8670 heat treat coupon results

[Willie71]

i posted this in the other thread on 15n20 vs 8670, and here are the results:

8670 numbers are in, and I’m getting consistent Rc64/65 with austenitizing temps between 1525 and 1600. Going to 1475 starts dropping to the Rc62/63 Range, and going to 1625f or 1650f starts dropping to Rc60/62. 1475f still got Rc65 on a couple readings, but there were some Rc61/62 readings as well. 1500f got the Rc64/65 numbers but there were a couple of Rc62 readings.

So, in summary, I would use 1525-1575f for most consistent results. I only got one reading at Rc66, and that was at 1525f. You basically have a very forgiving steel that will get good results over a 100f Range. With a kiln, set it at 1525f, and go.

Edit: I used DT48 to quench. I’ll try heated canola when the inlaws leave and see if it makes a difference.

 

[DevinT]

Dude, you are a testing machine.

Hoss

 

[Willie71]

Dude, you are a testing machine.

Hoss

This is the most important part of knifemaking. We have to get this part right.

 

[Willie71]

I’ll use 1525f for the Charpy samples for Larrin.

 

[rodriguez7]

I’ll use 1525f for the Charpy samples for Larrin.

That’s what I’ve been getting good results with. But I’m using parks 50, have you tried it? Curious what the difference is.

 

[DeadboxHero]

i posted this in the other thread on 15n20 vs 8670, and here are the results:

8670 numbers are in, and I’m getting consistent Rc64/65 with austenitizing temps between 1525 and 1600. Going to 1475 starts dropping to the Rc62/63 Range, and going to 1625f or 1650f starts dropping to Rc60/62. 1475f still got Rc65 on a couple readings, but there were some Rc61/62 readings as well. 1500f got the Rc64/65 numbers but there were a couple of Rc62 readings.

So, in summary, I would use 1525-1575f for most consistent results. I only got one reading at Rc66, and that was at 1525f. You basically have a very forgiving steel that will get good results over a 100f Range. With a kiln, set it at 1525f, and go.

Edit: I used DT48 to quench. I’ll try heated canola when the inlaws leave and see if it makes a difference.

Thanks brother, big help

 

[Ian Fifelski]

Thank you for this. I have always wondered why there seemed 100 different ways to do the same thing with heat treating.. Why does something scientific seem to be a matter of opinion.
Good to see a simple "With a kiln, set it at 1525f, and go." I am writing this down.

 

[Willie71]

That’s what I’ve been getting good results with. But I’m using parks 50, have you tried it? Curious what the difference is.

Parks 50 and DT-48 are pretty much interchangeable. I mentioned this in the other thread, but thought I would confirm it here too.

 

[samuraistuart]

Thanks, Warren. Mirrors what I'm getting with 1525f and canola.

 

[Willie71]

Thanks, Warren. Mirrors what I'm getting with 1525f and canola.

My canola is stale. I’ll try my medium oil to see if there is a drop in hardness. I doubt there will be.

 

[jdm61]

With deeper hardening steels, you can run into trouble with thin blades using Parks #50 just like you can with water on shallow hardening steels.

 

[Willie71]

With deeper hardening steels, you can run into trouble with thin blades using Parks #50 just like you can with water on shallow hardening steels.

Interesting that you mention it. I was thinking I should use medium speed oil for the Charpy samples to control for quench stress.

 

[DeadboxHero]

Here a question, is it worth it to spend the extra money on AAA medium quench oil or is there no REAL difference between that and canola at 120f?

 

[Willie71]

Here a question, is it worth it to spend the extra money on AAA medium quench oil or is there no REAL difference between that and canola at 120f?

I wondered the same, and I don’t know the answer, beyond the fact that canola will go rancid over time.

 

[samuraistuart]

Take this with a grain of salt, but I "think" the advantage that commercial oils have over a straight vegetable oil is that they are formulated to slow the cooling rate in that 900f-ambient range and also they are formulated to last. Canola is a decently fast oil, it will harden many steels just fine (even the shallow hardening ones in thin cross sections), but doesn't last as long, and probably isn't as gentle in that period of martensite start temp range (which hasn't presented me any problems).

 

[jdm61]

That is my understanding. We talk about 7 second or 13 second oil, but not much about what the cooling curve looks like.

Take this with a grain of salt, but I "think" the advantage that commercial oils have over a straight vegetable oil is that they are formulated to slow the cooling rate in that 900f-ambient range and also they are formulated to last. Canola is a decently fast oil, it will harden many steels just fine (even the shallow hardening ones in thin cross sections), but doesn't last as long, and probably isn't as gentle in that period of martensite start temp range (which hasn't presented me any problems).

 

[jdm61]

I don't if canola has the "sweet spot" that AAA and the Houghton equivalent have. They say 11-13 second because it is 11 second at like 150F but 13 at say 120 or 180.

 

[Larrin]

Physics dictates that cooling rates are slower at lower temperatures. I don’t think the quench oil manufacturers are good enough to get around physics. https://en.m.wikipedia.org/wiki/Newton's_law_of_cooling

 

[Kyle Jones]

i posted this in the other thread on 15n20 vs 8670, and here are the results:

8670 numbers are in, and I’m getting consistent Rc64/65 with austenitizing temps between 1525 and 1600. Going to 1475 starts dropping to the Rc62/63 Range, and going to 1625f or 1650f starts dropping to Rc60/62. 1475f still got Rc65 on a couple readings, but there were some Rc61/62 readings as well. 1500f got the Rc64/65 numbers but there were a couple of Rc62 readings.

So, in summary, I would use 1525-1575f for most consistent results. I only got one reading at Rc66, and that was at 1525f. You basically have a very forgiving steel that will get good results over a 100f Range. With a kiln, set it at 1525f, and go.

Edit: I used DT48 to quench. I’ll try heated canola when the inlaws leave and see if it makes a difference.

Warren,

I like using the 8670, but I'm puzzled by either the numbers you're getting or what AKS has on their site for heat treating results. They're chart isn't getting anything near what you are. What's the deal with that?

I can't post the picture of the chart, but as quenched at 1600 puts the HRC at barely over 61, then descends rapidly with tempering. Do you think I should ask Chuck where they are getting the info? I'll bet the manufacturer's chart was intended for something other than "knife" blades.

Thanks in advance!

 

[samuraistuart]

Kyle, I can almost guarantee that is the case. Those charts are industry charts or something to that effect. Take a look at their 52100 HT info. The guys here on this forum (and many that aren't here any longer) figured out how to HT 52100, and that chart is WAY off. 1545-1615 is just way too hot for heat treating a knife in 52100. A bearing would do OK with that HT, but not a fine, thin edge. Their charts are off, but their steel is excellent.