Heat treating O1 Steel and grain growth

I get asked quite often about heat treating O1 tool steel. While it is relatively simple in annealed flat section forging brings with it some challenges.
If stock removing from flat bar (or round bar if you hate yourself) heat the O1 after machining to 815 Degrees Celsius and hold for around 10 minutes. Quench into medium speed oil and then consult a tempering diagram.

If forging try to keep the steel between 1065 and 845 Celsius. To correct grain growth I try to follow this schedule:
Heat to 900 and then cool to black heat
Heat to 830 and cool to black heat
Heat to 700 and cool to black heat
To harden soak steel at 815 degrees for 10-30 minutes and quench into medium speed oil.
In the video I show what happens in 2 forged sample pieces. One is quenched too hot with no grain refinement or normalizing. The other follows the formula described above as best I could manage with the camera work. The difference is pretty stark. For a more in depth explanation of the forces at work while forging / heat treating this steel check out these pages https://www.iforgeiron.com/topic/3875...

http://www.cashenblades.com/steel/o1....

To source O1 steel in Australia see this link:
https://www.artisansupplies.com.au/pr...