The 10 most-cited articles in 鐵と鋼 : 日本鐡鋼協會々誌, 2023

Materials Integration is the concept of accelerating materials development by linking processing, structure, property, and performance (PSPP) on a computer using any types of models such as theoretical, empirical, numerical-simulation, and machine learning models. In the first and second phases of Cross-ministerial Strategic Innovation Promotion Program in Cabinet Office, Japan, we have developed a system called MInt (Materials Integration for Network Technology), which links PSPP with computational workflows that combine modules implemented, in order to realize the concept of Materials Integration. MInt is equipped with an application programming interface (API) that can be called from various algorithms in the artificial intelligence (AI) field and one can use MInt-API together with the AI algorithms to inversely design materials and processes from desired performance. The target material systems have expanded to steel, aluminum alloys, nickel alloys, and titanium alloys, and the target processes have also expanded to welding, heat treatment, 3D additive manufacturing, and powder…

The effects of C and N on solid solution strengthening and grain refinement strengthening were quantitatively evaluated using various austenitic stainless steels in which C and N were added independently to Fe-18 mass%Cr-12 mass%Ni alloys. As a result of evaluating the amount of solid solution strengthening from the intercept value in the Hall-Petch relationship, it was confirmed that N has a stronger solid solution strengthening capacity than C. On the other hand, the addition of C and N increased the slope of the Hall-Petch relationship, the so-called Hall-Petch coefficient, and the amount of grain refinement strengthening increased. Comparing the effects of C and N, there was no significant difference in the effect of increasing the Hall-Petch coefficient between the two elements at the same amount of addition. The critical grain boundary shear stress measured by nanoindentation tests and the Hall-Petch coefficient corresponded well for both steels, demonstrating that the increase in critical shear stress due to the addition of C and N results in increased grain refinement…

The microstructure of the B1-type TiC formed during solidification and its mechanical properties were investigated using arc-melted Fe-Ti-C ternary alloys. The TiC formed at relatively high temperatures in the liquid as the primary phase exhibited a dendritic shape. With decreasing temperature and/or decreasing Ti and C content in the liquid, its morphology changed to a cubic shape with the {001}TiC habit plane, a plate shape with the {011}TiC habit plane, and a needle shape with the <001>TiC preferential growth direction. The morphology of the TiC was characterized by the anisotropy of its surface energy and its growth rate. The cubic shape with the {001}TiC habit plane was formed as a result of the minimum surface energy of the {001}TiC. However, the plate shape with the {011}TiC habit plane and the needle shape with the <001>TiC preferential growth direction should be formed due to the slowest growth rate of <011>TiC and the fastest growth rate of <001>TiC, respectively. At room temperature, alloy with the dendritic TiC was fractured in the elastic deformation region because the…

The skidding between rolls and steel strip is more likely to occur in the cold rolling process in accordance with an increase of tensile strength of the material following the customers' demands. This happens when the work rolls rotates faster than the longitudinal speed of the strip at the exit of the roll-bite. This phenomenon leads to not only the strip surface defection but the thickness nonuniformity and thus the aim of this study is defined to clarify the mechanism behind the phenomenon. In order to clarify the factor causing the skidding, the cold rolling experiments using two different steel grades, namely the Low Carbon Steel (LCS) and the Advanced High Strength Steel (AHSS) having respectively 270 and 980 MPa tensile strength, have been conducted, which was then assessed by the numerical analyses and the comparison of the forward slip characteristics was made between these two steel grades. It has been revealed that the forward slip is decreased under the low friction coefficient condition with an increase of the rolling reduction. In addition, the friction coefficient of…

The effect of dislocation density on hydrogen embrittlement resistance of tempered martensite in low alloy steels was investigated quantitatively. The various samples of which dislocation density was from 0.7×1014 m−2 to 4.5×1014 m−2 were prepared by changing tempering temperature and C content. Then, the yield stress of the samples was between 780 MPa and 1020 MPa. Especially, the change of the C content made various dislocation density samples even though the yield stress is almost same. The hydrogen embrittlement resistance was estimated with four-point bend test. The hydrogen embrittlement resistance decreases with increasing the dislocation density and the yield stress. Although the critical yield stress was changed dramatically by changing C content, the critical dislocation density was almost same (about 2.0×1014 m−2) even though the C content was different. In addition, the absorbed hydrogen content correlated with the dislocation density, and did not depend on the C content in this research. This means that the dislocation density is higher, the hydrogen trapping ability is…

We analyzed the crystal orientation of pure iron with two-way cold-rolling and subsequent annealing. As-received pure iron sheets were cold-rolled in the vertical direction against the cold-rolling direction of the as-received sheet, and then in the cold-rolling direction of the as-received sheet. The cold-rolled specimens were annealed in two conditions (short-term and long-term annealing). As short-term annealing, cold-rolled specimen was heated to desired temperature, and then water-quenched to room temperature (298 ± 2 K). As long-term annealing, cold-rolled specimen was heated to 1123 K and held for up to 180 min, and then furnace-cooled for up to 150 min and water-quenched to room temperature. The strain distribution of cold-rolled specimen was uniform, and Goss orientation grains were observed at the interface of α-fiber and γ-fiber and within the micro-shear bands in γ-fiber. By short-term annealing, Goss orientation grains within micro-shear bands grew, whereas those at the interface of α-fiber and γ-fiber disappeared. Abnormal grain growth of Goss orientation grains was…

In the process of steelmaking refining, slag used in the preliminary treatment of molten iron or the converter is a multiphase melt. It contains solid particles that cannot dissolve entirely from the raw materials and gas bubbles generated through reactions, thus making it a multiphase molten material with dispersed components. The flow characteristics of the suspensions, foams, and emulsions significantly affect the separation of iron particles in the slag and the behavior of slag discharge. Multiphase melts typically behave as non-Newtonian fluids, so the evaluation, focusing on viscosity, is crucial to understanding their flow characteristics. This report reviews recent advances in slag visualization techniques for understanding the flow of multiphase molten materials. The results are as follows:

Studies on the oxide scale in hot-rolling process are reviewed. This paper outlines scale formation and the effects of alloying elements on scale formation, scale behaviour in hot-rolling processes such as rolling and descaling, blistering phenomenon, red scale, whisker generation, scale transformation, and Cu-induced hot shortness.

Slag foaming is a phenomenon caused by the generation of CO bubbles due to the reaction between iron oxide in slag and carbon in pig iron. The purpose of this study is to explore the controlling factors of slag foaming by observing the bubble formation behavior caused by the chemical reaction between iron oxide and Fe-C alloy in slag. 0.06 g of Fe-C alloy was charged to the bottom of the BN crucible, and 6.0 g of slag (SiO2:CaO:Fe2O3 = 40:40:30) was charged on top of it. The crucible was placed in an infrared image heating furnace, and the temperature was rapidly raised to 1370°C at a rate of 1000°C/min in a N2 stream, then held for a predetermined time and rapidly cooled. After rapidly cooling, the internal structure of the sample was observed using a high-resolution X-ray CT device. The spherical equivalent volume is calculated based on the number of bubbles observed and their equivalent circle diameter, and the relationship between the volume ratio of small bubbles in the slag volume and the distance from the bottom of the crucible is calculated, and the bubble density and volume…

A novel solid-state joining method called Cold Spot Joining (CSJ) has been successfully developed. In this joining concept, the material near the joining interface is plastically deformed under high pressure to form a joining interface, resulting in the fragmentation of oxide films at the joining interface and the formation of strong interface. Medium carbon steel sheets were CS-joined under various process conditions. The joining temperature can be varied by the applied pressure during CSJ. Microstructural observations and hardness distribution indicated that the appropriate pressurization resulted in joining temperatures below the A1 point and suppressed the formation of the brittle martensitic structure. By providing appropriate applied pressure, sound S45C spot-welded joints were successfully produced, showing plug failure of the base metal in both tensile shear and cross-tension tests. Further investigation into the mechanism of interface formation reveals that the oxide film at the interface is fragmented and expelled. At the same time, dynamic recrystallization occurs at the…