Weird D2 plate quenched blade

S

Steve Hayden

Joined
Mar 7, 2003
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4,270
Most plate quenched blades are a uniform dark gray shade. This one came out with what looks like a rainbow hamon. It was one of three that were all treated the same and was the second of three to hit the plates.

The colors are dulled in the photo and range from greens-yellow-reddish in distinct bands. I haven't tested the hardness yet, just got it tempered yesterday. I can't test the colored part anyway.

Any comments or ?
 
Were you blowing air between the plates onto the edge?
Not saying that would do it, as i've never done a plate quench...just wondering.
 
No air. D2 doesn't require any extraordinary fast quench, I like to get it done fast to control decarb and possibly, carbide growth. This was one of three and the other two came out the normal gray color.

The bands of color run all the way around the point and there is no decarb or black oxidation or pitting. I just posted it out of curiosity.

I will test the blade edge with a file and may just keep the knife for myself if I have any question or doubt about its quality. I was going to fill an order, but I don't like to take any risks with custom orders.
 
Maybe Roger will pop in, I don't know. May have been over heated? I've gotten a few back from heat treaters that looked kinda like that and they all performed like they were suposed to. Just sharpen and test and see what it has to tell you.
 
Was the blade in a foil wrap in the oven? The dull gray is the begining of decarbaration. Carbon Loss. You want to learn what a given type of steel likes as to length on time in the oven. Although the books state for instance Soak for one hour. at temp. They are referring per, inch of thickness. Far too Long on a finely ground blade which is usually only a few thousands in cross section at the edge. A lot of times the wild colors are from migration of elements in the foil wrap being used. Titaniun and Inconel can give some beautful colors. I use to get pre made foil envelopes years ago that were very consistant in knock-out colors. The colors were color fast and sold like hot-cakes. Thanks for reading M.Lovett
 
This blade was one of three that were all treated together, so I doubt that it was overheated. The othere came out gray like the tang on this one. That is the way blades always come out of foil wrap.

I am not really worried about it. The quench was fast, as plate quenches are and it seemed odd. The color are kind of neat looking, like a hamon in technicolor.

I have noticed that the edges often seem to start quenching while the top plate is still coming down in the blade. Right after laying the blade on the Al, the edge starts darkening. This is for fully ground blades.

mlovett, read the specs from all of the manufacturers of high alloy steels on minimum soak times. If you are soaking less than the minimum time, you are not getting the full benefit of the heat treatment. The time does not go proportionally to zero. For D2, no one reccommends less than 30 minutes minimum. Tool steels do not follow the same rules as simple Carbon steels in heat treatment.

The reason for this is the transition metal carbides-especially chromium need the time to dissolve. This does not start until ~1400°F, followed by Moly and others at ~1450° and finally Vanadium Carbides that don't dissolve until you get above 1900°F. The VC is very fine grained, sub-Micron down to about 20 nm and doesn't need the dissolution in D2. The super fine VC control the growth of the reforming carbides by pinning the grain boundaries, If these other grains haven't soaked long enough to fully dissolve, the vanadium can't do this and you are stuck at least partially, with the annealed carbide structure.
 
I often get wierd looking colors on high alloys after rapid air quenching. I have never plate quenched D2 but it is obvious the heat transfered through the spine area. The spine cooled first and enough to sink heat from the beveled areas. My guess is that is why the beveled area is colored as it is (not quenching quickly enough to avoid prolonged temperature transitions).

RL
 
I have had the rainbow effect on D2, ATS-34 and 440C. I have no idea what causes it, but I do use quench plates and compressed air. The latest D2 was perfectly flat because is was a special job for a friend, meaning it was not knife blades. One piece had the rainbow and one did not. The good news is that it has always been a surface phenomenon. A quick touch up on a belt and the color is gone. I figure it is some kind of surface oxidation, but cannot figure out why it only happens on occasion.
 
I dont know what might have caused this effect but the only possibility I can think of that: When it was cooling in the quench the foil broken somehow and let the air inside while the blade at about temper color temprature, the air oxidized the surface but as the thickness is varied at the edge the temprature of certain places at the edge was different so different colors. I assume the color at the very edge was bright (cold), and the color gets darker to the spine (hotter). The spine and the tang was so hot that they colored gray at the moment. This happened somewhat to a clay coated blade. While quench the clay has broke certain points and at the points where the clay was gone there was some rainbow effect...
Best wishes
Emre
 
Tai Goo (misternatural) did a lot of work on rainbow quenches that he documented on knifenetwork.com. There were some historical references that people dug up on them as well.
 
I followed the Tai Goo stuff on (then) CKD.

I thought this was neat on the high alloy.

Robert Hensarling emailed me an image of one he did that he couldn't get to load. I have attached it below. It was also plate quenched.
 
Thanks for posting the photo Steve. I don't know why it wouldn't let me load the thing. BTW, the steel here is D2 also. I lost the beautiful rainbow during the finishing process.
 
You are correct, I did and do read them often. they stipulate per inch of thickness. The hr. per thickness is because it take apx. one hr. per thickness to thuroughly soak to center. Not so when using only 15 tol 20 thousandts. Yes, I know that the transformations take a given amount of time, However the time isn't that long once at heat. We both need to understand both sides of the process. Both at heat as well as bringing to critical. Both take place in the oven, and are not totally exclusive, however are not the same action. One begins as the other has reach its zeneth. Thanks again > Lovett
 
I do not know what was ment by rainbows being ellusive. To me it is caused by dissimilar temperature transition.

RL
 
It was a joke. You know being light hearted ? Chasing rainbows, pot of gold, you know, fun. Lighten up. M. Lovett
 
http://www.bucorp.com/pdfs/UddeholmHeatTreatmentofToolSteel.pdf
http://www.bucorp.com/Products/ColdWorkSteels/DataSheets/aisi_d2.pdf

Uddeholm prescribes 30=60 minutes minimum depending on Austenitizing temperature, with additional time for thicker sections. For D2 they also reccommend slow heating to Austenitizing temperatures. They seem to have the most comprehensive heat treating instructions of all the manufacturers. Note from the first listed paper on general heat treatment of tool steels, they call for 30 minutes on all of them.

http://www.crucibleservice.com/cutlery.cfm#

Go to the D2 data sheet for Crucible, they call for 30-45 minutes without mention of minimum thickness. They do call for 1 hr per inch of thickness for tempers with a 2 hr minimum per temper.

http://ocw.mit.edu/NR/rdonlyres/Mat...4-4483-843E-A8B69AAC96E3/0/coars_kcr_2003.pdf

The above study looks at grain growth and effects of alloying elements in steels. There is a lot of good info in this, if you wade through (or around) the math.

Ferrite (BCC) to Austenite (FCC) to Martensite (BCT/BCC) is a set of diffusionless shear phenomena in the FeC system that moves through the steel at ~3000'/sec. The soak has to occur to allow dissolution/diffusion of the Carbon from Carbides to alloying elements in the FCC structure that can be trapped (quenched) in the sites that want to be the BCC sites , but are distorted into the Tetragonal sites by the differing size atoms.

In D2 we want to dissolve all but the Vanadium Carbides. These will be less than micron sized and will work to pin grain boundaries in the the CrCs and MoCs as they start to reform, aiding in keeping them small which will make the matrix stronger.

The VCs do not start to dissolve until the steel get >1900°F, so they are unaffected at D2 hardening temperatures. The rest start dissolving above 1400°F and require the soak time.

Another thing worth remembering is that the 1.5% Carbon in D2 is Wt%. Stoichiometrically, this will 5 or 6% carbon which will yield a significant volume of carbide content.

To compare soak times and grain growth between high alloys and Carbon steels is apples and oranges.
 
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