It is highly unlikely they are so hard as to defy a die, hard metal tends
to be brittle, not a desirable feature in an axle, it may be relatively
hard but using a cone or other nut from the opposite side of the
removed axle is one way to try cleaning the threads, a very fine
file is another, absent the proper sized die. If the bunging is not
circumferential the affected part could be filed down.