1. Field of the Invention
The present invention generally relates to railroad wheel steels. More particularly, it is concerned with those railroad wheel steels that are alloyed and/or heat treated to resist both wear and thermo-mechanical deterioration, especially in the tread (and/or flange) regions of such wheels. The terms “spalling” and “shelling” are widely used in describing such thermo-mechanical deterioration. Spalling generally refers to loss of wheel tread material as a result of metallurgical damage created by excessive heat that results from sliding of railroad wheels during train braking operations. Shelling generally refers to loss of wheel tread material as a result of deterioration arising from mechanical stresses.
Various problems arise from each form of tread material loss. By way of example only, thermo-generated deterioration of a railroad wheel's tread can quickly create flat spots on the wheel's outer surface and thereby produce the undesired quality known as “out-of-roundness”. Moreover, when railway wheels experience thermo-engendered deterioration, surface cracks tend to propagate from such deteriorated areas and cause potentially dangerous defects in contiguous wheel regions. Similar surface cracks are also created as a result of relatively slower mechanically generated deterioration. Aside from their catastrophic accident causing potentials, wheel defects such as these are also known to increase wheel/rail dynamic forces that produce consequential damage such as broken rails and accelerated track deterioration. The railroad industry is therefore constantly looking for ways to minimize every aspect of thermo-mechanical deterioration of railroad wheels while still preserving, as far as possible, their wear resistance qualities.
2. Description of the Prior Art