Can anyone here tell me how to take a piece of O-1 tool steel that is 1/2"X2"X24" and harden it to RC 50-52 and keep it flat within .010"?
That is a hard one.
Even though it is a fairly stable metal as metals go it's going to take off when you quench it.
If you give it a go make sure your quench tank is deep enough
and hold it perfectly vertical and get it all the way in the tank as quickly as possible. Your going to get some oil coming out and it will probably be on fire. So be prepared.
This is one where you might be better off taking to a heat treat facility and having them sneak it into a batch of someone else's stuff and then do their magic to it.
If you have a machine shop and it is cost effective you can take a couple of stainless plates
larger than the piece and clamp it between them. They have to be flat of course. Each one should be thicker than what your trying to keep straight.
The thicker the better.
Use only stainless high tensile bolts and nuts. Lots of them they will be carrying a lot of load. Remember the high temp never-seize! You have to drill your clamp bar faces and slot them to get the oil to the steel quickly or you might not get a fast enough temperature drop to give you higher than 52 Rockwell.
You may need to use water to get to 52 with the resulting mass. Once you get the fixture built clamp the tool steel between the halves, torque the nuts to a good high spec and heat treat as you normally would. Try oil and if the doesn't get you there move to water, ice water, ice brine etc till you are over 52.
Then draw back down to 52. If you quench in anything quicker than oil you must draw back immediately because the edges that were fully exposed will have a lot of stress in them. If you don't get it in to the tempering oven immediately it could crack. Definitely don't leave it on the table and go to lunch. You might have pieces when you come back.
Let it heat soak in the tempering oven for a good long time especially if you had to quench in something other than oil.
Here is how it works.
The stainless expands at a much, lower rate than the steel.
As the steel inside expands the stainless frame becomes a press putting the tool steel under huge amounts of force.
The stainless is also much more stable than the tool steel and does not want to move when quenched.
The stainless clamp continues to hold the tool steel flatter till it has cooled. As the assembly cools the pressure on the tool steel lessens. Then you just need to temper it back to 52.
I'm sure there are other ways.
We used to make little flat washers that were used as intake valves for very high pressure air compressors this way.
If you were to heat treat them normally you ended up with a wave washer. We would load a hundreds on a stainless threaded rod with the nuts machined true. Torque to spec then heat treat. When we backed off the nuts the washers were flat enough to go directly to lapping. Life was good.
The process is sound you might have to do some creative thinking to adapt it to what you are doing.