edge stability vs edge retention : 52100 vs 1.2% forged carbon (Zubeng)

[Larrin]

Johnston has been looking for F2 and O7 bar stock for a long time. But it is the class rather than the exact steel which is of interest, a cold work steel which has a high hardness and a fine distribution of tungsten carbides to enhance wear resistance. Hitachi's Super Blue for example is that type of steel.

http://www.paragoncode.com/temp/YSS_HCC_spec.pdf

I've also been searching for F2 and O7, and for that general class of steels , it seems the best bet is to find an obscure European steel that is similar, but it's difficult. I know that none of the American companies make it regularly anymore, though Carpenter used to make F2, and Timken Latrobe used to make O7, and both are available if you want to order a lot of it, which I don't. I've been considering e-mailing Hitachi and seeing if I can get a steel in the blue series, but I don't know if they'll sell me any or not. I'm still debating between Blue 1B and Blue 2B. I like the lower carbon of Blue 2, but I'd almost rather have the higher tungsten of Blue 1 along with it.

 

[Cliff Stamp]

F2 and similar steels were basically replaced by HSS as it became cheaper to make, that is what Johnson found when he went looking for it. I don't see why though you would have a problem buying the White/Blue steels as they are used extensively in knife steels, including by custom knifemakers, just not in the US so at worse case senario just contact someone like Carter and ask him where he buys it or ask Landes about steels like 1.2562. I'd be really interested in a edge stability/retention comparison of White/Blue and see where the intersection point lies at various angles/finishes.

-Cliff

 

[Larrin]

F2 and similar steels were basically replaced by HSS as it became cheaper to make, that is what Johnson found when he went looking for it. I don't see why though you would have a problem buying the White/Blue steels as they are used extensively in knife steels, including by custom knifemakers, just not in the US so at worse case senario just contact someone like Carter and ask him where he buys it or ask Landes about steels like 1.2562. I'd be really interested in a edge stability/retention comparison of White/Blue and see where the intersection point lies at various angles/finishes.

-Cliff

I don't have a problem with buying the White/Blue steels, I wasn't thinking about Hitachi until today, and it was just coincidental that I read this thread. I just haven't e-mailed them yet. Carter gets it from Hitachi, and I believe that he only buys it when already laminated. I'd want to be able to get it in thin sizes that aren't laminated to be able to use it in damascus, as well as some thicker sizes for knives, I could laminate it myself, or just buy it laminated for knives. We actually have a piece or two of Blue Super laminated with 410 that we got from Murray, but being able to get a piece or two from Murray isn't very useful, I have to be able to get a sizeable amount of it to use in damascus and knife making. We'll see how the e-mail works out, If all else fails, I guess we could attempt to work out something with Murray, but then we couldn't use it in damascus unless he wanted to try and order material that isn't laminated in thin sizes, and it'd be an annoyance for him.

Edit: I e-mailed Hitachi.

 

[Cliff Stamp]

Carter gets it from Hitachi, and I believe that he only buys it when already laminated.

I'd expect that because of his Japanese background, since you cut with the edge the rest of the blade is basically filler in thier eyes. I am impressed that they actually keep the larger blades functional as they made huge bowies which are basically almost all annealed steel except for a thin core hardened strip. It takes a lot of skill to use a knife like that and not have it warp.

...but being able to get a piece or two from Murray isn't very useful

I wasn't thinking of that but just getting his contact information and dealing with Hitachi directly. You could always broach them to import the steel for resale in NA. Regardless of if that worked out or not it would put you in a stronger position with them initially.

-Cliff

 

[TAKULU]

Cliff, have you test or verified that the edge hardness of Zubeng utility hunter is really at 67 HRC ? We guys here sometimes double their advertisement.

 

[Cliff Stamp]

No, that would be useful information however, not just for this case but for the knives in general. It would remove a lot of the uncertaintly about behavior if the hardness was known exactly for the knives. This of course doesn't tell everything about the heat treatment but it would allow more definate conclusions.

-Cliff

 

[db]

You could always try the scratch test with a known hard blade, Like the 1095 or M2 knife you have. It wouldn't give a perfect hardness test but should let you know if it is hard or close to the others.
http://www.bladeforums.com/forums/showpost.php?p=4036675&postcount=38

 

[TAKULU]

Thanks for the information, db.
However, we have already done the scratch test before and that is why the advertisement of Zubeng was in question here. As I know, Zubeng test the edge hardness with Vickers Hardness and then transformed it to the Rockwell hardness via transforming chart. The HRv has a micro indentation while testing the hardness, and we highly suspect that those guys who did the test probably had the indentor spot on the Fe3C or some carbides and thus gained the high values. It's abnormal with average carbon steel that has so high hardness and keeps its toughness at the same time.

 

[Cliff Stamp]

You could always try the scratch test with a known hard blade ...

A scratch test measures resistance to wear not hardness, it is influenced significantly by alloy content. For example filing VG-10 is much harder than filing 1095 even when the 1095 is significantly harder. You also need to take into account surface differences, you can for example crush the scratches in a coarse finish with a much softer steel just like you can damage the tip on a harder steel if you tried to cut mild steel with it. You could also get a really misleading result if the contact point was the focus of a carbide aggregate which is why filing is much more accurate, but again, has to be done against a benchmark on a known HRC on the same alloy steel. The most accurate way to measure hardness is to deform the steel and measure the deformation, that is of course what a HRC test does, there are various ways to estimate this by hand but you have to take into account the variables and it would be difficult to do so to the extent you could separate most cutlery aside from gross differences which tend to be obvious in sharpening and use anyway.

Takulu, the low carbon steels all actually have a torsional impact toughness peak at the maximal hardness, they all actually get both weaker and more brittle when they are drawn to 58/60 HRC.

-Cliff

 

[db]

LOL Cliff then do nothing and continue to try and pass off your BS as a scientific test. Of witch you don’t even have any idea on the hardness of half of your samples. Funny since it seems hardness was one of the factors you wanted to test. By the way I didn’t say the scratch test was the best or even a real good way to test hardness, but it is better than nothing, and you can tell a difference of 67 rc from a 60 rc by doing it. I know this because I just did it with a all hard M2, hard 1095, and a ATS 59-60 blade. Other than not watching how the edges dulled, and not knowing the hardness of half of your samples, I think you have a great test that could be very informative. Keep up the good work.

 

[Cliff Stamp]

Of witch you don’t even have any idea on the hardness of half of your samples.

Not having any idea would mean you could not tell if they were annealed or full hard which is obviously false even without any careful examination. Measuring a small difference of 1-2 points would be difficult without equipment which is why such was designed. I can also obviously infer the hardness from comparison edge holding tests on similar blades such as was done with the multuple S30V/ZDP-189 blades or reference them against known benchmarks such as Johnstons, Wilson's, Kirk's, etc. . . Wilson did offer to hardness test any knives but the border makes this problematic because any folders can be seized at will and there are issues with fees even on knives shipped to and from friends. I'll likely have him tests these two though as I am curious enough about the performance that I'll pay the cost to get the information. You also have to damage the blades significantly to do the tests, you have to grind flats on the blade to get the test as it is very difficult to accurately test curved/angled surfaces, there are correction factors that can be applied for various geometries however the last time I talked with a technician about this they noted this was essentially something you would only do if you had to and to really try to avoid it. The best way it to grind a flat right into the edge and the spine and thus test right into the edge.

Funny since it seems hardness was one of the factors you wanted to test.

As I noted in the above, the main purpose of that comparison was to show the difference between edge stability and edge retention and how the exact same blades could therefore have very different cutting lifetimes even when the media cut was the same and the edge angle was the same depending on how the media was cut and the finish used. I was origonally going to use D2 and 52100 but used the Zubeng light utility as I need to benchmark it anyway.

Yes, various materials test would be use as these would allow the formation of a model which determines how these properties are reflected in the performance. However the actual performance of the knife is obviously of value independently. If a knifemaker describes the performance of a knife he has made it is obviously useful knowledge even if he doesn't know the hardness, carbide size, grain structure, etc. . Primarily of importance from a user point of view is of course the performance directly.

By the way I didn’t say the scratch test was the best or even a real good way to test hardness, but it is better than nothing, and you can tell a difference of 67 rc from a 60 rc by doing it.

A VG-10 blade from Spyderco (59 HRC) scratches Alvin's 1095 blade (66 HRC), the softer S30V blades I have (based on how they deform when cutting hard materials) easily scratch the VG-10 blade. Thus if you ranked hardness by that scratch tests you would have the blades in reverse order and be very misinformed. Based on HRC tests Wilson has done the softer S30V blades are likely 10 points softer than Johnston's 1095 blade however the very hard vanadium carbides will pretty much scratch anything, this is why those steels can still haev a very high wear resistance even when soft. It should be obvious scratch tests are problematic on non homogenous materials, for example both cardboard and carpet can scratch blades, even Wilson's and Johnston's which are hard/high carbide, but this doesn't mean cardboard/carpet is harder than the knives. You also have to be aware of scratches which just remove the surface oxidization and thus leave a bright line because that patina is really soft which is why carbon steels scratch fairly easy, as well easily scratched are rougher surfaces as they are weak and can be smashed down more readily. You also need to consider the difference in the contact geometries, a very fine point will much easier scratch a surface than a blunt one as the contact pressure is much higher.

As I noted you are basically checking wear resistance not measuring hardness, this is actually one of the ways wear resistance is measured using a diamond pin. The scratch test for moh hardness works because you are looking at a very coarse change and you don't have the effects you have in steels where you can have a mixture of moderate hardness steel matrix with intense hardness alloy carbides. If you wanted to check hardness then do a direct hardness test which means measure the resistance to deformation because that is what hardness actually measures. Take the edge of a file (or glass, or ceramic, something harder than the knife) and put it into the edge and then load the spine of the knife and measure the indentation. You would of course have to have the geometries very close and given how strength and stiffness are strongly above linear you would be only able to make a coarse estimate without basically reinventing a hardness testor.

As I noted you obviously can infer this from use watching how the edge deforms and the level of edge retention assuming you have used enough other knives. This is why it is immediately obvious that machetes or cheap stainless kitchen knives are fairly soft. You can also estimate it from the responce of sharpening. The guys who have had Wilson reharden blades for example will note it sharpens differently and this experience then allows them to judge the hardness of other steels. But again this a nontrivial process as you also have to take into account alloy composition and geometry.

-Cliff

 

[TAKULU]

Takulu, the low carbon steels all actually have a torsional impact toughness peak at the maximal hardness, they all actually get both weaker and more brittle when they are drawn to 58/60 HRC.

Cliff, this is an interesting information for me, thank you.
However, do you mean that of the low carbon steel or high carbon steel? Steel with 1.2wt% C is a high carbon steel.

A VG-10 blade from Spyderco (59 HRC) scratches Alvin's 1095 blade (66 HRC), the softer S30V blades I have (based on how they deform when cutting hard materials) easily scratch the VG-10 blade. Thus if you ranked hardness by that scratch tests you would have the blades in reverse order and be very misinformed. Based on HRC tests Wilson has done the softer S30V blades are likely 10 points softer than Johnston's 1095 blade however the very hard vanadium carbides will pretty much scratch anything, this is why those steels can still haev a very high wear resistance even when soft.

I found that this phenomenon is apparent in the scratch of talonite knife with other knives, too.

 

[db]

Yup, scratching for hardness is a feel thing that is why I said it isn't the best way to test for hardness. I do have both a Calypso and a hard Alvin knife to check. I also have an all hard M2 blade as well. To me the harder blades have a different feel. It does help to have a reference blade, and use more than 1 knife.

 

[Phil Wilson]

Cliff, I would be happy to hardness test any knives you or someone else wants send to me. I even have a 67 test block to use for reference. Just cover the shipping and insurance cost to and from. My PO box is on my web site and I can give you the physical address if you e mail me. If you can get a sample of the mystery steel in a flat piece that is the best situation. The option is a large enough flat spot on the blade. I broke a diamond penetrator messing around with taper edges and I would want to be careful not to do that again. PHIL

 

[Dog of War]

I was also surprised at how fast they both dropped in sharpness early ....

This fascinates me, Cliff. Before trying to be somewhat consistent and quantitative in looking at blade performance I often felt this was the case, and now accept it as fact. But I've begun to wonder if there isn't something going on here, at least in some instances, I can't recall reading or hearing about. So at risk of going OT ....

When sharpening some blades to a very high level of push cutting sharpness I've noticed not only that initial sharpness is lost quickly, but after a fairly small amount of work will actually be below where it would be if not initially taken to such a fine edge.

An example is a non-laminated carbon steel Eriksson Mora I've been using. The large primary bevel is about 10 degrees/side. Patiently adding a very light microbevel of 15 deg/side with fine ceramic, this knife can push cut newsprint about 2.85" from point of hold, and light stropping takes this to about 3.2".

Making fuzz sticks out of small ash branches about 3/8" diameter, total of 50 diagonal push cuts using a single section of the blade, sharpness of the stropped edge falls substantially behind the unstropped edge. The difference is quite gross, the originally stropped edge not even wanting to bite on a thumbnail and only marginally push cuts newsprint.

Puzzling over possible explanations I've thought that the stropping could be making the edge weak and irregular, but I'm not seeing this effect on most knives. This makes me wonder if it's possible that I'm working at or near the limit of edge stability for this blade - so where finishing only with fine ceramic the edge is reasonably stable, further refinement exceeds it.

Now here's the question that interests me: assuming this is the case, could it be that when the stropped, unstable edge fails, it causes steel behind it to pull out or weaken, causing sharpness to quickly fall below the unstropped state? By this I mean not due to any irregularity caused by stropping, but simply that so fine an edge is created it not only fails quickly but does added damage in the process?

I've run this knife through enough sharpning cycles and worked it carefully enough that I don't believe this is due to a residual wire edge. Also leading me to suspect this is right near the limit of edge stability, increasing the microbevel by about 2 deg/side eliminates any tendency to do this.

Wondering what others think....

 

[Cliff Stamp]

Cliff, this is an interesting information for me, thank you.
However, do you mean that of the low carbon steel or high carbon steel? Steel with 1.2wt% C is a high carbon steel.

I meant to type "low alloy carbon steel", meaning basically any steel without a lot of the temper resisting alloys like chromium. There is an embrittlement peak at around 500F for the low alloy carbon steels like 1095,O1, 52100, etc. . This is called temper embrittlement of 500F embrittlement, or one step embrittlement.

I found that this phenomenon is apparent in the scratch of talonite knife with other knives, too.

Yes that is a dramatic case because the knife is actually quite soft, ~45 HRC, but has a massively high carbide volume and they are huge, ~50 microns. You are testing grindability so it is influenced significantly by carbide type/volume. This has many times causes people to form misconceptions like stainless steel is much harder than carbon steel because in general all the modern cutlery stainless has a lower grindability than the traditional low alloy carbon cutlery steels.

If you can get a sample of the mystery steel in a flat piece that is the best situation.

Yes, unfortunately this is often not the case on knives, especially the ones which are differentially hardened and thus you have to grind opposing flat spots on the knife to mount it, you also have to finish grind the surface as you won't get a HRC reading on a rough surface. The shipping cost also isn't insubstantial because of border issues which can cause any folders to just be siezed and inspection fees and even full duty tax can charged to any knives. Plus as well I can rank the hardness by other use so it is basically a precision refinement. For example :

The two lower performing Spyderco S30V blades are significantly softer than the Military by use. The Manix in particular actually had the entire edge take a dent and be pushed to the side. Now if you look at the results of the fitting then the A value is Manix > Paramilitary > Military which supports that hardness ranking.

It would indeed be useful though to have them all HRC tested and if you lived within driving distance I'd likely be constantly hassling you to test them. But at shipping costs of about $25 a knife then I have to weigh that information which would be a slight refinement vs actually obtaining more knives, more material to cut, etc. .

Making fuzz sticks out of small ash branches about 3/8" diameter, total of 50 diagonal push cuts using a single section of the blade, sharpness of the stropped edge falls substantially behind the unstropped edge. The difference is quite gross, the originally stropped edge not even wanting to bite on a thumbnail and only marginally push cuts newsprint.

The stropping is done on the same 10/15 bevel after the ceramic finish? What is the compound?

This makes me wonder if it's possible that I'm working at or near the limit of edge stability for this blade - so where finishing only with fine ceramic the edge is reasonably stable, further refinement exceeds it.

The edge stability of the low alloy tool steels is very high, they are all class I (Landes) when properly hardened, however that knife isn't going to be of that level as it is under hardened, however it should still be very high compared to almost every modern knife steel.

By this I mean not due to any irregularity caused by stropping, but simply that so fine an edge is created it not only fails quickly but does added damage in the process?

Yes, if the edge fails prematurely due to not being stable enough the B coefficient can actually rise above 1 which means that the rate of blunting is actually proportional to the amount of blunting which is indicitative of heavy deformation/fracture. This is why burrs are a problem because they crack/tear off and can be smashed back into the edge or just fatigue it as they are bent repeatidly until they fail. Just bend a butter knife back and forth and see how much metal back from the point of failure is heavily damaged.

Also leading me to suspect this is right near the limit of edge stability, increasing the microbevel by about 2 deg/side eliminates any tendency to do this.

So it is 10/17?

-Cliff

 

[Larrin]

An update on purchasing Blue Super, I got an e-mail saying that the American representative for Hitachi Specialty steel is gone until the 23rd. I guess I'll have to wait. The German company Bestar e-mailed me and said that they don't have any O7 in Germany or the USA, and it has a very high minimum order.

I e-mailed Daido about their GM2 which is similar to O7: http://www.e-tokko.com/eng_vspe_1_2.htm, and I e-mailed Takefu Specialty Steel (VG-10 company) about V-Toku1: http://www.e-tokko.com/eng_vspe_1_2.htm

You'd think that with three different steel companies with tungsten carbon steels, one of them would be able to sell the steel to me, even if they are in Japan, so I'm hopeful, but I'll just wait and see.

 

[Dog of War]

The stropping is done on the same 10/15 bevel after the ceramic finish. What is the compound?

CrO, green stuff, 0.5 micron I believe. For Scandi grind knives I find laying the large primary bevel flat on the unfinished side of a soft leather strop with gentle pressure and stropping for a total of about 8-10" is very effective.

The edge stability of the low alloy tool steels is very high, they are all class I (Landes) when properly hardened, however that knife isn't going to be of that level as it is under hardened, however it should still be very high compared to almost every modern knife steel.

What I find most interesting is that a couple Eriksson 12C27M blades I have have no problem with the same 10/15 edge geometry. Frosts laminated blades with stated 61 HRC core also do fine like this, as would be expected; BK11 and Bark River I have with similar edge geometry also no problem. VG-10 (Spyderco) on the other hand I've always found needs a microbevel >15 degrees to hold a fine edge well, at least for this kind of work, and simple carbon steel blades hardened mid-50's I usually finish with a 20/side microbevel.

Yes, if the edge fails prematurely due to not being stable enough the B coefficient can actually rise above 1 which means that the rate of blunting is actually proportional to the amount of blunting which is indicitative of heavy deformation/fracture.

O.K. that's exactly what I was wondering. This would seem to have some interesting implications when comparing blades, I assume you could see some startling changes in relative performance of two blades as you adjust edge angles and finish.

So it is 10/17.

Right. Just a very minimum microbevel at 17/side and the problem doesn't seem evident at all.

Thanks for the reply, Cliff. Your extended cutting ability model now takes on more relevance for me, and is very helpful.

 

[Cliff Stamp]

VG-10 (Spyderco) on the other hand I've always found needs a microbevel >15 degrees to hold a fine edge well, at least for this kind of work, and simple carbon steel blades hardened mid-50's I usually finish with a 20/side microbevel.

This all makes sense given the expected properties of the steel. VG-10 is much more coarse than 12C27M and the softer carbon steels are much weaker and the edge needs to be more obtuse to give it the necessary strength. It is rather interesting to note that this was one of the myths that Swaim first exposed.

As with all myths there is usually some element of truth. When Swaim reground edges and lowered the edge angles he got much better cutting lifetimes for a number of reasons. This directly opposed common perspective at that time which is that if you went from 22 to 15 the knife might cut better initially but would soon drop behind the 22 degree blade, this really isn't true for most materials people cut.

You can refine this further by making the bevel more complex. Instead of simply going from 22 to 15, go to 15/20 and you get (for the most part) the cutting ability of the 15 and the strength of the 20. This of course is no different than the natural extension of just putting an edge on a bevel and not simply taking the primary grind right to the edge.

I assume you could see some startling changes in relative performance of two blades as you adjust edge angles and finish.

Indeed. What the above should make obvious isn't simply the performance of those two knives but a general point about how edge retention is very dependent on how materials are cut and for how much. You can easily have a case where blades are not significantly different or are radically different or the difference even inverts by simply changing the grit, the material, how you cut it, and of course the angle of the edge. This is why I would like to see more specific statements rather than "BT-3X has excellent edge retention." because that is like saying "The RangeFinder has good balance.". The statements are undefined.

What we need to see are more posts like yours, sodak, thom, gud4u, etc., where people get very specific about steels they have used and illustrate how to optomize them. You compile enough of this information and you will very quickly allow definate correlations to be made on steels. It would be nice to see a separate forum for this, maybe an email list or yahoo group. I think a general forum like this one is of course very useful, but I think there is also a place for a strict discussion on comparative work.

-Cliff

 

[db]

As with all myths there is usually some element of truth. When Swaim reground edges and lowered the edge angles he got much better cutting lifetimes for a number of reasons. This directly opposed common perspective
at that time which is that if you went from 22 to 15 the knife might cut better initially but would soon drop behind the 22 degree blade, this really isn't true for most materials people cut.

You keep saying that this was the common thought of the time. That just isn't true. At least not true for anyone who used and sharpened their own knives. There is even published writings and articals about this. Just to name two, John Juranitch and Leonard Lee.

You can refine this further by making the bevel more complex. Instead of simply going from 22 to 15, go to 15/20 and you get (for the most part) the cutting ability of the 15 and the strength of the 20. This of course is no different than the natural extension of just putting an edge on a bevel and not simply taking the primary grind right to the edge.

That is the same asJJ was saying way back in the 60's and 70's.

It would be nice to see a separate forum for this, maybe an email list or yahoo group. I think a general forum like this one is of course very useful, but I think there is also a place for a strict discussion on comparative work.

I think this forum is a great place for these type of posts. If your not happy with it you could start your own if you wanted. Even though I disagree with you most of the time, you have had some very good threads and posts here, except when you start name calling and accuseing other posters of ill intent.