The effect of ball hardness on four-ball wear test results

The hardness of mating surfaces is an important component of the so-called friction parameters vector and has a significant influence on the magnitude of the friction and on the wear of the surfaces. Investigations aimed at determining the influence of hardness on the wear of machine parts working in mixed lubrication range were carried out using a four-ball extreme pressure tester. The test balls were made of 100Cr6 steel with a hardness of 24–62 HRC. A mixed lubrication model (an objective function) correlating the hardness of the steel sliding surfaces, the magnitude of the friction and the wear of the surfaces in a defined area of excitations (pressure pH and sliding velocity vv) for lubrication with oil Transol 150 has been developed. Hardness has been found to have a significant influence on wear. Thanks to the correlation of hardness with the excitations it has been observed that the objective function d = f(pH, vv, H) is not a monotone function, but it has an extremum. The model allows one to match steel materials for sliding nodes working under concentrated contact (e.g. in gears) without the need to carry out experimental tests.