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The effect of heat treatment (tempering temperature after quenching) of medium carbon steels (steel 45 and
steel 50) on tribological indicators at sliding friction without lubrication in connection with the change in strength
and rheological elastic properties of steel, controlling the dissipative properties of the frictional contact has been
studied. Tribotechnical tests were conducted according to two schemes. A high-temperature tribometer was used
for “soft” friction according to the “ball-plane” scheme, which allowed varying the temperature of the friction
contact. Influence of load-rate modes was studied in more “hard” conditions on the friction machine under the
“finger-disk” scheme. Substructural transformations of steel caused by heat treatment were evaluated by changes
in amplitude-dependent internal friction on a torsion pendulum-type machine, which also allowed measuring frictional damping (contact internal friction) in the preliminary displacement mode. The interrelation between hardness, elastic modulus and internal friction of steel and wear resistance, wear capacity, friction coefficient and the
level of frictional damping has been established. It is shown that the growth of elastic modulus and increase of
steel relaxation resistance after the appropriate heat treatment are conjugated with the development of adhesion
and setting, which, as topochemical reactions in the solid phase, are the leading forms of contact stress relaxation
under the above conditions. Correlation of tribological indicators of external friction with amplitude-dependent
and relaxation (temperature-dependent) internal friction taking into account structural state of steel and friction
temperature regime is established. Substructural preconditions, dynamic relaxation mechanisms of hardening and
load-temperature friction conditions under which martensitic structures exhibit abnormally high wear resistance
and significant growth of frictional damping level are considered. The tribological analogue of the Porteuen - Le
Chatelier effect, manifesting in the form of frictional self-oscillations in the range of temperatures of dynamic
deformation aging is established. A treatment of the nature of the Kael-Ziebel effect, the temperature-rate and load
localization of which in friction is associated with the temperature range of dynamic strain aging with SnookKester relaxation superimposed, is proposed.
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