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Catherine Vergne (V.2)
Abstract
Oxides influence on friction of a hot working cast iron
Catherine Vergne - 18 december 2001.
Hot rolling consists in forming a metal slab by compression between two
parallel rolls rotating in opposition.
The roll superficial oxide layers play an ambiguous role. On the one hand,
they allow the metal sheet to be driven between the rolls. On the other hand,
they can cause damage on the surfaces of rolled products and tools during the
thermo-mechanical forming process.
The aim of the present study was to understand the oxidation-friction
interaction mechanisms between two materials involved in hot rolling process.
The conception and the realisation of a high temperature pin on disc
tribometer, in the CROMeP, has been achieved through this study.
The investigation has been made through three directions : oxidation, heat
transfer and tribology.
A change of friction coefficient evolution was observed with a non-stationary
period. However it proved dependent on the nature and on the thermal regime of
the initial contact.
SEM observations of wear tracks, both on pin and disc, led to the elaboration
of a phenomenological model to explain the debris evolution mechanisms in the
contact.
In spite of an evolution of the damage mechanisms, no significant modification
of friction coefficient was noted when the normal load and the sliding speed
were modified.
This non-evolution of friction was explained by a constant oxide-oxide contact
(hematite / hematite).
X-ray diffraction analysis, conducted both on pin and disc, in wear tracks as
well as out of wear tracks, showed the modification of the growth texture of
the oxide scale when the X-ray beam depth and the friction conditions were
modified.
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