In fact many simple metals, those lacking inherent sources of high strain energy, actually require deformation in order to recrystalize upon subsequent reheating. A misinterpretation of this concept may very well be the source of some of the false notions we have about improving steel with hammering. You see, steel is not a simple metal; it is very complex with all kinds of inconsistencies built right into its lattice. Steel can recrystallize every time it is heated to the appropriate temperature with no help at all from the hammer, although hammering can add to the turmoil.
With all this in mind, one needs to reexamine the claims of mechanically refined conditions at any temperature while remembering that any effects from plastic deformation will be rearranged as soon as the metal is heated to anywhere near recrystalization by the very process that makes stress relieving and annealing possible. To be entirely successful, quench hardening heat treatment requires those same processes. Many of the claims of improvements via deformation can be in direct opposition to proper heat treating.
As we have already discussed, steel will form all new crystals when heated above the recrystallization temperature, and that hammering can add points for this process to occur, but what happens if you hammer at a temperature beyond the recrystallization point? Each hammer blow will introduce energy into a system that is trying to equalize itself; this new energy will then initiate fresh nucleation points and more new grains. Proper forging temperatures are a balance of the need to move the metal and keeping pace with the rate of grain growth. But for all of the frustrations steel can give us, it has some wonderful safety mechanisms built into it that can save the work of even the most incompetent smith.
Since steel has the ability to recrystallize just fine all on its own, a process called normalizing becomes very significant to bladesmiths. Quick heating to the recrystallization temperature, while just leaving the poor metal alone to do its thing, will wipe the slate clean, even out all of the problems our inconsistent pounding can bring, and refine the grain better than any of our magic hammer taps.
But what about forging refining the grain? Isnt that what bladesmiths do? Yes, but a wise smith with the knowledge of what steel is really capable of will get out of its way and let it fix itself much more efficiently. If finer grain is superior for our purposes (and in most cases it is), then why only have finer grain in just the spots our uneven hammer blows managed to catch? Why not relax and let the heated steel do the work and make the entire blade uniformly fine?
Any time I have used various thermal treatments alone to refine grain size, and then compared the fractured grain appearance to samples that I had hammered into submission, the former were always smoother and more uniform in appearance. This should come as no surprise when one considers how complete or uniform ones hammer blows could be when compared to the action of the entire internal structure of the steel at work. Also worth mentioning is an interesting phenomenon which metallurgists have observed, and bladesmiths need to consider. If steel is only lightly deformed, there will be enough uneven points of nucleation created for many little grains to form around a few large grains. Since large grains grow at the expense of smaller grains, what we have done in this circumstance is created a monster and surrounded it with all it can eat. Overall, this would result in an uneven grain coarsening effect, which one would not have if they had just let the steel do its thing, or at least really moved the steel enough to totally rework it. This would render the idea of packing with a few light blows at the end completely counterproductive.
