Piston ring with localized nitrided coating

A method of making a crack-resistant piston ring, comprising:

• providing a piston ring, wherein the piston ring has an upper face, a lower face, an inner perimeter wall, and an outer perimeter wall that extends around the piston ring from the upper face to the lower face;
• the outer perimeter wall having upper corner region disposed adjacent the upper face, a lower corner region disposed adjacent the lower face, and an annular cavity in the central portion of the outer perimeter wall extending between the upper corner region and the lower corner region along the length of the outer perimeter wall;
• forming a nitrided conversion layer penetrating an exterior layer of the piston ring;
• performing a grinding process on the outer perimeter wall, wherein the grinding process includes removing the nitrided conversion layer from the upper corner region and the lower corner region, thereby exposing the underlying piston ring in the upper corner region and the lower corner region forming a band of nitrided conversion layer between the upper corner region and the lower corner region;
• and
• depositing a PVD nitride layer on the outer perimeter wall of the piston ring.