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Good knowledge.
I didn’t realise you would harden first then grind, then harden again!
I (think I) know the case hardening process is something to do with the steel being too low in carbon to be hardened so carbon is ‘introduced’ into the surface and then hardened(?).
I have a DT teacher neighbour who loves a technical challenge and is a cyclist (sensible hub gears and ugly bikes) so I might ask him, he often comes up with genius low-tech workarounds, clever chap.
absurdbird
Uhhhh, you're crossing over my knowledge bands here now!
I've case hardened and ground thrust bearing races before. You case harden, then grind the surface. I don't know how deep the case hardening goes, but the divots that the ball bearings make are definitely deeper than the case hardening. So, to get a new, perfect surface, you'd need to dress the surface back to remove the divots, then case harden or nitride or whatever was done, then grind again. I don't know how curved surfaces are ground, there's a chance it might be done with something hard like silicon nitride balls and a grinding paste.
Like I said before though, I'd wager you could do similar if you were to pack the races with silicon nitride balls and a fine valve grinding paste, then spin the assembly with a drill. If you just took the worst off, you'd probably turn a rough headset into a perfectly useable one. even regular ball bearings are probably hard enough to do this.