The gas nitrided stainless steel pistoring (referred to as the gas nitrided ring in the following) was placed in mass production in 1983 to improve the durability of small diesel engines and leaded gasoline engines. Since their introduction, gas nitrided rings with their stable performance have replaced many chromium-plated rings with low durability and thermal-sprayed rings with weak coating strength. As a result of their superior wear resistance, the application of gas nitrided rings has expanded to a variety of engines1). After a steady increase in production over the past 10 years, gas nitrided rings account for more than 20 percent of the total piston ring production at our plant today. Gas nitriding contributed significantly to the change of the base piston ring material from cast iron to steel in Japan.
During this period, however, requirements for piston rings have grown more sophisticated as a result of improvements in engines. At the same time, as the application of gas nitrided rings expanded, various shortcomings became apparent, which have been dealt with by improvements in material and ring shape.
This report outlines the developments and improvements we have made of gas nitrided piston rings. It will also describe the development of partially nitrided side rails, now in mass production, for 3-piece oil rings. These side rails are processed by an ion nitriding method rather than the gas nitriding in order to provide a system that minimizes the wear of piston oil ring groove