80crv2 chopper: heat treat aspects

Normalizing temperatures allow for all of the carbides to be dissolved and precipitate back as fine spheroidite or fine pearlite.

To achieve fine spheroidite in simple or low alloy steels, oil quench from normalizing temps. To get fine pearlite for the same steels, air cool.

After developing fine spheroidite, sub-critical anneal and then move to the austenitize, quench and temper.

After fine pearlite, refine the grain by cycling at lower temps, then austenitize, quench and temper.

Hoss
 
Thank you all for the education !
I should have been more specific
1- the 80crv2 steel I am using most likely has large spheroids
2- I am using stock removal for a large chopper 10 inch blade 1/4 inch thick
3- I have a sigital kiln that is pretty accurate

What would be the recommended heat treat for this tupe if knife
 
Large/coarse spheroids suck to start a heat treating regime from if you don't forge.

Do you have a forge... or just the kiln?

Start at 1650F-1700F for your initial normalizing cycle.
 
Rick Marchand said:
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.

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.

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.
Click to expand...
Could he use tempil sticks? just curious
 
1huckstir said:
Could he use tempil sticks? just curious
Click to expand...
Once you have experience with them, maybe. I found them very difficult to carry over to knifemaking. You can't use them in the forge or kiln and once you pull the blade out, the temp is starting to drop pretty quick. I gave up trying to make them work, but other's use them.
 
I think the idea of descending temps for thermal cycling likely became so prevalent because of simple equipment with some lack of any real control. Sort of like an insurance policy, erring on the side of low end, when smiths weren't exactly sure of temps.

If you have a reliable way to know for sure what your target temp is and that you're not overheating, there should be no reason that 2 or 3 thermal cycles from, say 1475, shouldn't be just as effective as 1475, then 1450, then 1425, etc.
 
You must log in or register to reply here.
Back
Top