3. Highlighting the metallurgical mechanisms at work during extensive tempering of carbonitrided structural steels

To understand the evolution of the metallurgical mechanisms at work during advanced tempering, we can either use transmission electron microscopy to observe the evolution of the phases present, or look at quantities resulting from the metallurgical structure, such as micro-hardness and residual stresses, for which it is necessary to estimate the content of the main phases present. This second approach has been favoured in this chapter; nevertheless, the conclusions drawn are in line with the structural approach developed by the University of Lorraine.