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I forgot to add: railroads are subject to alternating stresses. Even if you'd use annealed or severely tempered tool steel for spikes, they'd work-harden because of the stresses and that would be...

It doesn't make sense for spikes to be .9% carbon tool steel to begin with.
Unhardened, it doesn't make sense because you might as well use 1030.
Hardened, it doesn't make sense because you want...

It will take time for the heat to transfer properly, and you risk burning up one side (assuming you can get hot enough) while the other side is still only red.