The effect of some methods of surface treatment on fatigue strength under the fretting conditions was investigated in EA1N normalized carbon steel with 0,4% C and in EA4T quenched and tempered low alloy CrMo steel. There were applied surfacing methods creating favorable compressive stresses in surface layer and, in some cases, an increased hardness of surface. To obtain data on the effect of work-hardened surface by shot peening, ion-nitriding and ion-carbonitriding on the life-time of fretting fatigue loaded parts, specially instrumented fatigue tests under conditions of fluctuating loading with fretting were performed. The procedures of surfacing as well as typical parameters characterizing the surface layers are described in detail. Fatigue limits relating to 10(7) cycles were evaluated from the fatigue curves. The results of fatigue tests of surface treated bars are compared with those obtained on bars without surfacing. Applied types of surfacing had an important - and mostly very favorable - effect on the fatigue strength under conditions of fretting. The extent of favorable effect in ion-nitrided and carbonitrided bars depended on the type of the base material as well as on the hardness and chemical composition of surface layers. In some cases, the unfavorable effect of fretting on the fatigue strength was almost completely suppressed. The increase of hardness in surface layer influenced favorably the conditions of seizing and roughening in the contact areas. Compressive residual stresses in surface layers also played an important role as they caused the retardation of nucleation and growth of fretting cracks and, in this way, they contributed to prolongation of the fatigue life-time.
