The analysis of a large range of sintered parts shows the fact, they are strained at contact fatigue, in most of the cases. The Hertzian pressure, at which materials in contact are subjected, establishes the appearance of variable stress, which records a maximum at some depth under the contact surface. In the case of sintered materials this stress variation conducts to a faster degradation of strained surface than in the case of compact materials. This is because the stress variation establishes a critical state at the level of stress concentrators, generated by pores, standing in material structure, leading to formation of some cracks which may propagate at the level intergranular necks, producing removal for some particles of material. The accomplished research on sintered materials, having different chemical compositions, revealed the fact, at the beginning, that the materials undergo a cold hardening, indicated by a hardness increasing, followed by some cracks generating, accompanied by their extension and material removal. This process develops in the same mode for all investigated materials, but with different intensity.