Roughness characterizes the quality of the machined surfaces, mainly determined by the geometric tolerances and induced by the different factors involved in the cutting process. The aim of this paper is to study the influence of cutting parameters (cutting speed (Vc), feed rate (f), tool nose radius (Rc) and cutting depth (ap)), on the cylinder surface roughness, in order to value the friction coefficient (μ) and the wear rate (W) of the contact surfaces of steel-steel pair: 42CrMo4-20MnCr5. Full factorial design (DOE) of 9 tests is used, to develop theoretical model of the roughness of machined metal parts on turning. Hence, the influence of the cylinder roughness on the friction and wear behavior of the steel-steel pair contact  is studied, using a pin-cylinder tribometer. The results revealed that the friction coefficient and wear rate, increases progressively by varying the surface roughness (cutting parameters). The processing and observations of the results were recorded using a profilometer, an optical microscope, a scanning electron microscopy (SEM) followed by an analysis in energy dispersive spectroscopy (EDS). However, the surface of the pin is plowed, cracked and plastically deformed, thus inducing more loss of material by adhesion and oxidation of the formed particles on the cylinder, which bring about a material transfer and formation of a metal oxide layer.