D2 Heat treat question

A

Andre V

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Oct 6, 2005
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I am using a new steel similar to D2 - name Bohler K110.

My question :

After i have taken the knife out of the oven after high temp soaking, how long should i keep it in the SS foil envelop? Should i remove the piece straight away or let the blade cool in the foil?? My understanding at this point is that i should remove the blade from the foil straight away and let it air cool.

I did use the search but couldn't find an answer to this.
 
i plate quench all my air hardening steel
i take out of the foil after the quench so i dont have to fight with a 1800f blade
 
2 things I could never understand:

1 - why so many people used to warn me about the burst of flame during a oil quench. It's not that exciting. It's downright tame.

2 - what's the big deal about juggling a hot SS foil packet? Sure, it can make for a high-stress, exciting few seconds...but is it really that bad?


The above two common comments I had heard so much as a newbie maker I was almost paranoid to heat-treat things myself. I figured you had to be nuts to even try.

Now I'm thinking...multiple salt pots...I can do that. :thumbup:





The answer to your question has a few "angles" to it.


If you are plate-quenching, leave the foil on.
If you are air-cooling only, remove the foil.
If you are forced-air-cooling, you can leave the foil on...but will need more time cooling.

Fastest quench is plate quench, no foil, forced air.

But, as noted, it requires a creative touch, a good sense of timing, and a little chutzpah.
 
I love D2...

I don't think you'll get the best air quench through the foil. For that matter, I'm not sure that D2 performs best as a knife steel with an air quench. A more sudden quench will keep the carbide grains smaller, provide better corrosion resistance (more free chrome), and possibly make a finer grain martensite. Perhaps Mete can chime in here? I also believe a more rapidly quenched D2 is tougher, again due to reduced chromium carbide size. Mete?

If you take it out of the foil while hot, it can decarburize in the air very quickly, leaving a nasty surface finish and softer steel on the very outside.

Butch's technique is a pretty good bet. Tightly wrap in foil, heat at temp 1850 ish I believe (for quite a while, due to dissolving the big 'ol carbides, 45 min ain't a bad idea), quench in foil between plates.

I have used that technique with great results. I have also heated in argon (not foil) and quenched in oil with good results.

I don't think the secondary hardening hump of this steel is good for knives, so I'd recommend tempering 500-525, which is the highest impact strength, and is also a great hardness for D2, around 61-62.

The steel was originally designed to retain austenite after quench to prevent growth in tooling and dies. You don't care about that, and the retained austenite is not helping your blade performance, so I recommend dry ice as part of the quench to finish the conversion. Plates, remove foil, water, dry ice in acetone, triple temper. I get dry ice at the grocery store and bring it home in a beer cooler. It's pretty cheap.
 
Soak at 1815°F to 1900°F (I do it at 1870°) for 30 to 60 minutes-longer for lower temps. I have used plates for the last few years-no muss no fuss. I don't like to air quench, there is too much oxidation during cooling. I oil quenched for a few years before I started with the plates. I can't tell any difference in results between oil and plates, except the plates are easier.

I temper three times for two hours each starting at 400°F and ending up at 425° to 450°.

I no longer cryo treat for reasons I have gone into here in other threads.
 
Nathan, taking it out of the foil to air cool won't cause any significant decarb but will cause scale which will have to be cleaned up. Plate quench in foil is so convenient more and more makers are using it....The major carbides are uneffected by quench speed.Martensite grains may be a bit smaller but the major difference is just how exactly the martensite forms and the stresses within it.I'm not sure that there's any difference as far as corrosion resistance. [They call D2 'semi-stainless' steel but with normal care it won't rust anyway]...BTW, the Bohler website makes no mention of cryogenic cooling !Crucible mentions cryo as a option.
 
mete said:
Nathan, taking it out of the foil to air cool won't cause any significant decarb but will cause scale which will have to be cleaned up. Plate quench in foil is so convenient more and more makers are using it....The major carbides are uneffected by quench speed.Martensite grains may be a bit smaller but the major difference is just how exactly the martensite forms and the stresses within it.I'm not sure that there's any difference as far as corrosion resistance. [They call D2 'semi-stainless' steel but with normal care it won't rust anyway]...BTW, the Bohler website makes no mention of cryogenic cooling !Crucible mentions cryo as a option.
Click to expand...


Mete,

See, this is why it's good having a bona fide metallurgist around. I appreciate your reply.

D2 is the one steel whose heat treat I've taken time to study. It was not discussed specifically in the one class I had that included metallurgy in college that I can hardly even remember, so my "education" is largely internet based (not really the real thing is it?)

I based a lot of this "knowledge" upon John D. Verhoeven's "Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel"

One of the things I took away from this text, and I've found a blirp this morning to quote, is the temperatures used to harden and temper stainless and the rate of cooling during the quench effects the corrosion resistance due to where chromium goes. I felt this was applicable because D2 is not so different from stainless steels in these respects. Poor assumption?

John D. Verhoeven
"there are two reasons to cool these stainless steels by quenching rather than air cooling:

(1) to reduce the amount of retained austenite as illustrated here, and

(2) to reduce K1 carbide precipitation on cooling and improve corrosion resistance."



I have read a lot of what you have to say on this forum, so I know you really know your stuff. While it is likely you know better than John D. Verhoeven, it is more likely I simply misunderstood him.

I'm saying this because it is my belief a person should know what they are talking about before offering their advice to others. Apparently I gave poor advice, but I want it known I didn't just pull it out of ass.

Any other information you'd be willing to share about heat treat of D2 would be greatly appreciated by me. It seems I don't know what I thought I did.

Thanks,
Nathan
 
Between you not phrasing your question well and me responding in the middle of the night things got confused !! Verhoeven is an excellent source, well written [at least for us metallurgists] and well researched..... "carbide grains", I wasn't sure what you meant here. In knife steels in general when austenitizing we dissolve some of the carbides but not all .They are called carbides ,not carbide grains.To understand that we dissolve only some of the carbides ,study the difference between a steel made in normal version vs crucibles particle metallurgy. If all the carbides dissolved in HT there would be no difference.....So we have the original carbides , then we have the carbides forming on cooling and even more on tempering. If we can keep more of the chromium in the matrix we can get better corrosion resistance....I've not done a specific test with D2 to determine how much difference there is .Stainless steels and tempering temperature are more often mentioned in terms of corrosion resistance.Of course some say D2 is not even true stainless !! ...I always take good care of my tools so I've never had corrosion problems with my knives.I hope this clarifies things .
 
So here goes for the 1000th post.

Getting the orange hot 1900f knife out of the pouch isn't so hard after developing a technique.
I work mainly with 440C and use a Paragon oven for HT.

This is what I do. Safey goggles on and gloves on. In one fluid motion, open door, reach in with tongs or pliers, and pluck foil packet and close door. Snip open packet with sissors in one hand, and the other holding it with pliers. Hold knife upright and not flat while doing this to prevent warpage from gravity. Simply reach in with pliers and pull orange hot blade from package and let the foil pouch drop to the floor while proceding to quench.

Repeat until all pouches are removed from oven.

One knife per pouch, sometimes two, but this risks causing warpage. So if you put two in per pouch make sure they are of the same length.
 
I've read some conflicting information on tempering D2. I followed a posted recipe but now I question the order of my dry ice/acetone step. Here is what I did:

Blade wrapped in SS foil
Knife in oven and ramp up temp to 1875 F over 10 minutes
1875 F soak for 40 minutes
Remove and plate quench while in SS foil using compressed air on plates to speed quench
Once cool to the touch, remove SS foil and place in dry ice/acetone bath for 4 hours
Immediately temper at 450 F for two hours
Cool to room temp and repeat 450 F temper for two hours

I am shooting for RC 61.

Reviewing info in Crucible's site, it says to perform cryogenic treating after the first temper. UDDEHOLM's spec sheet says to perform cyogenic treating immediately after quench and before the first temper. Does it make a difference which order this is performed? Any expert advice would be greatly appreciated.
 
You should understand the term "snap temper" which is 300 F and reduces some of the original quenching stresses which some find safer than going directly into the cryo. Higher than 300 F and you will stabilize some of the retained austenite .With or without snap temper is your choice - experiment ....Compressed air shouldn't do much for you as long as you're using at least 3/4" Al plates...The rest is fine !
 
mete said:
You should understand the term "snap temper" which is 300 F and reduces some of the original quenching stresses which some find safer than going directly into the cryo. Higher than 300 F and you will stabilize some of the retained austenite .With or without snap temper is your choice - experiment ....Compressed air shouldn't do much for you as long as you're using at least 3/4" Al plates...The rest is fine !
Click to expand...

Thank you Mete. I just did a search on "snap temper" and found some very good threads that you and others have described. One question that I did not find the answer to in those threads is, do you perform the snap temper for the full two hour cycle? I saw one person say 15-20 minutes but none of the other posts referred to time. I'd love to hear a second opinion rather than rely on a single post thread. Thanks again! This really helps.
 
I've seen a chart that illustrated stabilized retained austenite and time spent before cryo that shows you don't want to fool around much getting the blade into cold.

Mete is the expert here, but since he hasn't chimed in yet, I'll point out two things:

Retained austenite begins stabilizing immediately. The amount of retained austenite you will be able to convert depends on how long you wait to put the blade into cryo.

Tool steel manufactures emphasize the importance of not fooling around getting their steels into temper because a lot of tool and die work involves shapes with drastic thin and thick sections, stress risers and asymmetrical shapes. It is not unheard of for a mold or die component to crack during heat treat. That is not the situation with most knives. Unless you have a pretty unusual blade design or performed an edge quench in water or something else drastic, I don't think there is much need to hurry that first temper. It ain't gonna crack (unless you drop it).

So. If you're gonna bother with cryo, I'd think it best to skip any temper but go straight to cryo. I also figure, if you do snap temper, I'd keep it brief.

Just my 2 cents.
 
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