New Spyderco Serrata in CAST 440c

I just received Spyderco’s January Bite (newsletter) announcing their new Serrata fixed blade. What really got me curious is the description of the steel used:

"The Serrata is unique because its blade is made of cast 440C steel. This process involves making a wax model of the blade and then encasing the wax in a mold. When the mold is heated, the wax melts and leaves a cavity in the mold shaped exactly like the wax blade. Molten steel is then poured into the mold to create a pre-shaped blade, which is then heat treated, ground, and polished.

Unlike traditional rolled steel, cast steel creates a dendritic (“fern-like”) crystalline structure. Pioneered by knifemaker David Boye in 1981, this process infuses microscopic crystals into the steel that create microserrations along the edge. These microserrations increase the blade’s “bite” into the material being cut and enable it to retain its sharpness significantly longer than traditional steels. The crystal structure of dendritic steel gives its surface a distinctive look that sometimes includes minor pits created during the casting process. It also makes it somewhat more susceptible to minor surface scratches. These characteristics are completely normal and are part of the character of this G-10."

[www.spyderco.com]

A few questions:

- The "dendritic crystaline structure" mentioned above... is it not present in PM steels? What is it exactly?
- The "microscopic crystals"... What are they? Carbides? How are they formed? Are they not resent in PM steels?
- It is mentioned that the microserrations enable the blade to "retain its sharpness significantly longer than traditional steels"... So, would this cast 440C outperform PM high carbide steels (ie. S30V, SGPS, ZDP-189, etc.)?
- If this way of making knives has these benefits, why not make more blades this way?

[www.cliffstamp.com]

_______________________________________________________________________________________________

Always in search of a good choppa'

This is getting high interest (for this forum) which three threads so far asking about it. However there is not that much discussion on the Spyderco forum which is curious. I wonder if it is just the 440C label throwing people who are used to the high vanadium and PM steel approach.

Boye I believe is the originator (or at least popularized) as-cast steels on the basis of the carbide networks : [boyeknives.com] .

Thank you C Amber. 2,000 cuts from cast 440c vs 80 from VG-10 is an extreme difference. I did not find the technical aspects of the crystals and microserrations though (my questions above). Hopefully someone will come in and explain (Cliff?).

Cliff, I just checked Boye knives and they only mention it is a cobalt alloy of several elements. However, it seems that the alloy is secret as they do not mention its make-up percentage wise.

If dendritic steels are super performers, why aren't more knives made this way? Is it because they would not be tough enough? Also, are the crystals in these type of steels carbides? Why do they perform so much better than carbides in regular steels?

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CliffStamp
This is getting high interest (for this forum) which three threads so far asking about it. However there is not that much discussion on the Spyderco forum which is curious. I wonder if it is just the 440C label throwing people who are used to the high vanadium and PM steel approach.

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Caraldc
2,000 cuts from cast 440c vs 80 from VG-10 is an extreme difference.

This is the reason I'm interested in this. It sounds too good to be true frankly.


Chumgeyser on Youtube
E-nep throwing Brotherhood. Charter Member

Of course it sounds too good to be true, and that is why I have sent a Spyderco Serrata to Cliff for some unbaised testing...
Due 6th Febuary according to the shipping company...

I made the knives, so my very rough and un-scientific testing might have been skewed by my methods to favour my knife... no one has accused me yet of that bias, so let us see what Cliff has to say?

I give David Boye full credit for thinking of the original process, and it was an article in Knives Illustrated that got me thinking...

I have had no input frorm Boye, as my emails to him were unanswered...I was merely stated that I was going to cast knives, and thanked him for the inspiration...I did then, and still now regard him as a visionary...

And yes, 440C has thrown a lot of folk, as they see it as an inferior steel...



Edited 1 time(s). Last edit at 01/31/2014 01:30PM by Stuart Ackerman.

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Stuart Ackerman
no one has accused me yet of that bias, so let us see what Cliff has to say?

I'm certainly not accusing you of bias. It wouldn't matter who offered this information however. 80 cuts vs. 2000... I want to see independent testing. I'm hopeful that your steel does perform this well.


Chumgeyser on Youtube
E-nep throwing Brotherhood. Charter Member

Stuart, I am pretty thrilled with this performance. If this was done with 440C, can it be done with some higher carbide Steel? Why or why not?

Also, would you say this production method produces a blade that is less tough? Otherwise, I keep asking myself, why not make more blades this way? This method seems to greatly supersede the advantages that high carbide PM steels have over simpler steels (the difference in performance you have reported is just astonishing). Perhaps dendretic Steel is suitable just for smaller blades?

Chum, no worries...
I was not saying that you were mentioning bias of any sort...
I am surprised that no one to my knowledge has mentioned the idea...

When I did the test, i used a first batch knife, and bent the handle a tad before HT to make sure that I never sold the knife...
I never put a handle on it either, as I suspected that some folk in the future might want a one piece knife that they could cord wrap or scale themselves...I have since sent it to my biggest Serrata cutomer as a thank you...he has 6 ( I think?)

I used old poly prop rope from work, dirty and oily in places...some Spectra rope that was used for electrical transformer lifting, and a lot of linesman safety belts and harness, all passed their expiry date, so expect a bit of wear and UV damage there that might have baised the results?

I did the VG10 first, and the knife was scaled in carbon fibre, so was comfortable to use, much more than the Serrata...

The Serrata was then used with a 30 minute break in between cutting, to rest my right arm and shoulders,,,
I must have tired enough to mean that the overall cust could be reduced in numbwr, but it would still be high...
I had a bathroon scale that i wanted to use, but the top was glass, and my wife ( as they do ) said, "NO!"

I await Cliff's input...



Edited 1 time(s). Last edit at 01/31/2014 02:07PM by Stuart Ackerman.

Here is the original thread in british blades...
[www.britishblades.com]

You will notice that there was a 18 to 1 ration, and the VG10 in 3mm Thick did 95 cuts, so that makes it around 1700 cuts with the first Serrata, the one mentioned in the posts above?

I literally wore a Boye dendritic 440C blade out in about 5 years. While it was a good knife, and I'd not hesitate to get another if they were still available, I certainly don't recall anything like this level of edge holding over any other knife I had, which was primarily a Buck Scoutlite in 425M, a Benchmade 710 in ATS-34, and a Kershaw Random Task in 440V/S60V. I had a 440C paring knife, but it's use was not nearly as extensive. Boye's advantage over my other knives was it's very thin edge. I also used much higher edge angles than I do now, on all of the knives; somewhere between 20 and 25 dps, honed on a soft then hard Arkansas stone, followed by a Crock stick.

As-cast, hypereutectoid, stainless steel has a host of issues that would cause it to fall out of the top choice for knife blades, keeping in mind my preferences and testing methods (high polish, high sharpness edge holding, push cutting, etc.). Verhoeven's paper on wootz steel has a good intro to dendritic structures and why they form, though it is geared toward > 1% plain high carbon steel with trace (0.05% or so) amounts of vanadium. I have an entire book here somewhere on solidification and phase changes and you guys are going to force me to read it again, aren't you?

As an intro, liquid metal in a mold will solidify from the mold walls towards the center. For various reasons, like temperature gradients, differences in solubility of alloying elements, variations in melting points due to compositions, and many others, the solidifying metal forms the dendritic structure. The melt carbides Cliff speaks of will be in the little spaces between the intersecting branches of the dendrites, and thus will be arranged in the direction the metal solidified, i.e. from the mold walls towards the center. The spacing between the carbides will vary with the interdendritic spacing, which depends on cooling rate, alloying present, mold type, part cross section, and some others I'm forgetting.

The areas around the carbides will be relatively rich in alloying elements, while areas in the center of the dendrite braches will be relatively lean. This will lead to varying heat treating response, uneven carbide distribution, relatively large carbides in rows following the direction of the solidifying dendrites, and carbide devoid areas in between. Now, for the kind of self sharpening type of rough edge that lends itself to cutting rope and such fibrous material, this structure is pretty darn good. It's similar to the self sharpening effect Cliff noted in ingot D2 years ago.

However, this type of segregation and varying structure is the reason for things like hot rolling, soaking, vacuum arc melting, vacuum arc remelting, induction zone re/melting, and CPM technology. This structure also leads to much reduced impact toughness, strength, and ductility. However, for low stress cutting on fibrous and/or dirty material, it might work pretty darn good. There's no such thing as a bad microstructure, just a bad choice for application. The investment cast, 440C, Firestone Belt Axe has been a triple face palm mystery to me for years. I had to borrow my kids hand to get enough face palming to cover it.



Edited 1 time(s). Last edit at 01/31/2014 07:29PM by me2.

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Stuart Ackerman
Here is the original thread in british blades...
[www.britishblades.com]

You will notice that there was a 18 to 1 ration, and the VG10 in 3mm Thick did 95 cuts, so that makes it around 1700 cuts with the first Serrata, the one mentioned in the posts above?

That "normal" stock removed knife in the thread in BB was NOT 440C, but VG10...by the time that I had realised my mistake, i could not edit the post in BB...no matter...

BTW...The testing was done with other steels as different benchmarks, assorted ground factory knives that I owned at the time, but I just used the one that you see, for clarity...

me2...I would never accept batonning of Serratas for the reasons that you ended your post with...

I have used the phrase "self sharpening" in connection with my Serratas, but it was assumption, not scientific proof...

I am busy testing Kyley's "mystery steel" knife at the moment, and when I am done, I will do a Spyderco Serrata cutting test on poly prop rope and nylon and polyester strapping, and see how long it takes for the edge to stop shaving hair off my arms..

BTW, test shaving: means for me running the edge down my arm and seeing hairs pop off, not cleanly perhaps, but popping off none the less...

I will see if I can pick up an old Yellow Pages phonebook at work, and use THAT as the test cutting between rope etc



Edited 1 time(s). Last edit at 01/31/2014 07:48PM by Stuart Ackerman.

Your shaving test is much higher than the phone book paper. Knives I consider dull will still smoothly slice phone book paper.

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me2
Your shaving test is much higher than the phone book paper. Knives I consider dull will still smoothly slice phone book paper.

Fair enough...I will stick to hair...as long as I have some left...

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me2
The investment cast, 440C, Firestone Belt Axe has been a triple face palm mystery to me for years. I had to borrow my kids hand to get enough face palming to cover it.

In that case I guess investment casting is mostly done to get a convoluted shape for that would normally require forging, for cheap.

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Me2
The investment cast, 440C, Firestone Belt Axe has been a triple face palm mystery to me for years. I had to borrow my kids hand to get enough face palming to cover it.

I LOL'd.

_______________________________________________________________________________________________

Always in search of a good choppa'

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Stuart Ackerman

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me2
Your shaving test is much higher than the phone book paper. Knives I consider dull will still smoothly slice phone book paper.

Fair enough...I will stick to hair...as long as I have some left...

There in lies the problem with that test, among others.

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me2

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Stuart Ackerman

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me2
Your shaving test is much higher than the phone book paper. Knives I consider dull will still smoothly slice phone book paper.

Fair enough...I will stick to hair...as long as I have some left...

There in lies the problem with that test, among others.

The biggest problem I find with that is my wife hates the stubble on my arm when I hold her.

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me2

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Stuart Ackerman

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me2
Your shaving test is much higher than the phone book paper. Knives I consider dull will still smoothly slice phone book paper.

Fair enough...I will stick to hair...as long as I have some left...

There in lies the problem with that test, among others.

me2 ....Could you please elaborate? Hair or paper or...?

I would appreciate a method that is fair, and accurate enough for repeatablilty...



Edited 1 time(s). Last edit at 02/01/2014 12:55PM by Stuart Ackerman.

Well, hair is highly variable from person to person. Your arm shaver and mine could be different. There was a report hears ago about some guy testing makers "arm shaving edges" and each would shave the makers arm, but only a few would shave the testers arm. IMS, this was at a pretty large show. If you want consistency, use paper, but nearly every time I try it, when a knife will no longer easily shave, it will still slice phone book paper.

From what I have been reading on this thread I am leaning towards infering that cast 440C is good only for slicing cuts on abrasive media. But, no push cuts on hardwood, no batoning and certainly not chopping. Perhaps this explains why this material is not used widely in fine cutlery.

Might I suggest an experiment to see if my notions hold true? Would anyone be willing to put a chisel ground, back lapped, zero edge on one of the cast 440C blades and compare that to one with a double bevel? A differnce between the outer area and the center might be noticable, based on my half cocked theories above.

How much grinding is done after casting, how close is the as-cast edge thickness from the final thickness?

Cliff...
There is a 3mm lip on the edge to ensure steel fills up there, and that I grind flat, and the overall knife is ground flat and true...

I remove less than 0,3 mm overall, except for the edge apart, as noted above...

Here is a pic with as-cast blades and a finished one...



The Spyderco version is noticably thicker...



Edited 2 time(s). Last edit at 02/04/2014 11:31AM by Stuart Ackerman.

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CliffStamp
How much grinding is done after casting, how close is the as-cast edge thickness from the final thickness?

Re-reading the question...The edge is around 3mm thick as cast, and the final edge before sharpening should be less than 0.4mm...
All over is finished to 400 grit...Heat treatment is then done, and then 400 grit finish again to clean up...



Edited 1 time(s). Last edit at 02/04/2014 01:16PM by Stuart Ackerman.

Shot Show 2014 presented by Mike Janich...Serrata and Karahawk...

Chris, when I zero the blade I can do it on one side first and then gradually reverse it with subsequent sharpening.

Interesting. I was just curious to see if a user could notice the segregation in use. It may not be as severe as I'm used to thinking of, since the cross section is so small. When using the Boye blade I didn't know enough to look for any of this stuff, and kept an edge on it with the rough side of a cheap stone most of the time. Likely coarse enough that the touted advantages of the carbide structure were overshadowed.