Estimation of Solute Carbon Concentration by Electrical Resistivity Method in Low-Carbon Martensitic Steel

The concentration of solute carbon in as-quenched tempered low-carbon martensitic steels (Fe-2%Mn-0.3%C) were estimated from the electrical resistivity. It was found that the electrical resistivity decreased gradually with the increase of the tempering period, and its decreasing rate was enlarged by raising the tempering temperature. The decrement in electrical resistivity was mainly due to the decrease in the amount of solute carbon caused by carbide precipitation. An empirical equation was then applied to convert the electrical resistivity to the solute carbon concentration, where the densities of dislocation and that of grain boundary were also taken into account. Quantitative analysis for a specimen tempered at 373 K for 3.0 ks revealed that the concentration of solute carbon was decreased by 0.005 mass% during the tempering. This estimated value agreed well with the amount of precipitated carbide (Fe_2.5C) measured by TEM observation. As a result, it was concluded that the solute carbon concentration could be estimated quantitatively from the electrical resistivity measurement in as-quenched and tempered martensitic steel.