harden and temper 8670?

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sunnybob

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Jun 25, 2020
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Just about to do this for the first time.
Happy with the high temp of 1525 F, and oil quench.
But unsure on tempering and timings.
Should I temper straight from the oil quench? or wait? or what?

i will be using a domestic oven that goes to 600F (at a pinch). Do I pack the knife in a sand tray? How long at what temps?
Thanks for any help
 
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This is info from Alpha Knife Supply
 
Yes you should temper straight from the oil as soon as it’s down to able to pick it up with bare hands temps in order to lessen retained austenite. Anywhere from 325F for a kitchen knife to 400F for a harder use knife depends on intended use. Two cycles at 2 hours each. I don’t use a sand tray but my oven is pretty stable.
 
Very interesting thanks. Is there a specified time delay between hardening and tempering? Straight off, or next day?
Put the knife in at 250? or bring it up to that temp?
imill3567 said:
Yes you should temper straight from the oil as soon as it’s down to able to pick it up with bare hands temps in order to lessen retained austenite. Anywhere from 325F for a kitchen knife to 400F for a harder use knife depends on intended use. Two cycles at 2 hours each. I don’t use a sand tray but my oven is pretty stable.
Click to expand...

One last question then, time between the two tempering sessions?
This is a largish bowie knife for general outdoor use, I'm thinking 300F going on the chart above?
 
sunnybob said:
Very interesting thanks. Is there a specified time delay between hardening and tempering? Straight off, or next day?
Put the knife in at 250? or bring it up to that temp?


One last question then, time between the two tempering sessions?
This is a largish bowie knife for general outdoor use, I'm thinking 300F going on the chart above?
Click to expand...
To answer your first question, I always preheat to desired temp before putting my blade in. After first cycle, wait for the blade to cool off, then immediately go through your second tempering cycle.
 
Temper immediately and between tempers run it under the faucet to cool off and go right back in oven. Can have it back in the oven tempering again in under a minute
 
That chart from alpha knife supply is wrong for our application and they have said it’s not correct for our use so no idea why they leave it up to confuse people, I’m using a lot of 8670 and for choppers or heavy knives I temper at 375, I like to do my first temper cycle lower than my final number so my first cycle I’ll run it at 300 for 2 hours cool the blade in running water once you pull it out the let the oven come back up to temp at either 350 for small knives or 375 for bigger knives for another 2 hour cycle cooling it with water after I pull them out. If you left a chopper at 300 it would be around 63hrc
 
Oh boy, this is like a sharpening question. i've already got three different systems to choose from.
So, I think this is what I need to do;
Heat to 1560 for 5 minutes.
Quench in oil till hand hot.
Put into a pre heated oven at 300 (1 or 2 hours?)
cool under water.
Temper again at at 350 for (1 or 2 hours?)
Cool under water and polish and edge.
Yes?
 
The ideal temp for when the blade hits the oil is 1525 so bring it up to around 1550 cause it will lose some heat in between your oven and quench tank you don’t need a full 5 minute hold or soak with 8670 2-3 minutes is fine. I use parks 50 to quench and I put the blade in for 7-10 seconds then pull it out to clamp in between plates so nothing warps or moves, let it sit in the plates for a few minutes then go into the pre heated oven to temper once the blade is cool enough to handle. I’d suggest bumping your second cycle to 375 instead of 350 it will give you a bit more toughness for a larger blade and still hold a great edge. I can take a camp knife with a hollow grind and chop through 1/4” brass rods with no edge damage and can cut into mild steel rods without dulling. I’ve made over 60 knives with that exact ht recipe and have had consistent results between them all. It’s a very simple steel to ht and is probably the toughest knife steel you can use.
 
sunnybob said:
Heat to 1560 for 5 minutes.
Quench in oil till hand hot.
Click to expand...
Larrin's book recommends 1,525F for 10 minutes, quench in medium/fast oil.

This is how I heat treat:
1. Preheat furnace to temperature and let it sit at temperature for 30 minutes to an hour.
2. Put blade in and wait until it comes up to temperature.
3. Start a timer for the recommended soak time.
4. When timer goes off, quench for 10 seconds.
5. Immediately put the blade between aluminum quench plates in a vise to keep the blade straight.
 
Joshua Fisher said:
The ideal temp for when the blade hits the oil is 1525 so bring it up to around 1550 cause it will lose some heat in between your oven and quench tank you don’t need a full 5 minute hold or soak with 8670 2-3 minutes is fine. I use parks 50 to quench and I put the blade in for 7-10 seconds then pull it out to clamp in between plates so nothing warps or moves, let it sit in the plates for a few minutes then go into the pre heated oven to temper once the blade is cool enough to handle. I’d suggest bumping your second cycle to 375 instead of 350 it will give you a bit more toughness for a larger blade and still hold a great edge. I can take a camp knife with a hollow grind and chop through 1/4” brass rods with no edge damage and can cut into mild steel rods without dulling. I’ve made over 60 knives with that exact ht recipe and have had consistent results between them all. It’s a very simple steel to ht and is probably the toughest knife steel you can use.
Click to expand...
The temperature that matters is where it soaks not the temperature at which it hits the oil. Unless it cools off so much it begins to form pearlite of course.
 
Larrin said:
The temperature that matters is where it soaks not the temperature at which it hits the oil. Unless it cools off so much it begins to form pearlite of course.
Click to expand...
That’s good to know, So in this case it would be best then to just bring the temp up to 1525 and hold there then go straight into the quench
 
I normally soak at 1575 for 5 minutes, quench in Parks 50, and then temper for two 2 hour cycles at anywhere between 350F to 400F. After my first temper, I'll just dunk it in a water bucket to cool to room temp, and then pop it right back in the oven. So far I've been very happy with the results.
 
I would agree with everyone saying higher temper than 300F for a Bowie. I use 8670 quite a bit and I’d agree 375-400F for this application. I also use 1525F since I go off Larrin’s research.
 
This is going to be a bit hit and miss. I have no dedicated equipment. I'm going to use large clay air bricks as a forge, and a MAPP gas torch for heat. I do have a digital thermometer that will reach those temps though.
I'll do my best.
Thanks for all the advice.
imill3567 said:
I would agree with everyone saying higher temper than 300F for a Bowie. I use 8670 quite a bit and I’d agree 375-400F for this application. I also use 1525F since I go off Larrin’s research.
Click to expand...


I've hit a major snag. My home made forge just isnt good enough to heat to the required temps. I cant get it above 600c (1100F).
I'm on a fixed income and spending a lot on this is not an option. So is it possible to just heat the cutting edge rather than the whole blade? This knife is just a fun project to see if I can make a knife, I have no real need for it, so as long as it doesnt bend when chopping a piece of wood I will be happy to have it as just a wall hanger.
 
Can you tell us a bit about your forge? Photos would help, too. Also, how are you determining the temperature of the steel in the forge?
 
Its not a forge in any real sense. I have no equipment suitable.
I have several large clay building blocks that I put together loosely, leaving only enough space for the blade. But I only have one MAPP blowtorch.
I have a handheld digital thermometer that will reach a 1000c with a metal probe. I got the temp up to 600c, but without a second mapp torch i just cant get the last step of the way.
I have no extra cash to spend on this experiment, if I cant get the whole blade to 830c then my only other options are to either edge quench, or just leave it as a soft wall hanger / conversation piece.
 
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