1- why is 1530 to high for aust?
It isn't "too" high. but it is on the high end of the spectrum, especially when soaking. What we did in those initial cycles to refine grain and distribute carbides can be undone with high heat at extended soak times. If your last cycle was at 1450F and you did your best to "lock it in", I would not want to push my luck.
2- for normalizing I have heard peoplr use three temperatures 50 above aust, aust and 50 below aust... does that make sense?
It doesn't... Ha!... I'll try to explain it the way I interpret egg-heads like Cashen, Mete and Larrin... no offence, Nerds. Maybe my dumbereded version sings to someone. Hopefully, it isn't too far gone to be useful. Let me know if there is any treacherous metallurgical misinformation.
Austenitizing temperature is a "phase" not a set temperature. Once you get above critical, you are austeniting. Normalizing is just that... making everything even and normal. That happens with your first high heat at 1650F or so. You are breaking up carbides and growing the grain evenly across the structure. The subsequent heats are refining the grain and referred to as "thermal cycling", not normalizing... but folks know what you mean when you simply call it all normalizing.
You use descending heats so you don't undo what you've accomplished in the previous cycle. I choose to quench on the last cycle because I feel that working from fine martensite with good carbide distribution is better than a mixed structure with possible segregation and other not so fun stuff. The last dull red heats are kind of a redneck spheroidizing/subcritical anneal. It creates fine spheroids and makes the steel easier to machine, grind and drill. Some steels need this to be done at exact temperature for extended soaks and cooling rates, 80CrV2 is fairly straight forward.
3- during normalizing is it necessary to quench in water after all heats ?
No. When thermal cycling, you only need to have the steel go from austenite to "another phase". When the steel becomes magnetic again, you've accomplished that and can ramp back up to the next heat. Only on your final heat do you want to mess with the cooling. As I explained above, I quench to martensite. Some don't and that is okay, but you don't want it to run away on you. As it cools naturally, austenite transforms to coarse pearlite, pearlite and fine perlite... if slowed even further, it forms other stuff that I won't get into. Fine pearlite is stronger than coarse and more difficult to machine/drill, so essentially we are avoiding the fine stuff(and other nasties) by quenching in water/oil once it gets below 900F or so.
*** I have to ask this***
What are you using as a heat source? All this talk of 1450F, 1530F, 5 minute soaks and such are for nothing if you are using an open forge without a PID. YOU CANNOT "EYEBALL" EXACT TEMPERATURES. There are ways to do it in an open forge but don't fool yourself into thinking you can hold for 5 minutes at 1530F, by eye.
These are my conclusions, based on the info I have gathered, thus far. Other folks may do it differently and i'd happily change my ways if I felt it would improve my own method.
That's how this Caveman sees it.
