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Ed, love you do death, my online friend. But soaking is very much an important part of certain alloys. Which alloys? The ones with a good % of alloying in them. Simple carbon steels need not be soaked beyond a good thorough heating to ensure it's even, then quenched.
52100 and O1 have a bit more alloying in them, hence the soak. Some of the most well known metallurgists on the planet who have torn 52100 apart every way you can and looked at it with very expensive scopes, etc etc etc have come to the conclusion that the soak is best for certain alloys. This is very common practice in alloyed steels. Take A2 for example, the next step up above 52100 in many ways. If you were to simple equalize and quench that steel without the recommended soak, your HRC is not going to be very good at all. The chromium has that carbon tied up, and you have to release the carbon to get the hardness somehow. Either TIME, or TEMP. Too high of a temp, as you know, brings it's own problems.
I do recall the test you did with soak vs no soak on a given alloy. I don't recall the alloy but I think it was 1084. I would not soak that one at all, beyond equalizing for a minute or 2. Regardless of the alloy, your test indicated that the knife that DID get the soak was chippy. But you used the same temper temps, IIRC, for both samples when you came to this conclusion.
BINGO. I would totally expect that to happen. 52100 gets no soak, tempered at 350f, maybe not too chippy. 52100 that gets the soak, tempered at 350F, yeah....maybe a little chippy.
The main problem I have with "Industry" 52100 heat treat is the recommended aus temp of 1550F. Good for ball bearings, not so good for knives. 1475F gives the best HRC (assuming we have taken care of any coarse spheroidizing issues), with a short soak to get that carbon in solution. If you used 1475, equalize with no soak at all, then quench, I would expect a sub par HRC. 1475F with 10 minute soak should get 66-67+, and more than likely, a higher temper than you would use otherwise if no soak employed.
I have found the most every alloy I am needing to bump up my temper temps higher than the charts. I use the soak, and usually a fast oil quench, even on 52100.
However, there are more than one ways to skin a cat. I try to think of skinning cats as often as I can. Infernal creatures.
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