Evaluation of the electrical resistivity of steels

Abstract

Literature data on the physical properties of steels have been collected and put into a database. The resistivity of steels has been analyzed as a function of composition and microstructure. An overview over former studies is given. The steels have been investigated in two groups, ferritic steels and austenitic steels. A thermodynamic analysis with ThermoCalc has been performed. Regression analysis on the influence of composition on the resistivity was then carried out. The results for ferritic steels are: Si and Al have the highest elemental resistivity, followed by Mn, Cu, Ni, Mo, and Cr. C precipitated in cementite shows a high coefficient in the analysis when the amount of Fe bound in cementite is not considered separately. C in solution with ferrite shows no significant effect. Cr bound in cementite shows a significant effect but Mn, though present in cementite in comparable amounts, has no significant effect on the resistivity. N and C have the highest elemental resistivity in austenite, followed by the substitutional solutes Nb, Si, Ti, Cu, Ni, Mo, and Cr. The carbides NbC and TiC appear with a higher coefficient in the regression model than can be explained by phase-mixture models providing upper and lower bounds for the resistivity of two-phase alloys. Cr23C6 shows no significant effect. The regression results can be used to predict the resistivity of steels with known composition. The model predicts the resistivity of ferritic steels with a maximum deviation between experimental and computed value of 12 nΩm and a standard deviation of 5.6 nΩm. For austenitic steels, the model prediction shows a maximum deviation of 52 μΩcm and a standard deviation of 20 nΩm.