I found this video informative.
Ken
https://youtu.be/G3B3K3QTRHc?si=qwCtImYyYD9PRTVl
Best description of hardening and tempering and why that I've ever read/heard (not that I have much of either).
Saw this James is one of my favourite woodworking educators. Having said that it is a thinly disguised advert for Narex, but he is up front about it, unlike many others! I have a set of those Narex Richters and absolutely love them. The best value for money for the harder steel chisels. The Diamond wheels are invaluable for sharpening them due to the high MOHS hardness.
Great video and well explained.