Tribological Characteristics of Cast 120X15, 120X15Ю and Standard 20X13 Steels in Conditions of Boundary Friction

Processy litʹâ, 2019, Tom 135, №3, p.59-66

Abstract

Received 10.04.2019

UDK 669.141.25:539.62

The article presents the results of the study of tribological characteristics and the process of formation of the secondary structure of deformed steel 20X13 and cast steels 120X15 and 120X15Ю under conditions of boundary friction (water was fed into the friction zone). Initially, the microstructure of the steel 20Х13 is a ferrite-carbide mixture consisting of high-chromium ferrite and carbide type Cr23C6, and the microstructure of cast steels 120X15 and 120X15Ю is a ferrite-carbide mixture consisting of high-chromium ferrite and carbide type Cr7C3 with eutectic (α + Cr7C3) along the boundaries grains. Tests of specimen s wear under conditions of sliding friction were carried out according to the ring (counterbody) – block (specimen) setup. Sliding velocity was 1 m/s, and the specific load was 5 MPa. The phase composition and parameters of the fine structure of the working surface of the sample steels before and after friction tests were determined using X-ray structure analysis in iron Kα-radiation. It has been established that the wear rate of cast steel 120X15Ю is 3 and 2 times less than that of steels 20X13 and 120X15, respectively. It should be noted that in the surface layers of steel 20X13, after friction, α↔γ transformations are not observed, and friction energy dissipation occurs due to thermal fields and changes in the fine structure of the α-phase. The structure of the surface layers of cast steels 120X15 and 120X15Ю undergoes more significant changes in the process of boundary friction, and, in this case, the initial α-phase has a greater ability to accumulate energy from the outside due to a change in the fine structure without destruction. An additional factor for the dissipation of friction energy is the occurrence of α↔γ transformations in the surface friction layers of cast steels. At the same time, for the cast steel 120X15Ю a dynamic equilibrium is established between the α- and γ-phases, and an almost equal density of dislocations in the α -and γ-phases is established. This leads to increased wear resistance of cast steel 120X15Ю compared with the others. These results can be used in the development of cast steels for the flowthrough parts of unified centrifugal pumps such as CN 50, etc.