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

Electrical resistivity of low-carbon martensitic steels was measured to estimate the carbon concentration in solid solution. Since electrical resistivity is influenced not only by solute carbon but also by substitutional elements, lattice defects and second phase, the effects of these factors need to be subtracted from total electrical resistivity, in order to obtain the accurate solute carbon concentration by this method. As a result, the effects of dislocations and grain boundaries were much smaller than that of solute elements, being only 1 - 2% of the measured electrical resistivity, in martensitic steel. On the other hand, substitutional elements and retained austenite were found to be significantly effective. By subtracting these effects from the measured value, the change in electrical resistivity due to solute carbon, Delta(rho sol.C), could be formulated as a function of the carbon concentration in solid solution of martensite, C-s(ol), as follows: Delta(rho sol.C) [m Omega mm] = 0.25 x C-sol [mass%] The estimated solute carbon concentration was confirmed to correspond to the directly measured value by atom probe tomography.