A piston ring (34,36) for use in a piston ring pack in an annular ring groove in the sidewall of a piston of a large two-stroke turbocharged uniflow-scavenged internal combustion engine with crossheads to seal against the pressure in the combustion chamber, said piston ring (34,36) comprising: a ring body having: first- and second side faces (46,47) axially distanced by a ring height (Hr), an outer circumferential face extending axially over said ring height (Hr), an inner circumferential face extending axially over said ring height (Hr), and first- and second engaging end portions (38,39) at a ring partition that allows expansion and contraction of said piston ring (34,36), a first transition between said outer circumferential face and said first side face being rounded, a second transition between said outer circumferential face and said second side face being rounded, a medial portion of the axial extent of said outer circumferential face having a first hardness, a first peripheral portion of the axial extent of said outer circumferential face that extends from said medial portion to said first transition having a second hardness, a second peripheral portion of the extent of said outer circumferential face that extends from said medial portion to said second transition having said second hardness, said first hardness being greater than said second hardness, wherein said first peripheral portion extends axially over a first height and is formed by material of the ring body, and said second peripheral portion extends axially over a second height and is formed by material of the ring body, wherein said piston ring (34, 36) has an outer diameter in the range between 400 mm and 1000 mm, and wherein said outer circumferential face bulges radially with a first radius that is 0,5 to 1,5 times the outer diameter of the piston ring (34, 36). a ring body having: first- and second side faces (46,47) axially distanced by a ring height (Hr), an outer circumferential face extending axially over said ring height (Hr), an inner circumferential face extending axially over said ring height (Hr), and first- and second engaging end portions (38,39) at a ring partition that allows expansion and contraction of said piston ring (34,36), first- and second side faces (46,47) axially distanced by a ring height (Hr), an outer circumferential face extending axially over said ring height (Hr), an inner circumferential face extending axially over said ring height (Hr), and first- and second engaging end portions (38,39) at a ring partition that allows expansion and contraction of said piston ring (34,36), a first transition between said outer circumferential face and said first side face being rounded, a second transition between said outer circumferential face and said second side face being rounded, a medial portion of the axial extent of said outer circumferential face having a first hardness, a first peripheral portion of the axial extent of said outer circumferential face that extends from said medial portion to said first transition having a second hardness, a second peripheral portion of the extent of said outer circumferential face that extends from said medial portion to said second transition having said second hardness, said first hardness being greater than said second hardness, wherein said first peripheral portion extends axially over a first height and is formed by material of the ring body, and said second peripheral portion extends axially over a second height and is formed by material of the ring body, wherein said piston ring (34, 36) has an outer diameter in the range between 400 mm and 1000 mm, and wherein said outer circumferential face bulges radially with a first radius that is 0,5 to 1,5 times the outer diameter of the piston ring (34, 36).