Abstract: A piston ring includes a first radial flank; a second radial flank; and an outer rounded circumferential surface constituting a contact face of the piston ring. The rounded face has a circumferential crest line situated at a distance from the first radial flank which is more than one half of the axial piston ring height. The piston ring further has facing end surfaces defining a ring gap; and a circumferential groove provided in the outer rounded circumferential surface and extending axially from the second radial flank to the crest. The circumferential groove terminates adjacent each end surface at a distance therefrom.

Abstract: A cast-iron piston ring for a piston of an internal combustion engine includes a ring composed of cast-iron and having a circumferential surface; a nitrided layer covering the entire circumferential surface of the ring, the nitrided layer including a diffusion layer and a connection layer disposed above the diffusion layer in which the diffusion layer and the connection layer both cover the entire circumferential surface of the ring; and a metal layer which is electrodeposited onto the connection layer, which is composed of a metal having a hardness which is less than that of the connection layer, and which has a thickness of less than 5 &mgr;m.