Changes in Thermoelectric Power and Electrical Resistivity in the Processes of Cold Rolling and Isochronal Annealing in Pure Iron

Abstract

Changes in thermoelectric power, electrical resistivity and Vickers hardness in the processes of cold rolling and isochronal annealing at 30 min/20°C step were observed in J. M. pure iron and electrolytic iron decarburized and denitrided. The cold rolling and isochronal annealing processes could be separated into different regions by plotting the observed values on absolute thermoelectric power (S_0°C) -conductivity (1/ρ_0°C) diagrams.
From the S_0°C-1/ρ_0°C diagram for J. M. pure iron, the average gradient of the lines corresponding to increase and decrease of dislocation density was found to be 500±100 μV·μΩ·cm/deg. The cold rolling process in electrolytic iron could be separated into three regions. The 1 st region which was confined within about 10% reduction was considered to be influenced by segregation of nitrogen and carbon atoms onto dislocations. The onset of 3rd region above 40% reduction was explained as due to vacancy formation. On annealing over 500°C, dissolution of nitrogen and carbon atoms took place in both the specimens, and the gradient of the lines on S_0°C-1/ρ_0°C diagram was 130±50 μV·μΩ·cm/deg.