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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making. |
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#1
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D2 Newbie!
I?m going to use D2 for the first time. I?ve read up on the HT process for this steel. I do have a few questions for those who have experience with this material. I searched the forum for D2 but didn?t find anything.
First, does it make a good spring or should I use it for the blade only, using another steel for the back spring? Second, I?ve read that it does benefit from a sub-zero treatment but I have read conflicting information about when it should be done. Is it best if done after hardening but before tempering, in between two tempering cycles, or is it done after tempering? Lastly, is it best to air quench or plate quench? I?m thinking it?s OK for the spring, plate quench, cryo. between two tempering cycles. Is there a better way? Any advice is greatly appreciated! Don |
#2
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Those are very good questions. I was wondering about it as well. I made a few fixed blades from D2 and I'm very fond of it. I also think that it should be good for a spring but never tried it.
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#3
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Quote:
I would think D2 would make a spring if heat treated correctly and drawn back to a range of 45-50Rc. Yes, the blade and spring will benefit from cryo. It's safer to cryo after the quench and the flash temper, between the first temper and the second. It doesn't matter whether you quench in air or between plates. The plates quench faster and will hold the blade straight if your flats are long enough. A final temper must be done after cryo. Every time. Heat treating air hardening steels is a very critical process and must be done correctly. It requires an accurate furnace and protected atmosphere or foil package. |
#4
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D2 is notorious for not having a great looking finish. You should know that in advance before you become frustrated.
__________________ God bless Texas! Now let's secede!! |
#5
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I will have to agree with Don Robinson, and Texas Jack as well. If you try to do a high polish on D2 is all but impossible, as it will look like orange peel on the surface, (the only way to do it is to use micron belts and it will take a lot of them; just like with S30V you'll probably spend 8 to 10 hours and probably 12 to 15 or more to do it).The best way to finish it would be a machine finish of about 600 to 800 grit. I have done one custom order folder out of D2 but it has been a long time ago. Contact Crucible steel and talk to one of the metalurgist about the spring temper processing temperature. Steve at Crucible in Arlington, Texas is the person I would contact. I really don't like making folders out of it mainly because I feel thet as tool steels folders I personally prefer to use S30V.
If you are looking for strength and toughness in a folder I really prefer using 440C, ATS-34, or CPM154cm; If heat treated and sub-zero quenched with at least one tempering after hardening, then sub-zero quench and at least one more tempering. This process will add strength, toughness, and durability to the above mentioned steels as well as the following ones. Even 440C will cut like ATS-134, or 154cm when a total heat treat process is done. I have been using sub-zero quenching in all of my blades/springs for the last nine years. I also do a triple temper on all of my blades/springs mainly because the initial one after the sub-zero quench is mainly for doing stress relief of the steel. You actually are doing two different stress reliefs the first one being after hardening the steel and the second one after the sub-zero quench. This was suggested to me by more than one metalurgists that I have spoken with over the years, this was also suggested to me by one of the great knife heat treater Paul B.. When I was doing contract work for one of the comercial people in the business Ispent a lot of time takling to a lot of people about the heat treat process. Just my two cents worth. Curtis Wilson __________________ Curtis Wilson Wilson's Custom Knives, Engraving, and Scrimshaw Last edited by CWKnifeman; 06-26-2009 at 01:51 AM. |
#6
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Thank you CW. So you are recommneding two sub-zero quenches? I understand 2 temperings but I'm not clear if you're sayin one or two sub-zeros.
I would not choose D2, but since posting my pictures around the various forums, a number of people have contacted me and asked for knives. Many of them wanted D2 and I went (Forrest Gump impression) "Okay..." DOn |
#7
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Don, your customers evidently aren't very familiar with the modern knife steels. D2 is a tool steel, used in tools and stamping dies. Long ago it was favored for straight knives simply because it was the best available steel that had enough chromium content to be just below "stainless steel". It was the most resistant to rusting until the mills came out with the first improved stainless knife steels, such as 440C.
Since that time, there are several knife steels that meet or surpass D2. !54CM, CPM154, S30V, for instance. Any of these steels will be better suitable for a folder spring. I suggest you see if your customers can afford an increase in price and go up to one of these steels. No one is exactly sure how cryogenic treating works. The mills and metallurgists have been working on this for years. It DOES work, though, and can be proven by the rise in hardness and embrittlement after cryo. And no, a few hours in your freezer won't work. One consensus is that repeated cycles of heat to cold, heat to cold, etc. is what makes it work. I'm quite satisfied, as are most makers, that one cryo below -100 followed by a 2 hr. tempering cycle is enough. As I said before, flash temper while your furnace cools down, then temper 2 hrs., then cryo for several hrs., usually overnight, followed by at least one more temper for 2 hrs. Last edited by Don Robinson; 06-26-2009 at 12:26 PM. |
#8
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I noticed an old friend has posted here. Pardon my interruption, please.
How in the world have you been, Andries Olivier?? |
#9
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I've been away from this forum for so long I should have re-introduced myself. Some of the guys who started out as newby's has turned professional since then. I kinda lost my mind way back and turned into a real bad dude. I even stopped making knives. Went to see a shrink and got diagnosed with PTSD. After a lot of councilling, medication and 4 months stress leave I think I'm back on track again. I recently started making tobacco pipes and upgraded my workshop for a fresh assault on knifemaking. I really want to take on auto's as it seems like a great challenge. Glad to see you are still around and and still going strongly. |
#10
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Newbie Don, this is the way I do my heat treat:
1. Hardening cycle 2. First tempering (stress relief) 3. Zub-zero (I use Dry Ice in 93% rubbing alcohol for at least six (6) hours). 4. Second tempering (stress relief) 5. Full tempering. Some might say that you do not need to do the last tempering. But, after many discussions with a lot of different people, I just feel that I am making the best knife out of the steel being used. Just one more note and that this I even sub-zero my Damascus just to make sure that all of the austinite convert to marstinite that will. Ohters may do it differently this is just my way. Thanks, Curtis Wilson __________________ Curtis Wilson Wilson's Custom Knives, Engraving, and Scrimshaw |
#11
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Welcome back, Andries.
I'm glad you were way down there in South Africa when you turned into a mean cop! To everyone: I should have added that I do a Rockwell hardness test every time I temper. I've found that after cryo the hardness increases again, depending on the type of steel I'm using. This temper/test/temper cycle usually forces me to temper one time before cryo, then 2 or even 3 more times after cryo with Rc tests in between to reduce the final working hardness to the point I want for each blade. When using cryo treatments I strongly suggest that a hardness test be performed at the very least after the final temper. If not, there is a risk of having a blade that's harder than you intend. |
#12
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Liquid nitrogen gives you about -300 F, dry ice about -100 F.At this point in time the only fact we know about cryo is that it reduces retained austenite. If you want to temper before cryo make it 300 F as higher temperatures stabilize some of the austenite. Always temper after cryo !!! A double temper , 2+2 hours should be used for D-2.A stress relieve temper after cryo does nothing for you.
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#13
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Quote:
Would you clarify this statement? Do you mean a stress relief at a lower temperature? |
#14
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Don, CW used the term 'stress relief ' and I shouldn't have repeated it.The first temper would be called a 'snap temper' and should be 300 F . It's used for a bit of safety factor before cryo. After cryo you have untempered martensite which should be tempered immediately. Thus it's just a temper and not for stress relief. If you want to be picky the normal tempering does in fact relieve some stresses though we don't refer to it as such.
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#15
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[QUOTE=mete]Don, CW used the term 'stress relief ' and I shouldn't have repeated it.The first temper would be called a 'snap temper' and should be 300 F . It's used for a bit of safety factor before cryo. After cryo you have untempered martensite which should be tempered immediately.
OK, that's what I usually do. It's scary to me to place a fully hardened piece of steel in cryo. |
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blade, knife, knives |
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