The expansion of advanced technologies revealed the importance of diamond coatings in a large range of applications, more particularly for ultra precise - high speed machining. The rising interest for these films had a double repercussion : the diamond deposition methods were developed, and the friction and wear properties of the thus obtained coatings form the subject of many studies. This work is part of this purpose, that is to say the understanding of the tribological behaviour of diamond coatings deposited by flame process, sliding against High Speed Steel discs. Transfer formation and friction mechanisms are studied, according to diamond intrinsic properties and experimental parameters, with the help of Scanning Electron Microscopy observations and Raman spectroscopy analyses. A dynamical pin-disc contact modelling was concurrently realised, by taking into consideration thermal aspect ; the maximum load which can be applied to the couple before the diamond-substrate decohesion can be thus determined.