Mechanism of Plastic Deformation and Worn Powder Generation

Abstract

As the first step to elucidate the phenomena taking place during rolling contact between a rail and a wheel, some experiments on rolling contact have been performed using high carbon steel.A specimen rod cut out from a real rail was shaped into a circle of 500mm diameter and two small wheel-like pieces cut out from a real wheel were attached to both ends of an arm which rotates on the center of the circle. The test rolling contact conditions were of low loads and low speeds.After every 30 to 120 minutes of rolling contact, the test pieces were taken out and the changes in their sectional profile, wear and surface residual stress were measured. After 11 hours of rolling contact, the plastic deformation in their surface and the profile of worn powder were examined under the optical and electron microscopes.The results showed that plastic deformation causes a scaly pattern to develop on the surface of the rail specimen; cracks initiate in this area and propagate inward, making the specimen to flake from the surface. Meanwhile the worn powder, which has been torn off, adheres to the wheel surface and forms a film of about 5μ in thickness. The greater part of the worn powder after the rolling contact has become steady is the result of the adherent film on the wheel being torn off again.The amount of wear after one cycle of contact is nearly the same for both the rail and the wheel pieces. This indicates that the adherent film on the wheel contains the worn powder originating from both rail and wheel. Thus the mechanisms of plastic deformation and generation of worn powder during the rolling contact have been made clear.