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The dissertation is devoted to determination of structural parameters of
formation of nanocrystalline structures on carbon and low-alloyed steels by surface
mechanical-pulse treatment, investigation of their influence on tribological
properties, corrosion resistance and hydrogen embrittlement, and on workability of
steels under the mutual action of mechanical loading and corrosion-hydrogenating
environments.
It has been established that parameters of nanocrystalline surface layer and its
physical and mechanical properties depend on treatment regimes and type of
technological environment, which enables forming a surface layer with adjustable
structural state and properties. It has been shown that size of crystallites in the surface
layer of the treated steel influences on the surface microhardness: it increases with
decreasing crystallite size.
It has been found that the surface layers, formed on the 40X and 65Г steels by
mechanical-pulse treatment, had nanocrystalline structure even under heating up to a
temperature of 500 °C. The regularities of changing the size of crystallites in the
surface layer in a nano scale range with an increase of heating temperature have been
established: the size of crystallites is decreased at increasing temperature up to
300 °C and it is increased at higher temperatures.
Friction coefficient of steels decreases significantly after their mechanical pulse
treatment, which correlates with reducing crystallite size of the steel surface layer. It
is reduced in almost four times for the 45 steel with nanocrystalline surface layer in a
pair of friction with the ШХ15 steel under oil wear.
It has been found that the surface layer with nanocrystalline structure formed on
the 45 steel by mechanical-pulse treatment is characterized by lower hydrogen
permeability (hydrogen diffusion coefficient is in 1.3–4 times lower) and higher in
1.5–4.4 times efficiency of hydrogen trapping in comparison with the untreated steel.
Therefore, it serves as a barrier for hydrogen penetration into the bulk material. It has
been established that nanostructurization of the steel surface using mechanical-pulse
treatment by multidirectional deformation in an oil technological medium provides
the highest resistance of the steel to hydrogen embrittlement.
It has been shown that alloying the surface layers of the 35 and 45 steels by
nickel, boron and nitrogen during mechanical-pulse treatment can offset the negative
influence of intensive plastic deformation on their corrosion resistance.
The nanocrystalline surface layer is characterized by high wear resistance under
oil and oil-abrasive wear and under the action of corrosion-hydrogenating medium of
diethylene glycol, as well. It significantly increases limits of fatigue and corrosion
fatigue, and also contact fatigue of treated steels.
The method of mechanical-pulse treatment of equipment components made of
carbon and low-alloyed steels with formation of surface nanocrystalline structures
have been implemented at MCC “Lvivvodokanal” and PJSC “Kohavynska Paperova
Fabryka”, showing increase in service life of the treated components in 2.5–3 times.
Key words: nanocrystalline structure, mechanical-pulse treatment, friction
coefficient, mechanical properties, wear resistance, hydrogen embrittlement, fatigue,
corrosion fatigue, contact fatigue.