Establishing of Rolling-Friction Coeffocient, for Hertzian Contacts Between Steel Balls and Different Kinds of Thermochemical Treated Steel Surfaces

Abstract

It is known that for the ball displacement guide paths, the necessary startmoving force of the mobile half-couple is higher than the displacement-motion keeps force.Within the frame of this work, it has been designed and manufactured special pairs of rolling-motion couples, made from 5115AISI case-hardening steel and 4140 AISI heat treatable steel. After that, some of them (in the first blend) were carburized (at 925oC) and others carbonitrided (at 890oC) in gaseous conditions. The rolling - friction tests supposed different arrangements of the half-couples and balls. In order to establish the rolling - friction coefficients for all the thermochemical treated surfaces, a typical method such as the inclined plane slope, was used. Taking into account each kind of superficial treatment category, generally, it has been observed smaller values of equivalent friction coefficient for the carburized surfaces in comparison with the carbonitrided ones. For low - temperature superficial treatments category, a little bit smaller values of equivalent friction coefficient for the nitocarburized surfaces in comparison with the nitrided ones were obtained. The non-treated surfaces have been characterized, in all the cases, by minimum friction coefficient values in comparison with the treated ones. In comparison, the results clearly show a difference between the equivalent friction coefficient values registered for carburized/carbonitrided and nitrided/nitrocarburized surfaces. Thus, in the first case, these values were smaller than in the second case.