If you get a look at the alloy makeup for train rails, you'll see why that is. It's potentially quite hard -- carbon runs up to 0.80% by the ASTM standard, and it contains manganese (1%), which augments the hardening effect of the carbon. As-rolled, it comes in around 400 Bhn (Rc 43). It may actually be harder when re-rolled, because the thinner sections generally cause more work-hardening.
On top of that, older-spec rails can contain relatively high levels of sulfur, phosphorus, and silicon. You get some weird microstructures when you heat that and re-roll it.
Rolled as rails, the steel is intended to have a totally pearlitic structure. It's hard and strong but other properties, such as elongation, can be lousy. So it's likely to be nasty to cut, a bugger to weld, very hard but with very little ductility.
'Great for a railroad. Not bad for a bedframe. Otherwise, IMO, it's junk.
Well, rails are from around 0.50 to 0.80 percent carbon -- newer rail has higher carbon. As rails, it's hypoeutectic pearlite -- layers of carbide laminated with layers of ferrite. The carbon may go into solution when it's heated and re-rolled, but don't count on it.