The preferred material for compression rings is a low-alloyed, heat-treatednodular cast iron(KV1/GOE 52). This material is characterized by a high bending strength of min. 1300 MPa and a high modulus of elasticity attributable to a martensitic microstructure and spherulitic graphite structure. For increased stresses a higher hardness is created by varying the martensite morphology (KV4/GOE 56).
In the 2nd groove, alloyed grey cast irons are used in a heat-treated condition (F14/GOE 32). Besides having a high bending strength and modulus of elasticity, an increased hardness of 320 to 470 HB is produced in order to obtain the required wear resistance in the uncoated condition.
The demand for high wear strength is also met by the use of a tempered, alloyed cast iron (GOE 44). This has the benefit of a high bending strength of min. 800 MPa and high modulus of elasticity. The good wear resistance results from the combination of a fine-pearlitic matrix structure and finely dispersed, precipitated secondary carbides.
Unalloyed grey cast iron is used for 2-piece oil rings in the 3rd groove. These ring materials (STD / GOE 12, GOE 13) are characterized by a fine-lamellargraphite structure in a pearlitic matrix and have good conformability due to a relatively low modulus of elasticity.