If a one needed to soften a tang up, in order to make peening easier, would it be effective to heat it up to dull red and then allow it to air cool? Maybe repeat once or twice. Can one do this process without affecting the heat treat on the rest of the blade?

I know allowing steel to heat up is often blamed for ruining a blade's heat treat, so if one was deliberately trying to do so, would this method work? If only the tip of the tang is allowed to get red hot, how far would the heat affected zone be expected to spread?

I would say that wrapping the rest of the tang in a cold wet rag should work fine. I've even frozen a knife completely assembled, but with just the little nub of the tang end sticking out of the pommel. A quick heating , and a few hammer taps, and done. It worked fine for me, but I don't know what you are working on. Good luck.....McM

Robin, if there is no grip attached, you should have no problem. Clamp the tang in a vice and heat away. The vice will act as a heat-sink, the heated area will cool pretty quickly, and you should have no issue with heat spreading.

In the swords I make (using 5160 or 1075 spring), I leave the tangs untreated - as per Dr. Hrisoulas's recommendation. When assembling, I find the metal needs to be peened while hot to prevent cracking. Pommels can become uncomfortably warm doing this, and some adhesives could be affected, but I haven't run into any disaster so far.

I did exactly this with a Kovex Ars-sword a few weeks ago, during a pommel and grip replacement. It turned out they had brazed the pommel in place :eek: So I had to cut the tang below the pommel, and reshape (not a big deal really, the grip was way too long anyway)
But that meant that the new tang end was from heat treated rock hard area.

I used propane torch and vice, worked a charm. I have done this once before sticking the tang end into the charcoal bed of my barbecue, when I still had lovely smoldering coals left after the dinner was done. It got enough heat, and cooled really slow wiht the coals :)

Is it safe to do a full hot peen on a primarily organic Migration hilt?

This is all theoretical at the moment. I am considering perhaps acquiring a blade and trying my hand at doing a Migration sword.