A study of the alpha <->gamma transformation in pure iron: rate variations revealed by means of thermal analysis

作者：Papandrea C; Battezzati L^*

来源：Philosophical Magazine, 2007, 87(10): 1601-1618.

DOI：10.1080/1476430601080260

The alpha <-> gamma transformation in nominally high purity Fe is shown to Occur with a stepped peak in differential thermal analysis on both heating and cooling at rates between 0.5 K min(-1) and 10 K min(-1). The composite peaks mark changes in the transformation rate. To endorse the findings, the instrumental output has been thoroughly analyzed providing evaluations of time lags, suggestions for calibration and for the use of the derivative of the peak. The change in rate occurred in all samples irrespective of their grain size (average values from 91 mu m to 1100 mu m). The rate of movement of the interface in the alpha <-> gamma transformation is estimated between 4 x 10(-5) ms(-1) and 3 x 10(-6) ms(-1). The present results extend previous dilatometric work in which the rate variation was detected only for large grain size and low undercooling. Possible reasons for the variation in rate are outlined: local development of strain in the austenite due to lattice misfit with respect of the growing ferrite, formation of a ragged microstructure and pinning of the boundaries by impurity.

• 出版日期2007-4-1