View the pictures that I posted of a broken wheel earlier in this thread. The story that came with the pictures (there are more than I posted) stated that the train had been traveling 50MPH at the time it was flagged to be inspected for the defect. The metalurgy of all the metals used in today’s railroads are at quantum step ahead of the metals that were being used 30-40-50 years ago. As can be seen from the pictures I posted - the wheel is destroyed as far as being a wheel, however, the remains are intact and are still afixed to the axle.
The metals of yesteryear did not have near the level of quality control applied to them that todays metals do, not because there wasn’t the desire to have a high level of quality control but because the technology to precisely control the process didn’t exist.
The point everyone seems to be missing is these things start out small and grow over time also it has been cold up this way recently , while not brutely cold still cold , and steel gets brittle when cold and add a sharp pounding will eventually cause damage . As an example we see more broken knuckle pins on inbound train ispections when the temps start dropping into the twenties , so it stands to reason that this happened .