CPM154 cryo, temper, heat treat questions

cotdt said:
What are the disadvantages? I'm very interested in hearing your thoughts on this.

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The down side is it lowers edge stability and reduces corrosion resistance. It creates a larger carbide volume at the expense of a more carbon lean martensite and less free chrome.
 
Yup - readers digest version anyhow. Other details like double foil wrap - paper in envelope to eat what little oxygen there is - hardness test every blade (where possible) before it is sent back... Obviously those temps are just for D2. Many of our recipes are posted on the Evenheat site as well. Of course, we are glad to make any changes the customer asks for.

Rob!
 
Regarding the high tempering temperatures for CPM 154, I also talked to Paul about this and he said the reduction is corrosion resistance is only a few percentage points. Does that mean anything? Maybe, depending on if you clean your knife after you use it. As far as the toughness, it also increases the toughness of the steel by a few percentage points. I don't know how much grain growth is a problem with CPM technology, but I have ground and finished half a dozen blades that were tempered at 900F. The blades didn't show any visible carbides and took a mirror finish on the edge quite well. They Rockwelled at 61 and I have abused the hell out of one of them and it is still razor sharp with no edge defects. So, I don't know that it is a bad thing from my experience. Paul told me that Mr. Loveless has his blades tempered around this temp and I know for a fact Jerry Hossom does too and both gentleman's knives speak for themselves.
-John
 
I want to confirm that toughness in knifemaking terms is really impact toughness of the edge or tip. Examples would be chopping or batoning through wood or stabbing something that is fairly hard.

Does the ability to hold a very thin edge and not be too brittle and chip out while slicing soft to medium materials fall under "toughness"?
 
gshamr said:
I want to confirm that toughness in knifemaking terms is really impact toughness of the edge or tip. Examples would be chopping or batoning through wood or stabbing something that is fairly hard.

Does the ability to hold a very thin edge and not be too brittle and chip out while slicing soft to medium materials fall under "toughness"?
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People use the term edge stability for that. Toughness usually refers to "through the grain" toughness, like Charpy/Izod impact tests. Copper is extremely tough, but won't hold a thin edge well. You need hardness to support a thin edge.
 
Barker said:
Regarding the high tempering temperatures for CPM 154, I also talked to Paul about this and he said the reduction is corrosion resistance is only a few percentage points. Does that mean anything? Maybe, depending on if you clean your knife after you use it. As far as the toughness, it also increases the toughness of the steel by a few percentage points. I don't know how much grain growth is a problem with CPM technology, but I have ground and finished half a dozen blades that were tempered at 900F. The blades didn't show any visible carbides and took a mirror finish on the edge quite well. They Rockwelled at 61 and I have abused the hell out of one of them and it is still razor sharp with no edge defects. So, I don't know that it is a bad thing from my experience. Paul told me that Mr. Loveless has his blades tempered around this temp and I know for a fact Jerry Hossom does too and both gentleman's knives speak for themselves.
-John
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The decrease in corrosion resistance is enough to worry about, if it's still good enough for you that's fine. I have never seen a test that showed that a knife was tougher after a high temperature temper. I would be worried if my knives showed visible carbides, that shouldn't be changed by an upper temper. The performance of one knife is almost meaningless without a comparison to another.
 
Larrin said:
I have never seen a test that showed that a knife was tougher after a high temperature temper.
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I agree. From Crucible's CPM154 Spec sheet:

Note: As with all martensitic stainless steels, tempering at 800-
1100°F (425-600°C) will result in sensitization which causes a
minor reduction in both corrosion resistance and toughness.​
We recommend that this tempering range be avoided.

Having said that, with the number of well respected makers (and manufacturers) using both, I suspect the difference can't be much.

We use the low range by default because Crucible recommends it. If a customer wants the high temp quench , he sure has respected backing, so we are glad to comply. :)

Rob!
 
I'm fascinated with Dozier's heat treat--probably because of a mixture of being fascinated with anything that's "secret" and that I love his design sense. I just found this thread and wanted to add two observations from the recent youtube video in his shop (http://www.youtube.com/watch?v=YGGwQnDXExM&feature=plcp). First, Dozier heat treats using a pre-heated oven. He's adding the knife at what looks like between 1000 and 1400 degrees (I'm guessing this based on the glow of the oven compared to my own Evenheat at known temperatures). There's a data sheet from one of the steel manufacturers suggesting something similar for D2--I don't remember which manufacturer recommends using a pre-hot oven, but they were the only one out of 4 or 5 that did so. Secondly, the post-heat treat blade shown in the video is very dark. When I've heat treated D2 (1850, 45 min, plate quench, 2x 2 hrs at 450), it doesn't color nearly as much as the almost black-purple blade that they ended up with. It looks much closer to the post-heat treat knives that were tempered at 900 degrees. This causes me to suspect that Dozier is in fact tempering at the 2nd hump. Nathan, you mentioned 'non-benefits' of tempering D2 in that range. What have you found them to be?

The youtube vid is definitely worth watching.
 
Try water quenching after the first and second tempers, this also helps with converting Ra.

Chilled plates, cryo/subzero, and water quenching after tempers all help with Ra
 
PatrickBarter said:
I'm fascinated with Dozier's heat treat--probably because of a mixture of being fascinated with anything that's "secret" and that I love his design sense. I just found this thread and wanted to add two observations from the recent youtube video in his shop (http://www.youtube.com/watch?v=YGGwQnDXExM&feature=plcp). First, Dozier heat treats using a pre-heated oven. He's adding the knife at what looks like between 1000 and 1400 degrees (I'm guessing this based on the glow of the oven compared to my own Evenheat at known temperatures). There's a data sheet from one of the steel manufacturers suggesting something similar for D2--I don't remember which manufacturer recommends using a pre-hot oven, but they were the only one out of 4 or 5 that did so. Secondly, the post-heat treat blade shown in the video is very dark. When I've heat treated D2 (1850, 45 min, plate quench, 2x 2 hrs at 450), it doesn't color nearly as much as the almost black-purple blade that they ended up with. It looks much closer to the post-heat treat knives that were tempered at 900 degrees. This causes me to suspect that Dozier is in fact tempering at the 2nd hump. Nathan, you mentioned 'non-benefits' of tempering D2 in that range. What have you found them to be?
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The down side is it lowers edge stability and reduces corrosion resistance. It creates a larger carbide volume at the expense of carbon lean martensite and reduced free chrome.

In D2 the secondary hardening hump increases certain kinds of abrasion resistance, impact resistance and dimensional stability. All excellent things in a stamping die (what D2 was originally designed for), however, in a knife edge you will see reduced edge stability due to lower edge strength (carbon lean martensite is weaker) and an increase in chippyness (is that a word?) due to a larger carbide fraction in a softer matrix. And lower corrosion resistance due to free chrome being consumed in carbide formation. An edge in D2 does better if you leave the carbon in the martensite. Thus the only benefit to the secondary hardening hump in a knife edge is the elimination of retained austenite. However, quenching to Mf without delay also eliminates RA.

I don't think Dozier uses the secondary hardening hump. He told me once that his heat treat reduces D2's tendency to rust, which tells me he has plenty of free chrome in there. You don't get that with the secondary hardening hump.

He has a good HT and he is very secretive about it. He doesn't use cryo, though quenching to Mf (approximately -100f) isn't cryo. However, as good as his HT is, I have tested other D2 blades that equal it in realistic cutting tests, so he isn't doing anything magic beyond performing a competent, high quality HT well tailored to the application. Which is pretty much what he has always said. It just seems so much better than "other D2" because so many people have been tempering when warm to the touch and either going to the hump or neglecting the RA, so in comparison, his work is much better than the mediocre D2 that is so common.

He told me he isn't doing anything that you can't read about in industry texts, which pretty much jives with my testing of his work and other quality D2 knives.

I think the blade coming out of HT is dark because of the austenitization heat, which would have nothing to do with the tempering temperature. Some people put stuff in the pouch to absorb oxygen that turns their blades dark like that.
 
chad2 said:
Try water quenching after the first and second tempers, this also helps with converting Ra.

Chilled plates, cryo/subzero, and water quenching after tempers all help with Ra
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True. A more rapid quench reduces carbon migration, which in turn will maximize strain energy at the end of the quench. Strain energy is behind the mechanism in converting RA.

Water quench out of temper is not a harmful shock and reduces precipitation of carbides responsible for cold embrittlement.
 
Great info guys! Thank you for sharing. Now Nathan, you've posted about water cooled patens before... ever think of chilling quench plates that way? How about a chilled quench plate press? Sounds like fun with the right juice running through them!
 
I think a chilled quench plate would be only useful for those doing production runs, and needing the plates to stay cool, and not heat up as multiple blades are quenched.

In the average shop, it is probably unnecessary. Comparing a chilled quench plate to standard 2-3" thick aluminum plates is like comparing a 400 pound anvil to a 300 pound anvil. Is it better - sure! Is it going to make any difference to the average maker - Nope!
 
Does it hurt to know the info? If you want the very best, you should do the very best even if the results will never effect the customer.
 
I was imagining plates that could be cooled to well below "cool". Imagine a plate quench system that could quench as a normal plate quench works...down to room temperature, but then take advantage of the available-to-convert RA and immediately flush the plates with some -30 coolant that's been run through a dry ice slush bath.

Very speculative, but it seems like that'd be a pretty efficient and possibly effective way to get a really good quench and avoid doing a whole extra cryo step in some cases. The quench plate device would be pretty complicated, though. I'm sure there's a lot that will go wrong with pumping that temperature liquid around.

Chad2, I dig the sentiment. Best results possible or bust. Each step should be free of fuss and guesswork.

But until then, I should really get some thicker plates. Mine are 1/2" thick and I got them years ago before I'd thought about the possibility of doing more than 1 or 2 blades at a time.
 
PatrickBarter said:
I was imagining plates that could be cooled to well below "cool". Imagine a plate quench system that could quench as a normal plate quench works...down to room temperature, but then take advantage of the available-to-convert RA and immediately flush the plates with some -30 coolant that's been run through a dry ice slush bath.

Very speculative, but it seems like that'd be a pretty efficient and possibly effective way to get a really good quench and avoid doing a whole extra cryo step in some cases. The quench plate device would be pretty complicated, though. I'm sure there's a lot that will go wrong with pumping that temperature liquid around.

Chad2, I dig the sentiment. Best results possible or bust. Each step should be free of fuss and guesswork.

But until then, I should really get some thicker plates. Mine are 1/2" thick and I got them years ago before I'd thought about the possibility of doing more than 1 or 2 blades at a time.
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In your situation it will actually benefit you more to chill your plates. Because they will stay cooler long. The minimum requirment for plate thickness is 1" and that is becasue you have enough material to handle high heats for 30 secs or more. Now for you throw your plates into the fridge about 15 mins before your knife comes out of the kiln, pull the plates out secs before pulling the knife out for quench. It is easy just keep an eye on you kiln a little better. The reason why aluminum works so well for this application is because it evenly dispercess the heat through out the plate. So having thicker plates or cooler plates gives the heat more room to travel or in your case having to work harder to to heat up.

I hope this helps.
 
bladsmth said:
I think a chilled quench plate would be only useful for those doing production runs, and needing the plates to stay cool, and not heat up as multiple blades are quenched.

In the average shop, it is probably unnecessary. Comparing a chilled quench plate to standard 2-3" thick aluminum plates is like comparing a 400 pound anvil to a 300 pound anvil. Is it better - sure! Is it going to make any difference to the average maker - Nope!
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Yeah, that's my take on it. For someone doing repeated quenches you'd want a cooled plate (or several sets of plates) but for most folks doing one or two blades at a time, you're going to be just fine with a nice heavy aluminum quench plate. You can freeze it for a faster quench.

An aspect that is of some importance, that is often overlooked, is the quality of the contact area. Makes sure your plate is properly flat for good contact, make sure you're pressing it flat to the work, and make sure there is nothing (such as a fold in the foil) keeping the plates from making good contact with the work.
 
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