Electrical resistivity changes of water-atomized unreduced steel powder compacts during sintering process were measured and compared with the dilatometric changes. Release of gases from powders during heating in vacuum was also studied in connection with reduction of oxide films on the particle surfaces.
The results obtained are as follows:
(1) The electrical resistivity of unreduced powder compacts changes drastically during heating from room temperature to about 600°C. Especially an anomalous change in resistivity is observed between 300 and 400°C in coincidence with active release of gases due to the decomposition of goethite on the particle surfaces.
(2) The reduction of oxide films on the particle surfaces occures mainly in the temperature range 800-900°C showing the maxium of resistivity.
(3) The α↔γ transformation is not observed in the resistivity measurements, while it is observed clearly in the dilatometric measurements.