Piston ring and process for manufacturing the same

A process for manufacturing a piston ring comprising:

• forming a nitrided layer by subjecting a surface of a steel body to a nitriding treatment, said steel body having a slidable surface which is to face an inner peripheral surface of a cylinder, a first surface and a second surface both connected to the slidable surface by way of corner portions, wherein the nitriding treatment comprises a first step of low-temperature nitriding and a second step of high-temperature nitriding, wherein an outer surface of the nitrided layer comprises a white layer;
• removing a first portion of the white layer which is formed on the slidable surface to expose a diffusion layer;
• and
• at least partially removing a second portion of the white layer which is formed on each of the first surface, the second surface and the corner portions such that said second portion has thickness of not more than 5 .mu.m.

A process for manufacturing a piston ring comprising:

• forming a nitrided layer by subjecting a surface of a steel body to a nitriding treatment, said steel body having a slidable surface which is to face an inner peripheral surface of a cylinder, a first surface and a second surface both connected to the slidable surface by way of corner portions, wherein the nitriding treatment comprises a first step of high-temperature nitriding and a second step of low-temperature nitriding, wherein an outer surface of the nitrided layer comprises a white layer;
• removing a first portion of the white layer which is formed on the slidable surface to expose a diffusion layer;
• and
• at least partially removing a second portion of the white layer which is formed on each of the first surface, the second surface and the corner portions such that said second portion has thickness of not more than 5 .mu.m.