Double heat treating?

[MostHostLA]

Since I can't find any information about this online, or from any of the scientific reading I have been doing on the subject, I would like to ask anyone with experience about the science behind this topic.
The real goal here is to have a hopefully definitive result when you search Google...

While I don't really see a problem with it, short of having less carbon content after the first go, can you heat treat more than once?

Scenario:
Let's assume you grind your knife blade off a blank (what most beginners I Imagine would do instead of forging).
You think you are happy with it, and you therefore take it through the necessary hardening(austenetizing)/tempering steps.

Thereafter, you clean it up and find that your lines are a mess or that there is a big dip on the blade or, well any defect that you need to re-normalize and work on a softer metal to fix...
So, you take your screw up, you heat it to oblivion and let it soak, you then dump it overnight in vermiculite and work at it again.
After you are done again, you repeat the hardening/tempering process.

Questions:
What are the real downsides to this - in terms of edge retention/hardness?

Do they get worse if your knife was more properly forged instead of ground up?

Bonus Question: would pattern welded damscus be any worse off?

Assumptions: (For practicality)

1084/1080 as the steel of the blank.
And 1084/15n20 for the pattern welded

Real quench Oil(s) Parks AAA or Parks50 and not canola or other low cost substitutes.

Forge heat treatment controlled by temp gun/other accurate(ish) means - yet not as accurate as a proper oven.

Thanks in advance to anyone for any creative contribution. And a triple prehemptive thanks to those able to provide some scientific based science behind their answers....

 

[Stuart Davenport Knives]

When talking carbon steels/carbon damascus and the scenario you described, there would be no problems at all with hardness. I really don't understand your second question.

Let's say the starting microstructure was correct and your heat treat was fine, as long as you aren't planning on drilling/grinding/etc, you can simply just re-harden the blade like you did the first time, but I understand in your scenario you are wanting to address some cosmetic changes......

However, if the heat treat was fine and you ARE planning on drilling/grinding/etc, you can do a temper anneal by soaking the blade at 1200°F for two hours, then reharden. In a forge that really isn't feasible, so I would normalize the steel at ~1650°F (1080, 1084, 15n20), give it short soak, and let it air cool. No need for an extended slow cooling in vermiculite unless you're planning on drilling due to the lamellar pearlite structure being tough on drill bits. After the normalizing, you can cycle the steel once or twice around 1500°F and then reharden.

 

[mooniesdl3]

With the correct setup, grinder and belts and misting setup, you can grind hardened steel, some of us prefer it for most steels as long as it isn't too thick.