Phase Transformations in Iron-Based Interstitial Martensites

摘要

The present work demonstrates that by combining several experimental methods, as diffraction, dilatometry and calorimetry, new insights are obtained on the phase transformations of iron-based martensites. On tempering martensite a series of consecutive, more or less overlapping phase transformations takes place. Then, for studying the kinetics of such processes, nonisothermal experiments, instead of isothermal experiments, can be useful: the range of temperatures accessible for isothermal analysis of a single transformation can be too narrow for sufficiently accurate interpretation, whereas nonisothermal analysis can be well possible, because the range of heating rates can be less restricted by overlap with previous and next transformations. The approach has been shown to be very useful for studing the kinetics of tempering of martensites (chapters III.2, III.3 and IV). The method employed is derived and discussed in chapters III.1 and III.2. Very little attention has been paid to structural changes on tempering of ternary FeCN martensites until now. Experimental results on the tempering of FeCN martensites are presented in chapter V. They lead to a novel proposal for the tempering sequence of FeCN martensites.