Ok I know that there is somewhere I can find this info but I am either not using the right key words to search it and I've been searching here and google for about three hours now, so please do not just reply "use the search bar". You don't have to give me a detailed explanation if you know there is a link to the info or know which keywords to use for searching that will suffice (links to reliable sources being preferred)
Anyways the question is, when tempering hardened steel, why do different temperatures affect hardness. Like what is happening molecularly or whatever that makes it softer but tougher at say 400 degrees whereas 300 will be harder but more brittle (temperature numbers just given as examples). What voodoo is going on that when tempering at 300 the hrc value only drops a point or so but at just 100 degrees more it drops 5 points and so on. Also does time play a huge factor. Example, let's say I take a knife of O1 at 65 hrc quenched and double temper it at 450 and I take another identical knife and temper it at 450 for 12 hours. Would there be a difference in hardness or toughness towards one or the other. I read somewhere that if you leave steel to temper at a temperature that would leave a straw color, if tempered at two hours, normally and left it in there longer it can turn a color that would resemble as if you were to temper it at a higher temp, say blue, but it didn't say if this actually reflected a change in the hardness as well.
Also, embrittlement tempering range. If I understand this right it is the temperature at which a particular steel will get softer but also more brittle. What is this temperature for say O1 and 440 series stainless as those are the two steels I use mainly besides sometimes (read rarely) ats 34.
I really appreciate any insight you can offer. I know it's a long read and I apologize if it has been asked before and could have searched it. I tried to search it but couldn't really find anything other than "tempering at 300 will give you a harder blade than tempering at 500" kind of answers. I know that but I want to know the why. Thanks again for any help.