OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 4 2024 Non-structural cementite is not allowed. Phosphide eutectic may be present in the form of small uniform inclusions or broken meshes, and triple phosphide eutectic with plates is not allowed [6]. The appearance of cementite in the structure leads to brittleness [7, 8]. According to GOST 7133-80, rings made of cast iron with spheroidal graphite as a metallic base should contain fi ne, sorbitic and medium plate pearlite. The percentage of cementite in the form of small inclusions should not exceed 10 % of the section area, and the percentage of ferrite should not exceed 10 % of the section area. There are techniques of the optical-mathematical method of describing metallographic images that allow estimating the percentage of inclusions of various phases of high chromium cast iron [9]. The problem of improving the reliability of CPG can be solved by comprehensive studies of possible operational changes in materials, using modern testing, research techniques and analytical programs. With any dynamic and thermal impact on the rings during operation the internal structure of the material changes, the plastic deformation zone acquires characteristic features. This is confi rmed by layer-by-layer texture analysis of metal in the brittle fracture region for an undeformed new specimen and a specimen with defects after operation [10]. An increase in dislocation density, changes in the microstructure, and possible appearance of textural inhomogeneities can be studied using metallographic methods and diff raction of X-ray and electron diff raction [11–14]. The analysis of literature sources on this subject allows us to draw conclusions about the relationship between changes in the structure and operational properties of the material. In the work [15] the researchers found out that when the material of the working parts of submersible pumps made of cast iron is changed, when the lamellar form of graphite inclusions is changed to spherical, such operational characteristics of cast iron as strength and ductility are signifi cantly improved, but there is an increased volumetric shrinkage and worse fl owability in liquid state. These factors should be taken into account when selecting the technology of compression rings manufacturing. A similar nature of the infl uence of microstructure changes on the material properties is observed for cast irons and steels. Analysis of changes in the microstructure and crystallographic texture of ferritic steel during stress corrosion failure (SCF) using scanning electron microscopy made it possible to determine the size and type of nonmetallic inclusions, the elemental composition of corrosion products, and the nature of fracture in the zone of SCF [16]. Within the framework of X-ray diff raction analysis (XRD), which took into account the shape and size of grains-crystallites, crystallographic texture, atomic occupancy of the crystal lattice, atomic displacements, Debye-Waller factor and instrumental line broadening, the parameters of the fi ne structure of ferritic steel in the fracture zone and in the zone free from the CRN were estimated. It is shown that the fracture region is characterised by a high density of introduced edge-type dislocations, strong elastic distortions of the crystal lattice and a relatively small size of coherent scattering regions (CSR). Many studies on various steels show that increasing the strain rate at high temperatures increases the threshold strain, which occurs before the onset of dynamic recrystallization of austenite. When boron microalloying is used, the opposite eff ect is observed, i.e. the threshold strain decreases. The presence of boron in the solution promotes the formation of grains at the boundaries, which prevents the rearrangement of atoms and facilitates the migration of these grains. Rapid dynamic recrystallization improves the ductility of steel and also promotes grain refi nement, which reduces its brittleness [17–18]. It is also interesting to study the eff ect of the stress-strain state on the propagation of cracks in quasicleavages of steel subject to embrittlement due to the presence of hydrogen. The role of hydrogen in the crack propagation mechanism was investigated, and it was found that the crack path in quasi-scales in hydrogen embrittled ferritic and ferritic-perlitic low-carbon steels is determined more by the nature of the stress-strain state than by the microstructure or the crystallographic orientation of individual grains [19]. There are new technologies for the production of steel piston rings, which provide for surface grinding [20], surfacing wear-resistant coatings, including the development of a method of three-layer hardening of its surface. This method includes carbonitriding, ion implantation of titanium nitride and then sulfi ding, which leads to improved processing and increased wear resistance of piston rings [21]. Electroacoustic sputtering method can be very eff ective in hardening of piston rings [22]. The resulting nanocrystalline
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