive. The mechanism of increasing the hydrogen content in steel by blasting is that the fresh surface of the steel exposed by blasting reacts with the water in the abrasive, which results in the hydrogen generation and entry into steel. Additionally, the water in the abrasive remaining on the steel surface reacts with steel during the thermal desorption analysis to release hydrogen. To suppress the increase of hydrogen content by blasting, it is effective to use abrasive with low water content and to remove rust by repeating a short blasting time in order to suppress the temperature rise of the specimen.
  • Selective Separation of Metallic Fe Remaining in Slags Using Electrical Pulse Disintegration

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    DOI:10.2355/tetsutohagane.TETSU-2021-008

    Metallic Fe (hereinafter abbreviated as M.Fe) is suspended in steelmaking slags due to the stirring action during blowing and is mainly recovered via pulverization, classification, and magnetic separation. However, steelmaking slags are hard, and it is difficult to transform irregular-shaped and fine M.Fe in slags into free particles through the conventional pulverization method, which requires a large energy consumption. In this study, pulverization and separation experiments of steelmaking slags were performed using electrical pulse disintegration, which is completely different from the conventional pulverization method and capable of causing preferential fracture at the heterophase interface. As a result, several free particles of M.Fe with almost no slag attached were obtained from the coarse and fine pulverized particles. In addition, the electric field analysis results of a system where spherical M.Fe exists in a slag show that electric field concentration occurs in the front and back directions of the external magnetic field. The findings also show that a fracture can occur at the interface between the M.Fe and slag due to the combination of increased discharge probability, concentration of thermal energy, and generation of the Maxwell stress. Furthermore, the larger the pulverized mass, the higher the pulverization efficiency. In sum, electrical pulse disintegration may be advantageous for actual operations, where large quantities of oxides employed in the steel industry, such as steelmaking slag, spent refractories, and raw materials, should be treated in a short time with low energy consumption.
  • Delayed Fracture Evaluation of Highstrength Steel Sheets Using the Hydrogen Permeability

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    DOI:10.2355/tetsutohagane.TETSU-2021-001

    The application of high-strength steel sheets in automobiles has been increased to achieve low bodyweight and simultaneously enhance crashworthiness. High-strength steel sheets are susceptible to hydrogen embrittlement and it is essential to evaluate their delayed fracture resistance for appropriate use. Delayed fracture resistance is typically evaluated using the relationship between the amount of diffusible hydrogen and fracture strength obtained from a constant load test and the slow strain rate technique (SSRT). It is difficult to monitor the amount of diffusible hydrogen invading from the environment; the thermal desorption analysis is not a non-destructive analysis to obtain the amount of diffusible hydrogen and diffusible hydrogen is easily desorbed from the specimens. The hydrogen permeation test easily monitors the invasion of diffusible hydrogen. In this study, we evaluated the delayed fracture resistance of high-strength steel sheets using the hydrogen permeability obtained from the hydrogen permeation test. As a result, relationships between hydrogen permeability, mechanical properties obtained from SSRT, and the brittle fracture surface ratio were found to be consistent among various hydrogen invasion conditions, such as under hydrogen charging and corrosive environments. Furthermore, little diffusible hydrogen was detected using the hydrogen permeation test. Thus, delayed fracture resistance obtained from the relationship between hydrogen permeability and its mechanical properties proves the effectiveness of this method.

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19 Jun. (Last 30 Days)

  1. blast furnace
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  8. 錬鉄
  9. contact angle
  10. hydrogen-assisted crack propagation in pre-strained twinning-induced plasticity steel: from initiation at a small defect to failure