The 10 most-cited articles in 鐵と鋼 : 日本鐡鋼協會々誌, 2022

To clarify the effect of alloying elements (M) on the grain boundary segregation behavior of boron (B) and carbon (C) in α-iron, the grain boundary segregation of B, C and alloying elements was evaluated thermodynamically for the Fe–B–1.0 at.%M and the Fe–C–1.0 at.%M ternary systems (M: Al, Ti, V, Cr, Mn, Nb, Mo) using the parallel tangent law proposed by Hillert. In this calculation, the Gibbs energies of the liquid phase in the Fe–B–M and Fe–C–M ternary systems were applied to those of the grain boundaries. According to the calculated results, in the Fe–B–M ternary systems, co-segregation of Ti, V, Mn or Nb with B was predicted, while no co-segregation behavior was confirmed in the case of Al, Cr or Mo addition; in the Fe–C–M ternary systems, co-segregation of Ti, V, Nb or Mo with C was predicted, while no co-segregation behavior was confirmed in the case of Al, Cr or Mn addition. These co-segregation tendencies correspond well with the formation tendencies of metal borides or metal carbides. Although the present calculated results were based on the assumption that substitutional…

Since 10 million tons of steelmaking slag, which contains a few percent of phosphorus, are annually produced, the phosphorus amount in the slag is equivalent to the annual import volume of phosphorus rock in Japan. Therefore, the steelmaking slag is attracting attention as a potential phosphorus resources. Phosphorus-concentrated slag obtained by the dephosphorization reaction between high phosphorus hot metal and oxidizing slag at high temperature contains phosphorous comparable to that of phosphorus rock. However, because of high FeO concentration, it is difficult to use for phosphorus resources directly. In this work, the effects of pH, acid type and leaching method on the dissolution behavior of phosphorus from P-concentrated slag were investigated. As a result, phosphorus dissolution progressed at lower pH, and was promoted by the addition of citric acid, which is known as a chelate former. When nylon mill pot stirring with citric acid and alumina mill pot stirring with nitric acid were compared to impeller stirring, respectively. By combining nylon mill pot stirring and…

Zn–Ni alloys were electrodeposited on a Cu electrode at 10–5000 A·m−2 and 5 × 104 C·m−2 in an unagitated zincate solution at 293, 313, and 333 K. The effect of solution temperature on the electrodeposition behavior of Zn–Ni alloys from alkaline zincate solutions was investigated. The transition current density at which the deposition behavior shifted from a normal to anomalous codeposition was almost similar at 293 and 313 K but increased at 333 K. The transition current density increased at 333 K due to the enhanced hydrogen evolution and Ni deposition. The current efficiency for alloy deposition increased with solution temperature in both normal (10–50 A·m−2) and anomalous (500 A·m−2) codepositions region. In a normal codeposition region, Ni deposition and hydrogen evolution mainly occurred, and the current efficiency increased with solution temperature due to a larger promotion effect of increase in solution temperature on the Ni deposition. In an anomalous codeposition region at 500 A·m−2, Zn deposition and hydrogen evolution mainly occurred, and Zn seems to proceed under a…

Novel oxide particles composed of Ti, rare-earth metal and Zr was found by the present authors to promote the formation of acicular ferrite (AF), but their effect on toughness has not yet been clarified. Therefore, influence of AF formation on toughness of low carbon steel has been investigated using Ti-Rare earth metal-Zr-killed (TRZ) steel and Al-killed (AL) steels in this study. Dominant microstructure of the AL steel is bainite forming block/packet structure elongated from prior austenite grain boundaries. In contrast, a large amount of AF which grows from intragranular inclusions is formed in the TRZ steel. Toughness of the TRZ steel is better than the AL steel. In addition, at higher austenitizing temperature, AF formation is promoted in the TRZ steel, leading to lowering ductile-brittle transition temperature. Cracks in Charpy impact specimens propagate along {001}α plane and deflect at Bain unit boundary across which {001}α planes are largely misoriented, which means the effective grain size for crack propagation is Bain unit size. Bain unit size is smaller in the TRZ steel…

Commonly, plain carbon fresh martensitic steel shows high strength and breaking immediately. However, low C–2 wt.%Si–5 wt.%Mn fresh martensitic steel exhibits excellent strength and ductility. But it's not clear why 5 wt.%Mn martensitic steel has ductility more than plain carbon martensitic steel. In this study, the effect of C and Mn on strength and ductility is investigated by in-situ X-ray diffraction during tensile tests in SPring-8. The relationship between the work hardening behavior and the dislocation behavior is analyzed. The dislocation density was calculated with modified Williamson-Hall method and modified Warren-Averbach method. XAFS measurement was also performed to investigate the interaction between Mn and C. It was found that the increase rate of dislocation density in plain carbon martensitic steel was higher than in 5%Mn martensitic steel. Adding 5%Mn, the increase rate of dislocation density can be reduced. We found that the tensile strength is determined by the upper limit of dislocation density, and the uniform ductility is determined by the increase rate of…

Forming simulation is an indispensable analysis tool in industry. The most important thing in forming simulation is to reproduce the deformation behavior of the material during forming as accurately as possible. This paper reviews various material test methods developed from the viewpoint of improving the accuracy of material models for sheet metals, and the deformation characteristics and material modeling of steel sheets. Section 2 describes the difference between the yield surface and the contour of plastic work to explain the advantages of constructing a material model based on the latter. Section 3 gives an overview of various material test methods for measuring the contour of plastic work of sheet metals. Sections 4 and 5 show examples of measuring the deformation behavior of steel sheets in linear and nonlinear stress paths, and related literature.

We have attempted to predict creep rupture time for a wide range of ferritic heat resistant steels with machine learning methods using the NIMS Creep Data Sheet (CDS). The dataset consisted of commercial steel data from 27 sheets in the CDS, covering various grades of carbon steels, low alloy steels, and high Cr steels. The prediction models were constructed using three methods, support vector regression (SVR), random forest, and gradient tree boosting with 5132 training data in order to predict log rupture time from chemical composition (19 elements), test temperature, and stress. Evaluation with 451 test data proved that all three models exhibited high predictivity of creep rupture time; in particular, the performance of the SVR model was the highest with a root mean squared error as low as 0.14 over the log rupture time, which value means that, on average, the prediction error was factor 1.38 (=100.14). The high predictivity achieved with no use of information on microstructure was presumably because the data used was for commercial steels in which there should be a correlation…

To evaluate the susceptibility of steels to hydrogen embrittlement, it must be hydrogen charged and have its hydrogen content controlled before any mechanical testing. In this study, hydrogen permeation tests of an iron sheet were performed during potentiostatic hydrogen charging in various solutions containing ammonium thiocyanate to obtain a guideline for efficient hydrogen charging for a wide range of hydrogen contents. As the polarization potential shifted in the negative direction, the hydrogen permeation current increased before becoming almost constant. In all cases, besides when an aqueous sodium hydroxide solution was employed, the hydrogen permeation current increased due to the addition of ammonium thiocyanate. The effect of adding ammonium thiocyanate was enhanced as the aqueous solution pH was decreased. The hydrogen permeation current under various hydrogen charging conditions obtained in this study can be used as a reference for hydrogen charging of steels.

Life cycle assessment (LCA) has been developed for evaluating the environmental impacts associated with a product through its life cycle. LCA is used in product environmental footprint programs. In carbon neutrality, greenhouse gas emissions associated with a product and an organization are of great interest, where methodologies and databases developed for LCA are used. Thus, LCA has become an essential tool for the zero-emission society and circular economy. However, when LCA is applied to materials, a material life cycle may contain several product life cycles due to its recycling. Therefore, evaluation methodologies for consuming secondary raw materials and for recovering them should be seriously considered. This article provides basic knowledge of LCA and advanced knowledge for recycling effects. As basic knowledge, the difference between attributional LCA and consequential LCA and their selection depending on the purpose of assessment are described. As for the recycling effects, characteristics of three possible modeling approaches, cut-off, portioning, and avoided burden…

A selective oxidation of alloying elements such as Si and Mn is generally important for the zinc wettability of high strength steels in the process of hot dip galvanizing. In the present paper, the effect of both the temperature and the dew point of recrystallization annealing process on the selective surface oxidation behavior of 2 mass% Mn added steel were investigated by glow discharged spectroscopy (GD-OES), secondary electron microscopy (SEM) and transmission electron microscopy (TEM). When the annealing temperature was below 973 K, the Mn internal oxidation did not occur and the amount of Mn external oxidation increased with increasing temperature regardless of the dew point. On the other hand, when the annealing temperature was more than 1023 K, both the external oxidation and the internal oxidation were observed. Especially, the internal oxidation occurred actively and the external oxidation is suppressed when the dew point is more than 263 K. Wagner’s theory could explain the phenomenon which the internal oxidation was occurred in the wider range of dew point as the…