Tribological properties of diamond coatings depend on many parameters, especially on the elaboration process, the coating surface topography, the nature of the counterface and the environment, This paper presents a study concerning diamond coatings, deposited by combustion flame process, rubbing on a HSS steel disc under different environments : air, vacuum, water vapour, oxygen and argon, We applied in our experiments two different normal loads : a high one (1.6 N) to observe the transferred debris, and a lower one (0.37 N) to avoid deep indentation. With a 1.6 N normal load, the friction coefficient increased under oxygen (mu : 0.15-0.18) and water vapour (mu : 0.15-0.20) : that is due to the thickening of the oxide layer. When the normal load is decreased to 0.37 N, the obtained results were similar to the last case, except under water vapour where the friction coefficient increased to 0.25, the influence of the superficial tension forces will be therefore studied. To confirm our conclusions concerning the interactions between diamond and steel, and to highlight the phenomena occurring during the contact, we also present surfaces observations of both pin and disc.