The 10 most-cited articles in 鐵と鋼 : 日本鐡鋼協會々誌, 2021

X-ray diffraction analysis is one of powerful tools on the dislocation analysis and this method can be applied reasonably for many metals with isotropic crystal structure such as bcc and fcc. In this study, modified Williamson-Hall analysis was applied for martensitic steels containing 0.006 – 0.26 mass% carbon and proved that the value of dislocation density increases with increasing the carbon content. However, martensitic steels containing solute carbon have bct structure characterized by different lattice constants on a-axis and c-axis. With increasing solute carbon, a-axis shrinks but c-axis is elongated. This leads to the peak séparation in an X-ray diffraction peak and causes an increase of the full-width at half-maximum (FWHM) in the diffraction peak. This suggests that the value of dislocation density is over estimated due to the effect of peak separation in as quenched martensitic steels with solute carbon. It was found that the increment of apparent dislocation density Δρ’ is expressed by the following equation as a function of the amount of solute carbon (mass%C),…

Electrodeposition of Zn-Ni alloy was performed on a Cu electrode at a current density of 10–5000 A·m−2 and a charge of 5 × 104 C·m−2 in an unagitated zincate solution at 293 K containing the reaction product of epichlorohydrin and imidazole as brightener. The effect of brightener on the deposition behavior of Zn-Ni alloy was investigated. The transfer current density at which the deposition behavior shifts from the normal type to anomalous was 50 to 100 A·m−2 in brightener-free solution, while it became 10 to 20 A·m−2 with an addition of brightener, indicating that the brightener greatly decreased the transfer current density. The transfer current density corresponded to the current density at which the potential of total polarization curve significantly shifted from the more noble region than the equilibrium potential of Zn to less noble region. With an addition of brightener, the decrease in transfer current density is attributed to suppression of hydrogen evolution, and the current efficiency for alloy deposition at high current density region decreased due to suppression of both…

It is important to improve fatigue life for pitting of gear in order to attempt down-sizing of gear unit and low fuel consumption. Rolling and sliding contact fatigue under high pressure in carburized SCM420 steel is studied. The ultimate aim is to understand the effect of material properties on the fatigue life. In this research, there was considerable interest in change of the material in the contact surface of specimens depending on the shift in tangential force acting on a moving roller in the direction of a tangent to the path of the roller during the fatigue test. Three lubricants were used in these fatigue tests for the purpose of changing the degree of tangential force. A roller tested under a lubricant that the tangential force is shifted higher compared with that of the other lubricant produced a pitting failure earlier. The roller also promoted to decrease the hardness and to narrow the half width of the (211) peak of alpha iron at the contact surface. The transition of these characteristics related to the creation of fine grain layer. That is regarded as worked structure…

In the steels with different particle dispersion, particle dispersion strengthening Δσ was theoretically estimated by Orowan model and Ashby-Orowan model. The comparison of experimental data with theoretical values proved the reasonability of Orowan model rather than Ashby-Orowan model. In Ashby-Orowan model, the line tension coefficient of dislocation is evaluated much smaller and this leads to the under-estimation of Δσ. It was also confirmed that there is no effect of grain size on 0.2% proof stress of the steels used. As a result, it is concluded that the yield stress of steels with finely dispersed particle can be explained by the addition of friction stress and particle dispersion strengthening, in the case the grain size is sufficiently larger than the particle dispersion spacing.

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-SiO 2 -P 2 O 5 ] ternary model sample and Al 2 O 3 and Fe 2 O 3 added therein showed unsaturation with CaO and precipitation of solid 3CaO･P 2 O 5 as the phosphorus-concentrated phase in all the sample.The contamination of the other components in 3CaO･P 2 O 5 was low, especially less than 1 mass% for Al 2 O 3 added samples.The liquid phase was also formed with Al 2 O 3 or Fe 2 O 3 addition, and the liquidus composition in quaternary samples were consistent with those appeared in [CaO-SiO 2 -Fe 2 O 3 ] and [CaO-SiO 2 -Al 2 O 3 ] ternary diagram.P 2 O 5 content in the quaternary liquid…

In order to develop a new recycling process of steelmaking slag, reduction of (FetO) and (P2O5) in steelmaking slag at high temperature has been investigated. In this work, 50 kg-scale experiments which simulated rotary kiln were conducted to investigate the separation behavior between slag and metal. Main results are as follows. (1) Molten iron was tapped out from the experimental furnace under the condition that more than 86% iron was reduced. (2) Weight of reduced iron did not affect the undefined ratio of phosphorus. (3) Common logarithm of phosphorus distribution ratio (logLP), which was used as an index to explain the effect of slag composition, temperature and oxygen potential, correlates to the undefined phosphorus ratio. (4) In the experiments which simulated rotary kiln treatment, calculated phosphorus distribution ratio (LP) was smaller than that from experimental results. It can be said that the phosphorus transfer into the metallic phase decreased because the smaller interface between slag phase and metallic phase was obtained due to the slag/metal separation.

The precipitation behavior of carbides of modified 9Cr-1Mo steel (Grade 91) by low-temperature tempering and the influence of those carbides on the mechanical properties at room temperature were investigated. As-quenched sample (AQ) showed a small amount of MC carbide in the martensite microstructure. Three types of carbides were formed by low-temperature tempering at 300-500ºC that were chosen for the purpose of suppressing recovery and growth of the dislocation substructure. These carbides were identified as Fe4C, hP8 type Fe3C, and oP16 type Fe3C using replica samples for transmission electron microscopic and extracted residue analyses. Double low-temperature tempering at 500ºC for 5 min followed by at 300ºC for 1 h (DLTT) formed a large amount of carbide compared to AQ while AQ and DLTT had similar lath widths. The hardness of the DLTT sample was higher than that of the AQ sample, whereas the tensile strength of the DLTT sample was slightly lower than that of the AQ sample regardless of strain rate. The reason why the precipitation strengthening did not work for the improvement…

In order to investigate the adaptability of small punch (SP) creep testing technique to the remaining-life assessment, the SP creep test was carried out with 2.25Cr-1Mo steel hot rehear steam piping, which had been actually used in a fossil power plant for long periods of time. The SP load (F) was converted to the stress (σ) by three different equations, which were derived based on the displacement to maximum load in the SP test (um) and the deflection to minimum deflection rate in the SP creep test (umin) for correlating the SP creep rupture data with the uniaxial ones. The experimental results showed that the SP creep rupture time of specimen removed at around outer surface of piping tended to be slightly shorter than those taken at around inner surface and center. It was also found that the SP creep rupture data were relatively in good agreement with the uniaxial ones by converting F to σ with the equations, and the creep remaining-life was well predicted by the extrapolation of short-term SP creep rupture data. The highest prediction accuracy was obtained by using the equation…

The partitioning of solute elements during intercritical annealing and the effects of partitioning on ferrite transformation during slow cooling after intercritical annealing in a 0.17% C-1.5% Si-1.7% Mn (mass%) steel were investigated by a new FE-EPMA (field emission electron probe microanalysis) technique. This new technique enables highly accurate measurement of the C distribution. During the intercritical annealing, C and Mn concentrated into austenite, while Si concentrated into ferrite. The distribution of Mn in austenite was inhomogeneous, and austenite with small Mn content was transformed into ferrite during slow cooling. This ferrite transformation proceeded in the NPLE (negligible partitioning local equilibrium) mode. Two kinds of ferrite were produced due to slow cooling, one being intercritically-annealed ferrite, and the other transformed ferrite. The transformed ferrite had larger Mn content than the intercritically-annealed ferrite. Furthermore, the transformed ferrite was classified into the ferrite grown epitaxially from the intercritically-annealed ferrite and…

Sintered ores with superior high-temperature reducibility can enhance indirect reduction at the shaft and permeability at the cohesive zone through improving the softening-melting behavior, resulting in stable operation of the blast furnace at low coke rates.As the depletion of high-grade ore deposits limits control of the chemical composition of sintered ores, small pores less than 10 µm in diameter in the microstructure of sintered ores were focused on to increase the high-temperature reducibility.Sintering conditions for increasing small pores in constant raw material conditions were examined.Furthermore, considering the heterogeneous structure of the sintered ores, reduction behaviors of relict ores and assimilated structures were estimated individually.The contribution of each structure to small pore formation during sintering and their influence on high-temperature reducibility was discussed.Sintering with a sharp temperature profile led to many small pores in the sintered ores by increasing the amount of relict ores with small pores even in constant raw material…