Here is how I see this issue. One steel vendor sells steel that is coarsely spheroidized. This steel is extremely soft, softer than it needs to be for most of us, but guys who use CNC may really really like the benefit of it being super soft. However, if one were doing stock removal only, and went to harden it (without normalizing regimen...using the standard single quench....like we would heat treat O1 received from Sheffield for example), the resulting hardness would be around 63HRC, about 4 or 5 points lower than it "should" be. How will you know if you achieved 67HRC without a Rockwell tester? Some files would skate on 63-64. And if you were to break the sample to check grain size...it could be extremely fine. But you're 4 points lower than you should be. Hence, the normalizing routine to break up the carbide networks and free up the carbon, to achieve what we're after....66-67HRC+. This adds time/energy to the product. The normalizing heat takes care of carbide structure, but at the possible expense of aus grain size, so we usually thermal cycle a few times to take care of the aus grain. That's usually 4 or more cycles added to a hardening operation.
The other steel vendor sells the same steel/steels, but he orders them fine spheroidized. It's soft enough to grind, soft enough to file, but maybe not QUITE as easy on tooling as coarse spheroidized. Maybe it is 22HRC instead of 19HRC (total guess here). But this steel is ready to harden as received. No need for normalizing/cycling. It reaches max hardness out of quench with the standard heat treat (heat, soak, quench, temper). One hardening operation without the normalizing and subsequent aus grain refining.
However, we as knife makers should be aware of how to work the steels we receive. Glad to see this thread.
