Electrical resistivity measurement is a powerful method for evaluating the solute carbon concentration (C_sol) in BCC iron. In this study, the effect of carbide precipitation on the accuracy of C_sol quantification was examined by applying a model that predicts the electrical resistivity of composite microstructures containing dilute-dispersed spherical carbides. For Fe–C alloys with spheroidized cementite dispersed in ferrite, C_sol in ferrite could be estimated with an uncertainty of only several tens of ppm. In Fe–0.2Mn–C alloys, high accuracy comparable to that of Fe–C alloys was achieved when Mn enrichment in ferrite accompanying cementite precipitation was properly taken into account. For Fe–2Mn–0.5Si–C martensitic alloys, Mn partitioning, dislocation annihilation, and grain coarsening do not occur during tempering at low-temperature below 573 K. Therefore, changes in electrical resistivity during tempering directly reflected the decrease in C_sol, enabling accurate evaluation when the contribution of carbide precipitation was removed using the spherical dilute-dispersion model. In contrast, high-temperature tempering at 873 K induced pronounced Mn partitioning, and even slight uncertainties in the measured Mn concentration in ferrite led to errors of several hundred ppm in the estimated C_sol. Although errors associated with volume fraction and electrical resistivity of carbides also affected the evaluation, their impact was much smaller than that of Mn partitioning. Consequently, except for the high-temperature-tempered Fe–2Mn–0.5Si–C alloy, the final accuracy of C_sol measurement can be maintained within several tens of ppm when appropriate corrections are applied.

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.