A new numerical method to analyze reaction and heat transfer in layered packed bed of layered burden materials was developed. This method combines steady-state simulator of blast furnace operation and “digital basket” model. The digital basket is a fixed bed of burden materials through which the reducing gas flows. The fixed bed can be a mixture or layers of iron ore and coke. The mathematical expression for the digital basket is a subset of blast furnace simulator which consists of one-dimensional conservation equations of mass, heat and chemical species, and rate equations of reactions and heat exchange for gas and burden phases. The reducing gas temperature, composition and flow rate are used as the boundary condition at the bottom of the digital basked. These variables are extracted along a trajectory of descending burden material that is estimated by the blast furnace simulator. This treatment combines the blast furnace simulator and the digital basket model, and allows to reproduce the reaction and heat transfer behaviors of the burden bed descending in the blast furnace. This new method was applied to mixed and layered packed bed of iron ore and coke and successfully revealed the differences in the processes of heating and reduction reaction. The results showed that the deviations of the gas and solid compositions in the burden layer were enlarged under the mixed charging condition compared to the mixed charging. This is due to the separate occurrence of the reduction reaction and the coke gasification.

With the increasing strength requirements for automotive spring steels, hydrogen embrittlement has become a critical issue.

The precipitation of fine ε-carbides has been identified as an effective method in mitigating hydrogen embrittlement. However, precise quantitative evaluation of their size and volume remains essential for effective microstructural control.

In the present study, ε-carbides in spring steel were quantitatively analyzed using small-angle X-ray scattering (SAXS), and the reliability of the results was evaluated. The volume fraction determined by SAXS was compared with the maximum precipitation calculated from solute carbon content, while particle size was assessed based on transmission electron microscopy (TEM) observations.

Specimens of SAE9254 steel were quenched at 950°C and subsequently tempered between 150°C and 450°C. Conventional SAXS analysis, which assumes a single-component fitting, yielded volume fractions that exceeded the calculated maximum. In contrast, the application of a two-component fitting approach, which accounts for scattering contributions from both the martensitic matrix and ε-carbides, produced results consistent with the calculated maximum.

Discrepancies were observed between particle sizes measured by SAXS and TEM, with the divergence increasing at higher tempering temperatures. This discrepancy is primarily attributed to the difficulty in detecting smaller particles using TEM, particularly when the precipitates exhibit a broad size distribution.

These findings confirm the effectiveness of the two-component fitting method and demonstrate enhanced analytical accuracy in the quantitative evaluation of ε-carbides using SAXS.

Steelmaking slag, a by-product of the steelmaking process, contains free CaO (f-CaO), which hydrates to form Ca(OH)₂, causing significant volume expansion and disintegration. Basic Oxygen Furnace (BOF) slag with its high f-CaO content exhibits particularly severe expansion. At JFE Steel, steelmaking slag intended for use as subbase course material is treated in a steam aging facility to stabilize expansion and slag expansion after aging is evaluated using the expansion stability test specified in the JIS standard. However, nonuniform steam distribution during aging often prolongs stabilization and increases steam consumption. In addition, some aged slags are not sufficiently stabilized and fail to meet the criteria, requiring re-aging and reducing productivity. This study aims to investigate the mechanisms and causes of delayed temperature rise and steam flow heterogeneity in steam aging facilities. Steam flow heterogeneity was analyzed through laboratory-scale experiments, on-site sampling, and numerical simulations based on actual slag properties. The results revealed that the steam flow heterogeneity arises from ruts formed by heavy machinery and particle size segregation during the slag piling process, with ruts having a greater influence than segregation. These findings indicate that optimizing piling methods is essential for improving steam distribution, reducing energy consumption, and enhancing productivity in steam aging facilities