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Olivier Barrau
Abstract
Friction and wear study of hot tool steels
Olivier Barrau - 14 december 2004
In all the operations of metals forming, friction plays a determining part on the quality of the products obtained. The lifespan of the tools is limited by the damages which develop on the tool surface. This work constitutes a contribution aiming to describe the behavior and to predict wear in friction of hot work tool steel. For that purpose, the followed methodology is articulated around three complementary parts.
The first experimental work allowed us to highlight the mechanisms controlling the hot wear of the tool steel. The influence of the test temperature, the geometry of the test specimen and the surface quality of the tool steel (presence of a nitrided coating) on friction and wear was studied. A cycle of damage was then imagined where the plastic deformation of the surface of the pin controls the wear by loss of matter.
A stage of validation of the assumptions leading to the damage cycle was carried out. This validation is based on many bibliographical work and a complementary experimental work. The experimental study highlighted the role of the load applied and the temperature on the plastic deformation. The ductility of steel was estimated in hot traction and hot torsion. Moreover, stopped tests made it possible to build wear's kinetics of the pins.
Lastly, a model of damage was identified. This model is based on a criterion of rupture of ratchet effect. That expressed a cumulative total of the plastic deformation on the surface of the pin before debris emission. A numerical modeling of friction was necessary to reach all the parameters of the model of wear. The predictions provided by the model were compared with the results obtained at the time of the stopped tests.
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