How coincidental the timing of this thread is, as I began metallography work on Mr. Pattons, 5 hour soaked O1 today. One persons word is never good enough for us to go on for proof, however let me reiterate the facts that not only did Mr. Pattons experiment yield the predicted results, but I mentioned others who have done the same with 52100, I have done extended soak times with O1 (not as extreme as 5 hours, since it is well beyond the realm of usefulness). Ray Kirk is no slouch in the knifemaking field and he told us that he went as far as to soak 52100 for 24 hours with the same results.
I am confident that any others repeating the experiment will get the same results, since any metallurgical text will confirm the concept. The case is looking pretty good on this one folks.
I have looked over pg. 68 of the excellent writing to which we are referring and there are no contradictions at all, it entirely supports previous conversations as well as the experiments we have mentioned. Then entire section deals with why
temperature control is important. On that chart the 2 hour growth rate parallels the 6 minutes and they are continuously increasing in temp, clearly showing how irrelevent time is in comparison to temperature. Also be aware that the only part of this graph that would be within the range of proper heat treating would be the lower left section below 1500F. Allow me to quote the text that is right next to that chart:
Note that raising the temperature of the 6 min. hold from 1400F to 1700F nearly triples the grain size, from 33 to 94 microns. Like most metallurgy rate processes, grain growth is more sensitive to temperature than time
I strongly recommend further reading in the same book, pages 74 through 76 will clearly describe how substitutional solutes will cause the 5 hour soak with O1 to be entirely possible. The same chapter also goes into the work of R.A. Grange back in 1966 where he shows the refinement of grain to ASTM size 15. Isn't forty years is a long time for something to be ground breaking or theoretical? Mr. Verhoeven also goes on to explain how the same process can be done with no hammering at all.
I could go on for some time quoting how this book entirely supports Phillips findings, or I could point to any number of others. One that I just found on my shelf and had forgotten about is Vanadium Steels and Irons, which explain on every other page how undissolved vanadium carbides will stop grain enlargement.
Finally the chart in question uses 1060 steel. 1060, 1070, 1080, 1084 will all grow grains much more readily than O1, W2, 52100 etc
Without rehashing the other thread entirely, most should see a difference between these steels.
O.K. one more time
Simple iron carbides will take some time to dissolve but will indeed eventually fall to the process of diffusion. Austenite grains form and grow by pulling this carbon into solution. If you are working with a simple carbon eutectoid* steel, or close to it, at room temperature the steel will consist entirely of pearlitic grains with no left over material in the grain boundaries. When you heat this steel the segregated carbon will very easily go back into solution with nothing to stabilize the grain boundaries when it is all used up, so extended soaks with such a steel will produce larger grains over time. However with proper temperature control this is still nothing to worry about.
Steels with stronger carbide formers, vanadium, chromium, tungsten etc
will have plenty of very tenacious carbides that take much more diffusive power to dissolve. In the above mentioned Vanadium book it explains tests done on steels that had vanadium in excess of the necessary carbon levels for proper hardening. Such steels had to be heated to temperatures in excess of 1850F before they would show any hardening from quenching. Why? Because below these temps all the carbon was locked up in V-carbides and could offer nothing to the martensite. You can take it to the bank that there was zero grain growth regardless of how long they soaked that stuff, unless they heated it over 2000F.
To say that it is easier to grow grains when they are finer is inaccurate. All the same rules still apply, just the temperature at which grain boundaries can move gets lower. So if we simply lower our austenitizing temperatures, time once again becomes impotent in comparison. It still all comes down to
control. Folks that have limited precision in controlling temperatures need to worry about grain growth, those who have precise controls have nothing to fear from it and can even soak for ludicrous lengths of time.
We covered a lot of this in Dans question about over soaking his 154CM, there as well we were overlooking the most important part
the temperature, in both cases we are over 300 degrees hotter than you ever go in heat treating simple steels. At these temperatures grain growth will happen when solution is complete.
I hope I never gave the impression that grain growth was impossible from time, it is just not a problem compared to temperature. We don't need a microscope, just put two and two together, if the rate that we are presuming grains to grow in a couple of minutes were applied to 5 hours, we should darn well see those suckers with the naked eye!
I have Phillip's 5 hour O1 in my posession now and I can independantly verify His observations. I have yet to get my tools to precisely measure ASTM grain size worked out from my microscopes to my computer, and Phillips samples are not in a good phase to see grain boundaries, but in comparing it to my samples soaked for only 10 minutes I see no difference is structure size at 400X. I do see some other things however
*Eutectoid: carbon content of approx. .8%
A microscope might reveal more. 
. Perhaps I may find time this weekend. There was a difference in the amount of carbides, but there were still a good number of them there. This tells me that a good area to study now is to see how fine I can make them and where I can put them in the whole scheme of things. A 65HRC as-quenched with loads of very fine carbides evenly scattered throughout the martensite would be very nice.
