Selection and characteristics of stainless steel in different corrosive environments

Application of stainless steel in automobile compression ring
Stainless steel is not only increasingly used to make parts such as pistons, but also to make piston rings. The obvious trend to use stainless steel as a piston ring material first started in heavy-duty applications. It is not only applied to the first compression ring, but also applied to the second and third rings.

The first compression ring is made of nitrided stainless steel. The running surface of the piston ring in contact with the cylinder wall has a high wear-resistant coating, and it also has extremely high anti-pull cylinder performance. The coating, the so-called PVD (Physical Vapor Deposition) layer, is deposited in a high vacuum and is composed of CrN (chromium nitride) with a hardness of up to 1,600 HV 0.050.

Compared with the commonly used ceramic chrome coatings today, PVD coatings have a wear resistance up to 4 times higher than the latter. As far as the performance of the anti-pull cylinder is concerned, significant improvements have been made, especially during the running-in process.

With the ever-increasing requirements for the life of components, the importance of wear resistance is also increasing day by day. Before the first major overhaul of the engine, a running mileage of 1,000,000 kilometers is required. So far, no coating has been able to achieve such high durability, especially when the exhaust gas has a high recirculation rate.

Through the dual treatment of nitriding and PVD on the piston ring, when the PVD layer starts to wear at the piston ring gap, the nitriding layer can ensure the running performance in an emergency. In addition, nitriding also improves the wear resistance of the piston ring side.

In the material application of the second ring, nitrided steel piston rings are gradually replacing chrome-plated cast iron rings. But unlike the first compression ring, they do not use PVD coating.

The oil ring is also made of crimped steel belt and is nitrided, or nitrided with PVD coating.

Therefore, today’s piston ring sets can be made entirely of steel. They meet the demanding requirements of future commercial vehicle engines.