Thanks Doug, I wasn't aware there was a difference between normalizing and thermal cycling.
I've been reading this thread, and here's my understanding:
Stress in the steel seeds new grains. The mechanism is complex and I don't fully understand it. Thermal cycling provides a stress/heat environment that allows these grains to form. Multiple quenches from above critical temperature should do the same thing, but more dramatically and at greater risk of cracking the blade.
Grain growth is mostly a function of temperature, and is exponential. Soaking at the critical temperature isn't too detrimental, but getting hotter makes the grains grow bigger faster. Working in a forge without close temperature controls is where you run into problems.
Does that sound right?