Oversoaking D2

[PMQ]

I recently made some knives using D2. I found a nearby heat treating workshop, they usually work with SKD11( Japanese's D2) for dies. So I just ask them to heat treat my blades with the dies. The goods are that they charge me much less, and the industrial ovens can maintain temperature more precise and consistent. The bad is that the austenising process is 1886F/1030C, lasts 2 hours, and could not be stop. To my understand, austenising usually takes 15-20 minutes, over soaking the steel will initiate grain growth, making the steel brittle. I have used the knives myself and sharpen them myself, but they seems to be performing quite normal, nothing unusual, but granted, I only use them for knife-stuffs, like cutting, not hard core torture test.

So does soaking D2 at 1886F for 2 hours causes any harm? Thanks.

 

[Stacy E. Apelt - Bladesmith]

Without their full HT process data, it is hard to say, but a 2 hour soak at 1886°F won't likely ruin the blades. Some of that time may be in steps as the steel rises to 1886°. Industrial processes often have a slow heating up to the austenitization point and then a 30 to 45 minute soak at austenitization. This could easily take two hours total.
If there was severe grain growth, the edges would chip out badly.

Larrin will hopefully give his thoughts

 

[PMQ]

I not sure how long or how fast they step up. I though reason it took them 2 hours to austenise is because the dies or mechanical parts are large and complex, so it must take longer for the whole piece to be uniformly heat treated. While it only takes 10-15 minutes to heat a thin blade thoroughly.

One of my customer told me that the D2 performs on par with his VG10, which sounds about right. And told me that he's thinking about ordering a chopper in D2, I know that D2 is not ideal for chopper, but that's what he asked, so I just want to make sure that the chopper is tough enough.

Thanks.

 

[shqxk]

Without their full HT process data, it is hard to say, but a 2 hour soak at 1886°F won't likely ruin the blades. Some of that time may be in steps as the steel rises to 1886°. Industrial processes often have a slow heating up to the austenitization point and then a 30 to 45 minute soak at austenitization. This could easily take two hours total.
If there was severe grain growth, the edges would chip out badly.

Larrin will hopefully give his thoughts

Most commercial vacuum furnace do really soak for 1.5 to 2 hours at austenitizing temp. This is not included the pre-heating process which might took another 1 hour.

 

[Cliff Carter Knives]

You likely will just be guessing until you run one of your blades through some significant testing. At the end, sacrifice the blade or a similarly heat-treated coupon by snapping it and seeing what the grain looks like.

If you’re making a chopper, you definitely want to know what it could/should be able to handle before delivering it to a customer.

 

[PMQ]

So I took Cliff Carter Knives 's advice and did a test on one blade. The blade I'm breaking is a Japanese Gyuto, D2 steel, austenised at 1030C (1886F) for 2 hours, follow by 3 temper cycles, thickness is 2mm (0.08"). Since I don't have any fancy expensive camera setup, let's hope this is good enough to see:

As far as I can tell, the grain structure is relatively fine, there are some patterns and visible particles. But this grain structure should be good to go.

 

[PMQ]

On second thought, after checking some images of grain structure on other posts, this grain structure seems to be on the bad side, but D2 should have larger carbides than most steel.
Can anyone evaluate this for me, it would help greatly, thanks.

 

[Cliff Carter Knives]

I don’t use D2, but it doesn’t look too bad to me. On the bottom of the blade in the pics, is that shadow or a color difference in the steel?

Hopefully someone with more experience heating and using D2 can jump in.

 

[DeadboxHero]

I learned from Larrin ya have to break em AQ and at a cold temperature to see the fracture grain better.

 

[N.W. Gean]

I learned from Larrin ya have to break em AQ and at a cold temperature to see the fracture grain better.

I was thinking the same. Breaking after temper won't tell you much.

 

[daizee]

I don't do D2 either, but my armchair internet backseat knee-jerk reaction is that looks coarse to me. I wouldn't expect you to be able to see even D2's large carbides by eye. it does look like there may have been a crack there already too (the dark section of the exposed cross-section), or maybe you did something else to that test piece.

Good on ya to test it.
I'd be inclined to dissuade a customer from using D2 in a chopper regardless to avoid replacing a broken blade.

My other inclination would be to not use D2 in kitchen knives, or anything else that should have an edge angle below 20dps, as the large carbides will probably tear out when under-supported for their size and possibly precipitate further cracking. Might cut very aggresively in the meantime! But that's my intuition based on reading and sharpening stuff (and making plenty of not-D2 stuff) vs. tightly controlled testing. Great stuff for dies, which usually have much more obtuse corners/edges etc. and may need high wear resistance across surfaces as well.

ETA:
I keep a couple of Larrin's posts/graphs handy:

Call for Charpy toughness samples

I do have pics. Here are the coupons. Small one is 1V, 41 mag., large one is S7, 308 cal. Scott

www.bladeforums.com

and with 1084:

Call for Charpy toughness samples

We have now added 1084 steel to the chart, as well as a couple more tempering temperatures for L6:

www.bladeforums.com

 

[A.McPherson]

Id be inclined to call it course as well, just from there pics...

You really shouldn't be able to see the grain with your bare eyeball.

 

[PMQ]

On the bottom of the blade in the pics, is that shadow or a color difference in the steel?

it does look like there may have been a crack there already too

I haven't noticed it until you guys pointed that out. I'm guessing that's a crack too, because that part is not supposed to be exposed, maybe the some water got into the crack.

I learned from Larrin ya have to break em AQ and at a cold temperature to see the fracture grain better.

I didn't know that until now, I'm reading Larrin's book right now but haven't finished it yet. So 'quench, wait for it to get to room temp, break' right?

I'd be inclined to dissuade a customer from using D2 in a chopper regardless to avoid replacing a broken blade.

Yes, I suggested using O1 or 52100 for a chopper, and 440C for a kitchen blade. But D2 seems to be very popular and trendy lately so everyone wants one.

Thanks for all the replies. I really appreciate it.

 

[mooniesdl3]

The CPM version of D2 is certainly tougher than the cast version but I wouldn't consider it a good choice for a chopper either. 52100, 5160 and 8670 would certainly make very tough choppers.

 

[daizee]

Larrin did some test with SPF-27 (sprayform D2) and toughness was up there, but almost anything with smaller carbides would be a better chopper.

440C also has large carbides and doesn't get as hard as the alternatives. I'm not sure there's a compelling reason to pick 440C for knives anymore if faced with buying new stock (great for bearings!) since 154CM seems better in every way that matters to knife performance. Even 154CM's carbides are too large for a kitchen blade's acute edge angles, IMO (have tested!). CPM-154, on the other hand.... Nice. Or AEB-L for scary sharp/tough if you can abide the lower wear resistance.

(Or Magnacut if you can get it )

 

[PMQ]

Larrin did some test with SPF-27 (sprayform D2) and toughness was up there, but almost anything with smaller carbides would be a better chopper.

440C also has large carbides and doesn't get as hard as the alternatives. I'm not sure there's a compelling reason to pick 440C for knives anymore if faced with buying new stock (great for bearings!) since 154CM seems better in every way that matters to knife performance. Even 154CM's carbides are too large for a kitchen blade's acute edge angles, IMO (have tested!). CPM-154, on the other hand.... Nice. Or AEB-L for scary sharp/tough if you can abide the lower wear resistance.

(Or Magnacut if you can get it )

AEB-L would be my first choice to make ... literally anything. If I want a chopper, I could get it 59-60 HRC and get crazy toughness, even tougher than 3V, or I can get it up to 63-64 HRC and get really good edge retention, rivaling CPM154, D2, plus AEB-L is not too expensive, I heard that the grindability is good and sharpening is easy so I really want to get my hands on some.

But I don't live in the States, I live in Vietnam, it's easier and cheaper to get D2 and 440C here, believe it or not O1 is harder to find than D2, I'm looking to get some 52100 for choppers but they're only sold in the form on round stocks (I'm a stock remover). It'll be very expensive to buy steel in small quantities from Jantz of AKS and ship them here, and large quantities is not suitable for a part time knife maker like I am.

If I have all the money in the world, I would get something along the lines of 4V, CruWear, and yes, Magnacut. People would be like, "how did you buy Magnacut" and I'll be like "I bought Crucible"