I do not have high precision insturments to measure temperature. The temp of my quench tank is measured by the same thermometer I have used for over 30 years. Is its 165 f. actually 165 f or maybe a little different. It does not matter, it is the same each time. I evaluate the results by performance not the recorded temp. This may be a simple explanation, but this is how I work.
I use my Paragon to soak billets at critical temp. I coach the temp up until the steel just looses its magnetism. I look at the stated temp on the read out and record what it says. It does not matter if the thermal couple is absolutely accurate, the magnet provides the information we need. The temp predicted by the thermal couple is simply a number for me, a reference point that is the same and I know it is the same by the nature of the steel at that reference point. That is all that matters, the alloy may or may not become nonmagnetic at the exact temp in reference books, I know where I am by the magnet and that is all that matters to me.
At one time I had a friend shoot temps of blades we were quenching using a recently calibrated optical pyrometer. According to it, critical temp seemed to vary when other variables were manipulated. We worried about it for some time, then came to the decision that the exact temp did not matter all we needed to knwo was the point when the magnet said the steel was hot enough (in this case critical temp).
Some experimental blades seem to drop down through critical at different rates when doing what I call the bladesmith flash normalize. We have fooled around with a stop watch to check this theory out and have not reached a definate conclusion. In reality it does not matter, heat uniformly to critical, verify with a magnet and watch it cycle down. Again the actual temp and time down does not matter, it is the cycle that is significant.
I do believe that temperatures and heat times (conductivity) may vary with grain refinement, can I prove it? No. Does it matter? Not really.
We could spend some money on instruments that could shed some light on these questions, but is it worth it? Maybe to some and the questions and answers may be of value to someone in another application.
At this time we are working on reduction ratios and the influence of higher temperatures at the start of reducing steel by forging. This is kind of interesting because we will know how far a bladesmith can push this steel starting from a billet of smaller volume.
You mentioned full hardening, I believe several extensive volumes could be written seeking a comprehensive evaluation of full hardening, add what for to the question and another lifetime could provide another answer or two.
Anyone who in interested in working with these variables is welcome to join and work with us. I sincerely appreciate your questioning what I said, there is a lot to learn, this is why we will never know it all. (I hope)
