Tver State Technical University, Tver, Russia

V. V. Izmailov, Dr. Eng., Prof., Dept. of Applied Physics
K. A. Sakharov, Assistant Prof., Dept. of Metals Technology and Materials Science
M. V. Novoselova, Cand. Eng., Associate Prof., Dept. of Applied Physics
L. E. Afanasieva, Cand. Phys.-Math., Associate Prof., Dept. of Metals Technology and Materials Science, e-mail: ludmila.a@mail.ru

Samples of high-speed steel R6M5 after various technological processes were investigated using metallographic, X-ray phase analysis, and tribological tests: hardened using the standard technology consisting of bulk quenching and triple tempering, after laser cutting with nitrogen purging, after laser cutting and cryogenic treatment in liquid nitrogen. Differences in the phase composition and microstructure of the samples are demonstrated. After laser cutting, an increased content of residual austenite, about 30%, was revealed in the hardening zone. The microstructure of the steel near the cut surface has a cellular structure, the average size of the dendritic cell is about 3 μm, and the microhardness is about 8600 MPa. Cryogenic treatment reduces the amount of residual austenite to 9%, while the cellular microstructure of the cast metal is preserved. The microhardness of the steel increases to 9800 MPa. In the samples hardened using the standard technology, the microstructure is represented by martensite and carbides, and residual austenite is not detected. The steel microhardness is approximately 8300 MPa. The results of experiments to determine friction characteristics are presented: the parameters of Coulomb’s two-term friction law F₀ and f_C, the friction coefficient f_A in accordance with G. Amontons' wellknown one-term friction law, and the parameters of the specific friction force τ₀ and β in accordance with the well-known tribological linear dependence of the specific friction force on the actual contact pressure. It is shown that cryogenic treatment results in a 20 % reduction in the friction coefficient in the contact between R6M5 steel specimens and a metal counter specimen. The specific friction force slightly increases after cryogenic treatment.

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