The increasing evolution of dilatometric techniques now allows for the identification of structural transformations with very low signal. The use of dilatometric techniques coupled with more common techniques, such as metallographic, hardness testing, and x-ray diffraction allows to plot a new CCT diagram for AISI M4 high-speed tool steel. This diagram is useful for a better selection of alternate solutions, hardening, and tempering heat treatments. More accurate determination of the various fields of transformation of austenite during its cooling was made. The precipitation of carbides highlighted at high temperature is at the origin of the martrensitic transformation into two stages (splitting phenomena). For slow cooling rates, it was possible to highlight the ferritic, pearlitic, and bainitic transformation.

The present work is to characterize both processes of thermochemical treatments: plasma nitriding and gas. The tests were carried out in collaboration with the Franco-Tunisian heat treatment (F3T) applied to a widely used steel in industrial production as a tool for hot work on X38CrMoV5 (AISI H13). The material underwent a first cycle of hardening heat treatment at 1030℃ followed by two successive incomes at 550℃ and 590℃. After nitriding (ion and gas), the quantification of wear was performed in the laboratory of tribology at SUPMECA (St. Ouen). After defining the test conditions on the alternative tribometer ensuring on one hand a quantitatively sufficient wear and avoiding on the other hand, the phenomenon of jamming. The conditions chosen are: 58.8 N load, frequency 0.5 Hz, friction coefficient μ = 0.5. The wear tracks were scanned using the profilometer Talysurf 5 M type, which allowed us to assess the volume used and the wear rate. Moreover, these tracks were characterized by metallography. What emerges from this work is that the control parameters of ion nitriding ensures a better depth of treatment for the same holding time with a total absence of the white layer known for chipping and fragility

The transformation of iron carbide cementite was investigated on spheroidal graphite containing different contents of manganese. The isothermal maintain were carried out at 600, 650, 700, and 750• C for periods of up to one hour. It was observed that the kinetics of graphitization is slowed even more than cast iron rich in manganese.