Martensitic Transformations of Austenite below 273 K. Dilatometric and Magnetic Studies

Abstract
The transformation of austenite (Fe-C, Fe-1.5Cr-1C, Fe-N, Fe-Mn-N) to martensite during quenching to the ambient temperature followed by cooling to 77 K was studied with a use of dilatometry and magnetic force measurements. We can see three transformations of austenite. The first during quenching, the second during cooling to 77 K, and the third during an increase of temperature from 77 K to the ambient one. The first 40 minutes of holding at ambient temperature influences most significantly the temperature of the second transformation of austenite. Temperatures of austenite transformation indicated as the increase of magnetic force during the third transformation are lower than that determined by increase of volume (dilatometry). Amounts of autenite transformed during the third transformation determined by magnetic force measurements are somewhat higher than those determined by dilatometry. The reasons of these differences are discussed on the basis of recent publications.