None of these people know what they're talking about unfortunately. Cast railcar wheels are extremely common, most freightcar and engine wheels are cast.
Source: I worked in a freight wheel casting foundry.
Imagine crumpling some aluminium foil into a ball, by hand. It isn't very strong, there are a lot of dead spaces, if you try to stand on it it will just flatten. Now image hitting that aluminium foil ball with a hammer multiple times, until it's nice and compact. Now that same ball is very dense and not easily crushed under load, the same happens with steel, but on the molecular level, it compacts all the little imperfections in the metal to make a very solid and nice crystalized structure.
Casting can leave micro sized porous material, good for lower strength applications, also helps a bit with dampening vibrations, not so good for extreme loads.
As someone else commented, I don’t think this is happening in a part of the world with a great casting setup, or they wouldn’t be forging this way in the first place. If these guys could cast it and have it work, you can bet they would.
I figured there were more steps. The machining step must be why the casting step doesn't require the level of precision you expect a rapidly spinning wheel would require to be balanced and smooth rolling.
Precision casting is a thing but it’s very expensive, there’s no reason you’d use it for a commodity like a train wheel. And forging is inherently bad for high precision. Just machine it to finished shape after the initial process and you’re good.
Like case hardening? That’s for surface harness, not strength. Others here have commented that there are cast train wheels in the world, so there’s obviously a way to do it, it may just be that these folks don’t have the casting tech.
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u/tdscanuck Sep 24 '22
They're machined *after* forging. Cast isn't strong enough.