Differential resistivity as a means of monitoring annealing in steels

Annealing of cold-worked plain carbon and high-strength low-alloy steels may be monitored in situ by measurement of differential electrical resistivity using an alternating current method. The change in room-temperature resistivity is about 4% for steels given a prior cold reduction of 80%. Recovery and recrystallization are distinguishable as two separate stages in these materials; the onset and end point of recrystallization can be identified during the progress of annealing. It was also possible to observe changes in resistivity resulting from grain growth. However, the changes could not be quantified since grain-growth rates were extremely slow in the steels studied.