Nano-Carbides and the Strength of Steels as Assessed by Electrical Resistivity Studies
The work of Frommeyer on electrical conductivity measurements in pearlitic steels is reviewed to provide insight into microstructures developed during wire drawing. Electrical conductivity measurements were made as a function of drawing strain (up to ε = 6.0) for wires with strength exceeding 3500MPa. The results show that electrical conductivity increases during wiredrawing to a maximum value, then decreases with further deformation finally reaching a steady state value that is equal to the original conductivity. The initial increase is the result of pearlite plate orientation in the direction of wire-drawing, which makes the path of conduction through the ferrite plates more accessible. At a critical strain the cementite plates begin to fragment and the electrical conductivity decreases to a steady state value that is the same as that observed prior to wire drawing. With increasing strain, the cementite particles are refined and the strength increases due to the reduction in inter-particle spacing. It is concluded that the electrical conductivity of the wires is solely dependent on the amount of iron carbides provided they are randomly distributed as plates or as particles. An estimate was made that indicates the carbide particle size is approximately 3 - 5 nm in the steady state range of electrical conductivity.
T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran
D.R. Lesuer et al., "Nano-Carbides and the Strength of Steels as Assessed by Electrical Resistivity Studies", Materials Science Forum, Vols. 539-543, pp. 4789-4794, 2007