I was limiting the discussion. I guess I was asking about the differences between this sample of 52100 at 61hrc and another sample at the same hardness made by a different maker.
That was exactly what I was looking for. So basically two identical pieces of steel that are heat treated to the same hrc will still have different performance based on the amount of time they spend in the "oven"....?.
Also if there is a 2-3min. window where there are both austenites and martensites and austenites are bad why not wait 4 minutes so you only get martensites?
There is a number of factors. For every steel there is a range of temperatures it could be heat treated (austenitizing and tempering), and the outcome will depend on those temperatures, time soaked at that temperature, speed of cooling, cryo treatment and other steps.
I am just going to run a two hypothetical cases scenario. To simplify things, I will take cryo out of the equation and in both cases steel is soaked during austenitising and tempering same amount of time.
Scenario #1
If you heat treat at close to the lower temperature in the range, you get smaller grain size (more toughness, easier to sharpen) but wear resistance will suffer, as at the lower temp you get less of the components dissolved into a steel matrix. Nonetheless, say you get 64RC as quenched. You temper at a certain temperature, 2 sessions 1 hour each, and the end result is 61RC. Totally doable.
Scenario #2
If you heat treat at close to the upper temperature in the range, you get a larger grain size (less toughness, more wear resistance). Say, as quenched you get 66RC. You raise your tempering temperature, and do 2 sessions of tempering and the end result is 61RC.
First one will perform very differently than the second one - it will be easier to sharpen, and will have very stable edge. Second will have more wear resistance, but might be prone to chipping.
What I described is the window
after the quench, while the transformation is still occurring. Certain steps in custom heat treatment allow to reduce retained austenites to the minimum (if not zero). You will know that by increased hardness of your heat treated blanks and ease of sharpening - burr will raise very evenly and will be easy to remove. There is a reason why commercial HT blades are in the 60-61RC range, as when you heat treat a large batch there is a time lag between processes, and that short window of opportunity is missed. For instance, cryo treatment the next day makes no difference on the steel whatsoever.
Hope this makes sense.
A good place to read about this stuff is Devin's subforum and website.
M