Austenitizing is the last thing to do in simple martensitic steels (all of them for us as far as making woodworking tools). Austenitizing does a couple of things:
1) it changes steel to a nonmagnetic phase. there are lot of explanations here about body centered cubic and face centered, but you can't see steel like that, so I'd like to avoid it.
2) it does a combination of things on top of that - from getting some alloying elements or additional carbon in solution to different temperatures having some effect on how fast steel needs to transition in the first part of the quench so that a soft formation of pearlite invades the steel.
Once your heat is what you want, you immediately go into the quench. I'll describe quenching in a separate post. there are some things you want to do when quenching and some you don't want to do.
there may be more to austenitizing than 1 and 2 above, but I haven't been forced to learn what they are to make good tools. you can read more about what happens, but if you're working hand and eye, avoid taking interpretations about what happens in a furnace in 20 minutes and imagining that you have problems that you don't actually have.
In an electric furnace, there is a prescribed temperature for the soak and usually a range of times. For simple steels near the eutectoid limit (beyond which surplus carbon is available), little needs to happen other than thorough heating to nonmagnetic and then getting the steel to the quench quickly. When you heat treat O1 or 52100, or some other steels with excess carbon like 26c3 or a 1% W1 steel, getting to nonmagnetic only or just barely over will often or in some cases, always, result in underhardening and undesirable aspects for tool performance. the dynamic here is among all steels, all of these are relatively simple. Among simple steels, 52100 is a lot different than 1084 or 1095, and O1 is to some extent, too, though O1 is more forgiving if chasing full hardness than is 52100.
You can take a clue from furnace schedules as to what you have to do, and see the comment on sample snapping to find out how to test if what you're doing is causing grain enlargement. There is never a case that I can think of where we'd want grain enlargement, but it can give a false sense of success because larger grains frozen in place during the quench are also correlated with high hardness or high hardness results.
We want the highest reasonable hardness out of the quench, without any grain enlargement.
to observe the furnace issue here - this is new jersey steel baron's heat treat sheet.
https://newjerseysteelbaron.com/wp-content/uploads/2020/10/1084-Heat-Treat-7-20.pdf
Note, the austenitizing temperature after the thermal cycles is 1450 to 1480F and the soak time isn't particularly long in a furnace- as little as 5 minutes. (ignore their thermal cycle starting at 1650 - that's kind of a do all for them and I'd imagine it grows grain - it's there on 1084 and there on 52100 and so on. I'll bet larrin has said something about it before)
The 1450 starting heat range and short soak should tip you off that the steel doesn't need much heat past nonmagnetic and it doesn't need a soak to get anything in solution. And this often also signifies that there's nothing to stop grain growth and you'll see a lot of it if you start pushing heat higher - and that is the case for 1084. grain growth is swift and that's a bad thing if you're causing it.
The generalized method working hand and eye is to get to nonmagnetic, and then for a matter of ten seconds or so, get to a higher temperature and then quench. The answer from experience for 1084 is that this "how much hotter" is "only a very small amount". Snapping samples will confirm things for you, and if you bloat a sample, then you have an opportunity to prove you can "unbloat it" with thermal cycles.
Let's compare what they say about O-1:
https://cdn.newjerseysteelbaron.com/wp-content/uploads/2020/07/O-1-Heat-Treat-7-20.pdf
Well, that's disappointing, actually - the same temperature but double the hold time or more. There's some learning opportunity here - O1 has a range of oven austenitizing temperatures. 1084 doesn't really have much range due to the fast grain growth. The reason being that there's more to get into solution in O1 and more stuff in O1 that can restrict grain growth. So, let's check another heat treat routine - one probably guided by larrin, but also in agreement with bohler's sheet:
https://www.alphaknifesupply.com/shop/o1-carbon-steel
the upper limit for the soak is 1510F, which doesn't sound much different than the 1450-1480 with a short soak, but there's a world of difference here when the range is increased and the soak time is doubled. This difference usually signifies you need to push the end of the heat ramp up higher and you have more room to do it.
So what does this mean for you when actually hardening. The 10 second very slight heat increase with 1084 before quenching won't be ideal for O1. For O1, the 10 seconds is fine, but you need to push the visual a full color shade. As in, when magnetism leaves at what you perceive to be a mid red, you need to get O1 to mid orange in 10 or maybe 15 seconds and then quench.
if you dawdle and continue to go too hot or too long, you'll enlarge grain, but there is a lot of forgiveness here, and if you quench after just getting to nonmagnetic or a little past, you're going to end up with something that would've been more suitable for knives.
this sounds taxing, but it's actually what makes this process easy. What you use is going to create some boundaries that you have to operate in. All you have to do is snap a few samples and test a tool or two and you'll find something good quickly, and you can write it down and just do it. In a strong local heat propane forge, for me, that with O1 was one color change in about 15 seconds after hitting nonmagnetic and quench. Induction forges take a little bit more color change than that to be all they can be (and without any grain growth) because the jump in temperature may take 3 seconds instead of 10 or 15.
You don't need to get good at 10 steels. You may only need to figure out one. My suggestion for you if you're new is that steel should be O1. You can ignore the advice from knife folks about how hard it is to heat treat O1, I think they're getting confused with how hard it is to forge it if you're coming from a simpler steel and encountering cracking problems due to O1 partially hardening as it cools. they'll have nothing to do with your efforts just heat treating. you can branch out after that, but I can't think of any cold work tool where O1 would actually fail to make a good tool, and the fact that it hardens fully at a slower cooling rate than water hardening steels means you can use any decent vegetable oil to quench it and get good results.
Vegetable oils don't flame up as much as fast oils like parks 50, and they smell like food when you temper an iron. Parks 50 smells like burning paraffin oil. OK for single men, but not something a spouse or kids will be quiet about.