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Sean McWilliams

Scientific Testing Proves the Value of Edge Packing

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Posted (edited)

Have you ever had doubts about the value edge packing. Just an old blacksmith's tale? What is it, does it work, how does it work? I set about researching this subject in 1988, publishing the results in Knives Illustrated Magazine in the 1989/Winter issue. The article, titled "Microphotographing Steel" featured 400X photographs of cross sections of forged blade steels. The photos reveal considerable grain refinement due to forging, but the proof of "edge packing" was inconclusive. And there remained questions. Particle Metallurgy (CPM) steels were new on the market, and the question raised was "Does forging refine the grain in finer grain CPM steels?"

I conducted a similar study recently and published the results, the microphotographs, edge holding tests, and toughness tests. With higher magnification, 500X, and higher resolution photography, the answer is undeniably YES! Even in fine grained Particle alloys. I didn't really see it in the packed edge until I enlarged the photograph full screen on a 21" screen. Wow! something definitely different happened at the edge. Carbide particles were not just randomly finer and finer, but arranged like tightly stacked stones of a defensive wall. To further prove what this does for a forged blade, I did edge holding tests on stock removal, just forged, and forged and packed samples. Forging improved edge holding by a factor of 2.63, over stock removal, and edge packing improved edge holding 1.37 X over the forged blade. Bending tests proved significant improvements in toughness. I published the full story on my web site https://seanmcwilliamsforge.com/scientific-knife-testing-proves-performance-and-durability-of-sean-mcwilliams-knives/ Photos attached here are not full size, so if you want to see them on a big screen, I can email them info@seanmcwilliamsforge.com

45degbend.jpg

Forgepacked.jpg

Edited by Sean McWilliams
Add link 2 people got 404 errors on my web site
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Forged means shaping, tapering, drawing and thinning the edge. Packing occurs at the last heat level before austenite formation, above the point where "work hardening" occurs. This temperature is different for different alloys. I pack my edge with a lighter hammer (1 1/2 lb.)  use 2 1/2 lb- to 5 lb. for forging. Light, quick blows along the edge turning side to side evenly. Gotta move right along before the blade is too cool. At that heat, carbide structures have formed, but not cemented, so I'm just jiggling the carbides into a tighter configuration. This is a final step, as further forging upsets the packing. It does make a difference- I can tell.

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Dont know why this was sent to me as a personal message... maybe its a bunch of mumbo jumbo and you didnt want anyone who knows about this stuff to see it. I really dont like being misinformed or treated like a fool.

"Steven,

Packing is a final hammering on the edge of the blade, light, quick blows, turning side to side, moving quickly. This needs to happen, of course, at a heat well below critical, and above too cold, so work hardening is not occurring. The heat colors vary for different alloys. I do this with a much lighter hammer than I use forging, idea is to tighten the carbide crystals at a heat above austenite/cementite/pearlite formation. I'm not shaping or thinning the edge at all. Like shaking a cereal box, it's still the same weight, but the spaces between the corn flakes are much smaller. If I return the blade to the fire for more forging the packing goes away. So the "just forged" blade didn't go through this final step."

So its done above and below critical, at the same time.

When you shake a box of cereal and it settles to the bottom there will be empty space in the top of the box, when you are done shaking the knife where is the empty space that results from the packing? You cant move the carbides without something else taking their place.

 

I suspect what is happening is one of two things

1. You have given your blade a few extra normalizations with below critical forging further refining the grain

2. Im dumb

 

I could be wrong and ill accept what you say if its true. If you can shake the blade in a way that moves carbides to the edge then maybe hitting the edge of the blade against your anvil at the packing temperature would be even better than tapping the bevels.

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Steven,

The answer would be None of the Above. I didn't know I was sending it as a personal message, I reposted as a comment, subsequently. I was using the corn flake analogy as an analogy to describe what packing does. There is no empty space. I am actually hammering the bevels near the edge of the knife and on the anvil. I'm not shaking the knife or tapping the bevels.

  • Temperatures above and below critical cannot exist simultaneously.
  • Normalization and forging are separate processes. Forging is forging, normalization is heating the steel to critical and letting it cool in still air.
  • Forging below critical does indeed refine the grain, heating much above critical does indeed cause grain growth.
  • My intent on posting this information is to inform and educate in pursuit of better blades.  So I can recommend some additional reading: TOOL STEELS for ENGINEERS; Pendelton, Luersson, and Palmer. The Mystery Within Steel; Leon Borgman Univ. of Wyoming. THE ART OF BLACKSMITHING; Alex Bealer.

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You know, I should have said "light hammering on the bevels along the edge of the blade..." Not "...hammering on the edge of the blade..." My Bad, sorry for any confusion.

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Thank you for the clarification about the personal message, that does change my mood about this whole thing. 

However, I understand everything else you have said and I still dont believe in edge packing as it has been brought up and dismissed several times here. Though, your explanation is a little different than the others ive seen.

 

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Sorry, Sean, when someone advertises themselves as being "foremost" in something I generally reach for my hip boots.  Funny how I've never heard of you before.  A really great man's reputation usually is advertised by other people.  Edge packing, also known as work hardening the edge, has been done.  With cupric alloys it is the only way to harden the edge but with steel as soon as you austenize the steel the crystalline structure of the iron matrix will reform and it will reform again as it returns to ferrite.  The best way to refine the grain is by heat cycling the steel and to refine carbides you want to heat to non-critical and allow to cool slowly in an oven or in insulating material.

Doug

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Im pretty sure the forged vs. Stock removal debate has been settled as well.

Unless you do stock removal from a steel casting (or a crucible steel puck I guess) all steel has already been forged at the foundry.

 

If you edge pack a blade with this method then you wont be able to heat the blade for hardening without undoing the edge packing.

 

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Joel, Thanks for the very scholarly dissertation regarding cold working steel. Useful and informative, to say the least.

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Apologies to the 2 people who got the dreaded 404 white page trying to find my article on my site. I tried the link just now and it works. For your convenience I'll add it here.https://seanmcwilliamsforge.com/scientific-knife-testing-proves-performance-and-durability-of-sean-mcwilliams-knives/

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Posted (edited)

So I have been waiting for someone to show up and weigh in, as I'm positive that I'm not qualified... 

What I think chromium is the key here (based on a hunch). I dont mess with chromium steels as I know it requires long soaks at high heats to get the carbides into solution. So if you forged these carbides like your ordinary carbon steel, it may very well cause some segregations or odd structures... it would seem to me, if you did a quench from full critical unsoaked you might be left with some artifact from this kind of treatment. 

However, a known law is that whatever is done prior to heat treatment makes no difference if done correctly. A forged blade should preform the same as a stock removal blade in the hands of a competent heat treater. So I am a bit skeptical, because in your report, you claim a forged blade outperformed a stock removal blade with the same heat treatment by a significant amount... this may be so, but I suspect you didn't give the stock removal blade the kind of love and care it would have required to compete with the forged blade...

Again, I know just enough to get by with the simplest of steels, and I may be very very wrong. Waiting to see more views and opinions. 

Edit: I see now that Doug weighed in. I grabbed my waders too buddy! 

Edited by Zeb Camper

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I think part of the problem here is a bit of a misunderstanding.  First of all, I think we all need to agree on what we mean/think when the term "edge packing" is used.  My understanding is that this has historically been used to describe "packing the atoms at the edge closer together", thus improving the quality of the edge.  This is complete nonsense, and as such "edge packing" is not really a thing.  As I understand what Sean is saying, his "edge packing" is not that at all.  Sean is in fact mechanically refining the microstructure.  The degree to which this is being done and the actual benefits of it are another matter, but I only want to make sure we're all talking apples to apples here.  It is important to note that mechanical grain refinement is a thing, and its effects carry on to affect grain refinement through heat treat.  Generally speaking, it is preferred by makers (here at least) to have consistent properties, so a triple normalization is used to ensure uniformity.  He is also work hardening, but that is completely irrelevant as the hardening cycle is over-riding that work hardening.  

As I understand his description of what he is doing (and Sean, please do correct me if I am not properly describing what you are doing/saying; I'm not trying to put words in your mouth at all), he is working the steel along the edge while the metal is a mixture of ferrite and carbides.  The ferrite is being squished out of the way between the carbides, thus there is a higher density of carbides along the edge.  He then proceeds directly to a hardening heat treat cycle, presumably with tempering to follow.  

To really see what is going on with the microstructure, it would be best to be at least 2000x magnification (I like to use a 100x objective with 20x eye-piece/camera lens, etched with nital).  

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That is exactly what I was going to say, thanks, Jerrod!  Well, except for the metallography, which I am not equipped to do. 

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Thanks Jerrod! And, my sincerest apologies Sean. I hope you'll understand my skepticism and forgive my ignorance. 

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Jerrod, Thanks for jumping into the fray. You're right, the ferrite is being displaced as the carbide crystals are being packed more tightly together. This happens just above a black heat, maybe 1000F, (for the alloys I forge) but above the dreaded "blue-black brittle" range. Since this is a high alloy stainless, work hardening would crack the steel in a few blows. Work hardening does go away with higher heat, but the packing remains and is still there after hardening and tempering. Packing happens on the level of carbide crystals, in this case, chromium carbides. So, we need to be talking carbides, not atoms. The atoms are tiny, tiny and locked into the molecular structure, then, many, many molecules together form the crystals.

Alan, if I can post a .jpg file as large as 860 KB I'll be glad to post all the photos full size, when viewed on a large screen  (mine is a 21") the edge packing is truly visible. Otherwise, for those interested, I can email the hi-res photos to your email.

Zeb and Doug,  Skepticism about  Packing has been around longer than all of us put together. First I read of Packing was in a 1895 book by John Deere Co. describing the sharpening of plow shares, and how much "wing bearing" to put on a walking plow so it doesn't fall over in the furrow. So in those horse drawn days, "..the Blacksmith who didn't pack the plowshare was a thief and a charlitan..." who cost his customer 20 more acres of plowed field.

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860K is fine.  I have a 27" monitor in my office, and look forward to seeing that.

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It's hard to say without a full breakdown of your methodology, but this looks a lot like confirmation bias to me. If you want to demonstrate that your results are a product of forging and edge packing as opposed to thermal history, you need to design your experiment properly. I'd say you need 5 blades. The first is the control, heated, quenched and tempered, from the (I assume) fine spherodized state the steel is provided in. Next two are stock removal, one with edge packing, one without. Last two forged, again 1 with packing and one without. The important part is that all the blades, apart from the control, need to go through ]exactly the same thermal history, which means that a.), all the blades need to be kept cool while grinding and b.) all the blades are heated to the same degree in the same order - every time a blade is heated for forging or packing, the other three blades have to be in the fire, and while you're hammering , the other three have to be cooling on the anvil or an equivalent thermal mass. You cannot claim that your results are not a product of the thermal history unless you remove that as a variable.

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It is very important to note what is actually being discussed here.  It is not the old "edge packing" idea that by hammering at low heat you somehow compress the crystal structure which, as we all know, is not possible outside of a nuclear fusion reaction.

What Sean is saying is that with certain high-alloy stainless steels (extremely important part there!) you can concentrate the carbides at the edge by low-temperature forging, because the carbides in these alloys (again, very important point!) are larger than the ferrite matrix and, when forged at a heat after which carbides have formed but while the ferrite is still plastic, you can squeeze the ferrite out of the interstitial spaces between carbides.  This would not work at all on any low-alloy steel, because the carbides are not significantly larger than the ferrite.  You would still get grain refinement via forging, at the risk of microcracking. 

This is where the confusion is still coming in, because that quote from John Deere is assuming the old theory and this new idea would not apply (no large carbides in 1060 plow steel).  The effect they were seeing then is either work-hardening or grain refinement via a combination of forging and thermal cycling, and as we know, the finer the grain the better the toughness and edge-holding ability of any steel.  So yes, any grain improvement one could do to a plow point after forging it out would result in a noticeable performance increase.  But it ain't edge packing. ;) 

Also remember Deere got famous for being the first smith to make steel plows. Marketing being what it is, the company couldn't resist comparing the new steel plows with the old iron plows with wooden moldboards.  Deere was used to making those, and how do you harden wrought iron?  Cold forging to work harden.  See where this is going?  

All that said, I'd like to see those pictures that prove you can concentrate the carbides.  In theory it works, but as with all theories, pics or it didn't happen.B)

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Alan, Without compression, the photos are actually 2 MB to 3.7 MB. Photo #2.jpg is the stock removal blade, Photo #3.jpg is the forged blade, Photo #4.jpg is the forged and packed blade. These are cross sections of the three blades sent to the lab, #3 is somewhat fuzzy due to the focus of the camera.

Photo#4.jpg

Photo#2 (1).jpg

Photo#3.jpg

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Now I just need Jerrod to tell me what I'm seeing...:lol:  I see you also did a differential temper.  That can do odd things in magnified cross-sectional views. And this is all S35VN, right?  

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These are all S35VN cut from the same bar, and were differentially tempered. There were three blades sent to the lab, where they prepped and mounted them for photography. I next made three blades for the edge holding and toughness tests. All blades were heat treated in identical ways and bent each to the breaking point. BTW great comment about the New Improved Plow steel.

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Alan,

The colors are due to the etch, don't think they have anything to do with the temper.

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29 minutes ago, Sean McWilliams said:

Alan,

The colors are due to the etch, don't think they have anything to do with the temper.

I meant temper can affect microstructures visible in the etch, like the various phases of martensite.  

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