PISTON RINGS OF NITRIDABLE CAST STEELS AND PROCESS OF PRODUCTION

摘要

The present invention ('PISTON RINGS OF CAST NITRIDABLE STEELS AND PROCESS OF PRODUCTION') describes an alloy and the process for the obtainment of cast parts suitable for piston rings of nitridable steels having a relatively high content of N and having low contents of Si. In this invention the fraction of M₇C₃ eutectic carbides is reduced to fractions of less than 2.0% by weight through the substitution of part of C by N and, in addition thereto, these eutectic carbides are transformed into M₂₃C₆ carbides during the stage of heat treatment. This transformation is accompanied by an alteration in the morphology of the carbides, reducing the maximum size thereof and the continuity thereof in the microstructure of the material. This microstructural alteration of the material of the present invention is due to the chemical composition (low contents of Si and relatively high contents of N) and appropriate heat treatments. The rings of cast nitridable steels having low contents of Si and high contents of nitrogen obtained in the present invention have overcome the limitations imposed by the processes and/or materials belonging to the present state of the art, these being: limit of loading whereunto the rings of cast iron may be subjected, dimensional limits of the process of shaping wires of stainless steels, and formation of coarse carbides in the alloys proposed in the document US 20120090462. The following table shows the limits of composition for the material.