Estimation of Solute Carbon Concentration by Electrical Resistivity Measurement in Martensitic Steel

Quantitative Analysis of Hardening Due to Carbon in Solid Solution in Martensitic Steels

“…In previous study, 5,18) we confirmed that an effect of segregated C into dislocations and grain boundaries on electrical resistivity could be negligible. Each factor was estimated as follows: 5,26,27) ∆ Ω ρ sub m mm M n mass .…”

“…Subsequently, the average value was calculated from 10 points, excluding the maximum and minimum values. It is empirically known that there is a proportional relationship between Vickers hardness (H v ) and tensile strength (σ) in C steels; 24,25) The solute C concentration (C sol ) of the specimens was estimated through electrical resistivity measurements using the four-point method at 77 K. 5,18) The specimens for electrical resistivity measurements were prepared by first cutting to square bars of 1 mm × 1 mm × 50 mm and then wet-polishing the bars with emery polishing papers. After the specimens were held in liquid nitrogen for 60 s, the electrical resistivities were measured twice while changing the current direction, and the average value was calculated.…”

“…Therefore, by performing measurements in liquid nitrogen, the effect of ρ L became approximately zero. We previously reported that C sol in martensite is as follows: 5,18)…”

“…In addition, more phenomena occur during tempering, such as a decrease in supersaturated solute C, 4,5) precipitation of C-clusters and metastable carbides, 6,7) decomposition of retained austenite, 8) transition and Ostwald ripening of carbides, 9,10) decrease in dislocation density, 11) and formation of subgrains 12) with recovery. Therefore, a quantitative evaluation of the strengthening mechanism of tempered martensitic steels by separating their effects on strength is challenging.…”

“…17) Thus, APT is not always appropriate as a method of measurement for solute C concentration to relate it with macrohardness in martensite. In contrast, Masumura et al 5,18) suggested a method for evaluating the solute C concentration in martensitic C steels through electrical resistivity measurements. Subsequently, macroaverage information of the amount of solute C concentration can be estimated using this method.…”