depends what size you mean? do you mean a 3m for behind a tractor? if so ours had some kinda hardened steel skids, but once they wore away, i just bent some 50x12mm flat and welded them on. wouldnt even bother with hardfacing, as they will last ages!
I'm pretty sure the skids on a Kuhn/JD bed are normal mild steel but if they're all worn out its going to be a much better job to replace them all. Kuhn are normally very well priced on WEARING parts so price a new set up before messing about bodging them....