Effects of intermittent airflow on rolling contact damage characteristics of wheel steels in a low-temperature environment: Airflow humidity

Abstract

In cold regions, warm and humid airflow is easily generated in tunnels with geothermal heat. As trains travel through these tunnels, sudden fluctuations in airflow conditions, temperature and humidity easily cause premature contact damage to the wheel surface. Therefore, the investigation of rolling contact damage behaviour of wheel steels under intermittent airflow could provide support for the stable operation of wheel-rail systems under such extreme service conditions. In this paper, the effects of intermittent airflow with different humidity on the damage characteristics of wheels in a low-temperature environment were investigated using a wheel-rail rolling contact tester. The results showed that the introduction of intermittent airflow mitigated wear but accelerated fatigue cracking during the rolling contact process. With the airflow humidity increased from RH = 5 % to RH = 90 %, the wear mechanism of wheel steels experienced delamination wear, adhesive-oxidative-abrasive wear and delamination-fatigue wear. At low airflow humidity, the increased proportion of small-angle grain boundaries, improved fine grain strengthening and dislocation strengthening provided mechanical support for contact damage resistance. When the humidity of the airflow was moderate, the work-hardening and contact damage at the contact interfaces were weakened, with surface oxidation occurring. Conversely, high-humidity airflow accelerated crack extension on the damaged surface. Additionally, the wheel-rail interface may experience low adhesion when exposed to warm and humid airflow. In summary, reducing humidity in the tunnels is beneficial for mitigating contact damage and extending service life.