Thanks Ankerson for your reply. Agreed about not testing then
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Ranking of Steels in Categories based on Edge Retention cutting 5/8" rope
- Thread starter Ankerson
- Start date
Thanks Ankerson for your reply. Agreed about not testing then
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- 2,109
Thanks Jim, I wasn't sure whether it was "POWER" or "PARTICLE" metallurgy. It seems "PARTICLE" gets the nod here.
Chiral, M390 and Elmax can achieve 43J of toughness. The first in the low tempering range the second in secondary hardening range. High austenitizing, oil quenching.
Source:
"PMPLASTIC MOULD STEELS WEAR RESISTANT AND CORROSION RESISTANT MARTENSITIC CHROMIUM STEELS"
C. Kerschenbauer,M.O. Speidel
Institute of Metallurgy
ETH Zuerich
Switzerland
With that being said you mention "That said, we see stainless machetes all the time in which the steel is HT'd low to maintain free chromium and soft to improve toughness. At normal knife hardness (60+Rc) the edges will fracture readily under "heavy use" (impact)."
Rather the opposite it is true: HT 440C at 1000°C and then at 1100°C. I can prove it to you that the latter will be by far more stain resistant because more Cr will be left in solid solution. This is even more true for AISI 618 steels, like CM154, ATS34, CPM154, RWL34, CTS-BD4P. In this case austenitizing temps higher than roughly 1050°C will bring about the dissolution of M32C6 softer primary Cr carbides.
http://www.calphad.com/martensitic_stainless_steel_for_knives_part_1.html
http://www.calphad.com/martensitic_stainless_steel_for_knives_part_3.html
The fact is that knifemakers other than custom makers just want to mass produce, which means mass heat treat.
They mention superduper steel for the blade, then they underharden, which makes the blade softer, NOT tougher. The edge will turn and not break. But you'll be throwing away your money.
Every steel has its own use in cutlery. And has its own HT range which can favour edge holding a little bit, or toughness a little bit.
But let me say that selling folders in S35VN hardened below 60HRC has NOTHING to do with improving toughness. If you have to harden at 57-<59 either you've chosen the wrong steel or you're laughing at your own customers.
An Italian knifemaker (factory) sells a knife with Elmax blade @59HRC.
I could go on forever mentioning CTS-XHP @60.5HRC. Easily arguable that no deep freeze (so important in this steel) has been done.
No buddy, no excuse. We deserve what we pay for and Ankerson's work is so precious to this extent.
Differences in PM Generations have been hopefully addressed in another post of mine.
Hope this helps
Source:
"PMPLASTIC MOULD STEELS WEAR RESISTANT AND CORROSION RESISTANT MARTENSITIC CHROMIUM STEELS"
C. Kerschenbauer,M.O. Speidel
Institute of Metallurgy
ETH Zuerich
Switzerland
With that being said you mention "That said, we see stainless machetes all the time in which the steel is HT'd low to maintain free chromium and soft to improve toughness. At normal knife hardness (60+Rc) the edges will fracture readily under "heavy use" (impact)."
Rather the opposite it is true: HT 440C at 1000°C and then at 1100°C. I can prove it to you that the latter will be by far more stain resistant because more Cr will be left in solid solution. This is even more true for AISI 618 steels, like CM154, ATS34, CPM154, RWL34, CTS-BD4P. In this case austenitizing temps higher than roughly 1050°C will bring about the dissolution of M32C6 softer primary Cr carbides.
http://www.calphad.com/martensitic_stainless_steel_for_knives_part_1.html
http://www.calphad.com/martensitic_stainless_steel_for_knives_part_3.html
The fact is that knifemakers other than custom makers just want to mass produce, which means mass heat treat.
They mention superduper steel for the blade, then they underharden, which makes the blade softer, NOT tougher. The edge will turn and not break. But you'll be throwing away your money.
Every steel has its own use in cutlery. And has its own HT range which can favour edge holding a little bit, or toughness a little bit.
But let me say that selling folders in S35VN hardened below 60HRC has NOTHING to do with improving toughness. If you have to harden at 57-<59 either you've chosen the wrong steel or you're laughing at your own customers.
An Italian knifemaker (factory) sells a knife with Elmax blade @59HRC.
I could go on forever mentioning CTS-XHP @60.5HRC. Easily arguable that no deep freeze (so important in this steel) has been done.
No buddy, no excuse. We deserve what we pay for and Ankerson's work is so precious to this extent.
Differences in PM Generations have been hopefully addressed in another post of mine.
Hope this helps
chiral.grolim
Universal Kydex Sheath Extension
- Joined
- Dec 2, 2008
- Messages
- 6,422
Yes, i linked that paper in my post. But i have not found any M390 blades with that ideal HT, would be excellent indeed! There seems to remain an assumption that the longer/hotter you temper, the better toughness can be achieved, but this is not the case in ideal knife-hardness range. I would love to see 63Rc blades of M390 from major production companies. :thumbup: Instead, we get ~60Rc and nominal toughness below that of carbon steels like O1.
You are correct, I mis-typed: By "Ht'd low" I meant 'to low hardness'. Thank you for correcting that. :thumbup:
:thumbup::thumbup: Well said/typed.
Glad you appreciated
Thanks
Elmax, M390 and S90V have a distint peak in second. hardening range. As far as Elmax is concerned it will be also the toughness peak. For the other two SS it will not, but you'll be very close to it. No need to Deep-cryo in this case as high temp tempering will minimize retained austenite anyway. Just three tempers instead of the mandatory two.
No hope we'll ever find this HT in production blades, buddy. And very few custom makers are willing to do this as well. To my knowledge and purchase Elliot Williamson and Neels Roos.
Yet for sure an M390 blade could at least be brought to 62HRC via vacuum furnace, decent overpressure quenching (5bar) and deep cryo. It would make a world of difference against the usual 60.5HRC.
Thanks
Elmax, M390 and S90V have a distint peak in second. hardening range. As far as Elmax is concerned it will be also the toughness peak. For the other two SS it will not, but you'll be very close to it. No need to Deep-cryo in this case as high temp tempering will minimize retained austenite anyway. Just three tempers instead of the mandatory two.
No hope we'll ever find this HT in production blades, buddy. And very few custom makers are willing to do this as well. To my knowledge and purchase Elliot Williamson and Neels Roos.
Yet for sure an M390 blade could at least be brought to 62HRC via vacuum furnace, decent overpressure quenching (5bar) and deep cryo. It would make a world of difference against the usual 60.5HRC.
- Joined
- Sep 4, 2013
- Messages
- 440
But let me say that selling folders in S35VN hardened below 60HRC has NOTHING to do with improving toughness. If you have to harden at 57-<59 either you've chosen the wrong steel or you're laughing at your own customers.
An Italian knifemaker (factory) sells a knife with Elmax blade @59HRC.
I could go on forever mentioning CTS-XHP @60.5HRC. Easily arguable that no deep freeze (so important in this steel) has been done.
Couldn't agree more. I have many knives in s35vn and most are 58 to 60 hrc as usual. But I have 2 more, one at 60.8 and the other at 61.7 and you wanna talk about performance difference. At the same time the harder s35vn is just as tough and as easy to sharpen. I laugh at chris reeves bs excuse about why they run their s35 so low, im sorry but in a $450 id expect top notch heat treat. And dont get me started on hxp being ran at anything under 62 to 63. I love my millie and domino but im bummed cuz I know they could have been so much more. I know no production knife will have optimum heat treat and be at max hardness buf when you have a steel that can go to 65 hrc and that's what makes it great, why run it 4 to 5 points lower? We see how much better performance 1 to 2 points can do, so I think spydrco can easily run xhp at 62 and maybe 63 and still be in that safety zone that they like. I like xhp, obe of my favorite steels, I really would like to see it at 64, 65 hrc, it could maybe even give m390 a run for its money.
Differences in PM Generations have been hopefully addressed in another post of mine.
Hope this helps[/QUOTE]
An Italian knifemaker (factory) sells a knife with Elmax blade @59HRC.
I could go on forever mentioning CTS-XHP @60.5HRC. Easily arguable that no deep freeze (so important in this steel) has been done.
Couldn't agree more. I have many knives in s35vn and most are 58 to 60 hrc as usual. But I have 2 more, one at 60.8 and the other at 61.7 and you wanna talk about performance difference. At the same time the harder s35vn is just as tough and as easy to sharpen. I laugh at chris reeves bs excuse about why they run their s35 so low, im sorry but in a $450 id expect top notch heat treat. And dont get me started on hxp being ran at anything under 62 to 63. I love my millie and domino but im bummed cuz I know they could have been so much more. I know no production knife will have optimum heat treat and be at max hardness buf when you have a steel that can go to 65 hrc and that's what makes it great, why run it 4 to 5 points lower? We see how much better performance 1 to 2 points can do, so I think spydrco can easily run xhp at 62 and maybe 63 and still be in that safety zone that they like. I like xhp, obe of my favorite steels, I really would like to see it at 64, 65 hrc, it could maybe even give m390 a run for its money.
Differences in PM Generations have been hopefully addressed in another post of mine.
Hope this helps[/QUOTE]
I'm curious about the criticism of Chris Reeve's heat treat of S35VN, which seems to mirror the criticism of his heat treat of S30V. The hardness that Chris Reeve uses for S35VN is 58-59 HRc. Crucible recommends 58-61 HRc. Spyderco chose a hardness of 59 HRc on its mule. And other top makers use heat treats that produce similar hardness levels on that steel. For example, Spartan Blades runs its S35VN at 58-60 HRc.
I'll add that Shirogorov, which is highly regarded for its excellent heat treats of various steels, runs S35VN at 59-60 HRc.
I don't know how the peaks of toughness and strength vary with hardness, but it seems safe to assume that S35VN at 59 HRc will be tougher and easier to sharpen than it will be at 62 HRc. Wear resistance will probably drop. So it becomes a question of what you want.
Jim's tests and Hardheart's CATRA tests show that more acute edges can improve wear resistance when cutting rope, and Reeve tends to use pretty aggressive blade geometry on his pocket knives. My Sebenza in S30V at 58-59 HRc is 0.017 inches at the edge shoulders, which which front a thin, hollow ground blade. It tends to hold its edge well.
At the softer range, with good edge geometry to back it up, the Sebenza can cut extremely well, hold its edge well, be easy to resharpen, all while provided a tough edge resistant to chipping. The edge geometry and the steel carbides give a boost to wear resistance that make up for the softer heat treat.
I know there is a YouTube video out that found exceptionally poor results of a Reeve S35VN knife, but my understanding is that that test was flawed, although it has proven to have long legs on the internet. We've seen similar criticism of Elmax, which in my experience is an excellent steel.
The owner of Wicked Edge speculated that people have difficulty switching from the Sebenza's convex edge to a straight edge, basically leaving a wire edge that would give the appearance that the steel cannot hold an edge well.
Who knows what is really going on, but if there is solid evidence that S35VN at 59 HRc is some how a horrible choice, I'd like to see it. I haven't been able to find that evidence.
I'll add that Shirogorov, which is highly regarded for its excellent heat treats of various steels, runs S35VN at 59-60 HRc.
I don't know how the peaks of toughness and strength vary with hardness, but it seems safe to assume that S35VN at 59 HRc will be tougher and easier to sharpen than it will be at 62 HRc. Wear resistance will probably drop. So it becomes a question of what you want.
Jim's tests and Hardheart's CATRA tests show that more acute edges can improve wear resistance when cutting rope, and Reeve tends to use pretty aggressive blade geometry on his pocket knives. My Sebenza in S30V at 58-59 HRc is 0.017 inches at the edge shoulders, which which front a thin, hollow ground blade. It tends to hold its edge well.
At the softer range, with good edge geometry to back it up, the Sebenza can cut extremely well, hold its edge well, be easy to resharpen, all while provided a tough edge resistant to chipping. The edge geometry and the steel carbides give a boost to wear resistance that make up for the softer heat treat.
I know there is a YouTube video out that found exceptionally poor results of a Reeve S35VN knife, but my understanding is that that test was flawed, although it has proven to have long legs on the internet. We've seen similar criticism of Elmax, which in my experience is an excellent steel.
The owner of Wicked Edge speculated that people have difficulty switching from the Sebenza's convex edge to a straight edge, basically leaving a wire edge that would give the appearance that the steel cannot hold an edge well.
Who knows what is really going on, but if there is solid evidence that S35VN at 59 HRc is some how a horrible choice, I'd like to see it. I haven't been able to find that evidence.
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I don't believe that Bohler's 2nd gen = Carpenter's 2nd gen. My point is that although there have been several "generations" of PM technology, they all use their own proprietary production methods, variations on the "generations." They may be similar, but they are not exactly the same, thus they cannot be directly compared. I see over and over, repeated many times in a number of forums, where someone says that company X uses 2nd generation, while company Y uses third generation, implying that company Y's product is superior since it uses a newer, better production method. But this is simply not true, since the specific production methods yield very comparable results. Compare M390 and CTS-204P, for example. If you had two knives in these steels that were geometrically identical (same edge thickness, edge angle, primary grind angle, blade stock thickness), same edge finish and had the same heat treat, you would not be able to tell these two steels apart, despite one being so-called 2nd generation and the other 3rd.
The bottom line is that Bohler uses an improvement on their 2nd generation and calls it the 3rd generation. Carpenter uses an improvement on the "2nd generation" and calls it Micro Melt. Crucible uses ??? and calls it Crucible Particle Metallurgy. I assume it to be their own variation on the "2nd generation."
A post that N. Brian Huegel made on the Spyderco forum is useful (in M390 Mule thread June 2011 - note that Crucible is not discussed here, they use their own proprietary variation):
-------------------------------------------------------------------------------------------------------------------------------------------------------
"As part of my interest in understanding powder metallurgy, I sent an email to Ronald Long at Carpenter Technology Corporation. He is the Commercial Manager of the Knife Blade Products division. He has graciously allowed me to share it with the forum. Here is a portion of our correspondence.
Q: Per this Spyderco forum thread, in what began as a discussion about their latest Mule made with Böhler M390, I have attempted to compare / contrast with your CTS-204P. As part of the discussion, it has been brought up that your powder metallurgy is 2nd generation whereas Böhler’s is 3rd generation.
A: From one of Carpenter’s R & D managers: “The first generation powder product that was originally produced in Sweden by Erasteel and Anval (now CPP AB) consisted of air induction melting in a top pouring furnace followed by pouring the molten metal into a tundish from which the molten metal is bottom poured out of the tundish and is atomized to produce a coarse powder, typically -1000 microns or -500 microns.
The second generation powder product as practiced by Erasteel, CPP AB, and Böhler, consists of the first generation air induction melting process followed by pouring the molten metal into a heated, refining tundish called an “ESH” tundish (Electro-Slag Heated tundish), where the molten metal is heated with graphite electrodes (Erasteel and Böhler process) or a plasma torch (CPP AB). The refining tundish permits the molten metal to be purified (reduce the amount of inclusions). After refining, the molten metal is poured out of the bottom of the tundish and is atomized to produce a coarse powder, typically -1000 microns or -500 microns (the same powder size as the first generation process).
Böhler’s third generation powder product consists of the second generation process followed by a modified atomization process that produces a finer powder, typically 250 microns. Böhler claims the finer powder reduces the presence of coarse carbides compared to the first and second generation, coarser powder.
As noted above, CPP AB uses the second generation powder process. CPP BVL (BVL is our facility in the US and our source for CTS 204P) uses both air induction melting and vacuum induction melting coupled with the use of reticulated refractory filters in its tundish to produce 150 micron powder (finer than Böhler’s powder) for P/M tool steel millform products. CPP BVL’s powder manufacturing process does not directly compare to the European classification system of “first, second and third” generation powder processing. BVL’s vacuum induction melting + filtration process plus the use of -150 micron powder is cleaner than the third generation process. The air induction melting process + filtration process plus the use of -150 micron powder is equivalent to the second generation process with a finer powder than the second generation process.”
From Ron: As you can see it is not exactly an “apples to apples” comparison when one puts the processes side by side.
Effectively, from dimensional perspective, our “2nd generation” process produces a finer, 150 micron powder than their “3rd generation” process which is 250 microns. And I don’t believe they would argue that their 250 micron material would have finer carbides than our 150 micron material.
The other issue is product cleanliness. I have asked for information on product rejection rates for inclusions and have yet to find an example. I am not saying they do not happen; just that folks are having problems finding the last time it did happen. In my short tenure here I have not dealt with an inclusion. I will look to get you a better definition of cleanliness relative to our product.
Regards,
Ronald Long
Carpenter Technology Corporation
Commercial Manager- Knife Blade Products
His only concern in allowing me to quote him and Carpenter is that he does not want to get into a situation where he might sound like, or be accused of, being critical of Böhler-Uddeholm which was not his intent. I do not believe that this will be the perception and I sincerely appreciate his explanation and knowledge on the subject. I also invited him to participate directly with this forum and also encouraged him and Carpenter to consider establishing a forum or sub-forum of their own. Time will tell if this comes to fruition, however, I do believe that the above is a definitive expression of Carpenter Technology’s deep commitment to our industry and the future of cutlery steels.
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Also, From Sal (Dec 2012 in thread about Tenacious edge retention)
Jim,
I'm not all that convinced about "generation" differences. Other than "refinement". I couldn't get any explanation from the metallurgists involved as to actual physical differences that caused the "improvements" of each generation, nor a good explanation as to why it was better. Maybe it's just me? Or maybe it's a secret?
sal
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S35VN is a horrible choice against other SS, count Elmax, CTS-204P and M390 in. In toughness, in edge holding, in stain resistance, less finer grain, in PM technology.
Underhardening a dated and inferior steel does NOT improve toughness, let edge stability and edge holding alone.
Will eventually soften the blade, giving way to wire edge, that why Sebbies have convex edge and when you try to put a straight edge you score a wire edge.
IMHO the best knife in current CRK line is the Impofu http://www.chrisreeve.com/Impofu which has the proper steel and HT for the proper task.
I don't know in USA, but here in Italy a Large Sebbie with no bells and whistles costs 610EUR!!!! Per Ankerson's results S35VN at 59 has same edge holding of N690.....
Per Catra results S35VN needs an additional HRC point (62) to deliver as much as S30V at 61, so, sorry, this is the evidence you were looking for.
Beyond mere edge holding underhardening means that austenitizing temp is a lower than the one needed to achieve the optimal Primary carbides' dissolution (M23C6 mainly) thus bringing about less C free for hardness AND Cr in solid solution to stain resistance extents.
It all a matter of saving furnace and tooling costs.
Most of us are knowledgeable about sharpening an higly alloyed and high HRC blade. And able to choose among steels....the rest is bullshitting
Ankerson
Knife and Computer Geek
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- Nov 2, 2002
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- 21,094
S35VN is a good steel, it's just not taken to the higher HRC ranges in production blades usually for various reasons.
I wouldn't go that far, the manufacturers don't know who is buying their knives or what some ham fisted dude would be using them for so they compromise and produce knives for the general public.
Yeah most of the steels used could be taken a point or two harder in general, but we are back to the ham fisted dude and some others crying about how hard the knives are to sharpen.....
Remember we are a VERY SMALL percentage of the knife industry here, not the majority....
If all the knives were made how I would personally like them to be as in very thin and at high RC ranges for the steels it wouldn't be long before some moron makes a video trying to pound one of them through a cinder block or concrete or something else really stupid.... So that has to be taken into consideration also when talking about production knives.
While I would agree that knife knuts' purchases are a small percentage of knives bought by the general public, a knife that's over $400 or more is probably marketed to buyers who know a little bit more. IMO, there's no excuse for a knife that costs that much to exhibit poor cutting performance or poor edge retention.
I had a few expensive knives that didn't cut as well as some mass produced cheap ones, and I got rid of them quickly.
I had a few expensive knives that didn't cut as well as some mass produced cheap ones, and I got rid of them quickly.
Ankerson
Knife and Computer Geek
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- Nov 2, 2002
- Messages
- 21,094
Production knives are what they are as you know, price aside they are still production knives.
That's why we have Custom makers so we can get exactly what we want. :thumbup:
Notable exceptions lately that I have seen personally have been the BM 940-1 (S90V), BM 810-1401 (M390), and Spyderco LW Manix 2 in S110V so things might be changing some for the better...
Thanks for those thoughts and your expertise, Daberti. I've never used S35VN, so all I have to go on is the experience of others. I, too, would take Elmax and M390 or one of its variants over S35VN, but I have also seen a lot of excellent knife makers swearing by S35VN, even at sub-60 Rockwell hardness. It's difficult for me to believe that Chris Reeve, Sal Glesser, Shirogorov Knives, Spartan Knives and others are so far off on heat treat. Sal, in particular, has shown that he is more than willing to take hardness levels up pretty high and geometry down, especially for knives sold to the general public, so manufacturing costs of a higher heat treat are not the issue.
Chris Reeve's Impofu would be a beast at any reasonable heat treat. It's a giant slab of 3V steel well more than a quarter inch thick. He still runs it at what seems to be for him the sweet spot of hardness: 58-60 Rc. The mystery of that knife for me is what would it be used for. Chris seems to like large knives that are thick. His chef's knife in S35VN was dismissed by some expert reviewers, but not because of the steel or heat treat, but because the blade was too thick.
I watched the YouTube video on which the S35VN Sebenza failed after cutting rope. The whole edge bevel bent over, not just a wire edge. Who knows what that was about, but that experience is certainly not common. Chris Reeve puts a proprietary convex edge on the Sebanza, an edge geometry that he says took him 6 months to perfect. So someone comes along and converts it to a straight edge -- a conversion with well-known risks -- and who knows what happened. We never got a decent analysis of why that blade failed, just another internet legend of a supposedly bad steel.
Do you have any tests or links that you could share that show toughness of S35VN does not improve when the hardness is dropped from 62 Rc to 59 Rc?
There is a tendency for people to look for either the toughest steel ever known or for the steel that has the greatest wear resistance ever known -- usually without regard to the actual tasks a knife needs to perform. Here's a shot of a blade I had professionally hardened by a well-known expert. He took Benchmade's CMP M4 blade at 59 Rc up to 64 Rc. When I was putting the knife back together, the blade was a bit off center, so I tried adjusting it with just hand pressure exerted laterally against the blade. The blade was so brittle, that it shattered into three pieces. Wear resistance matters. So does toughness.
Things in Italy are even worse.
I made the Sebbie example, I could make more.
610EUR is A LOT of money. I purchased a one of a kind folder from Neels Roos with an M390 blade magnificently HTd. All included (purchase, shipping, customs, VAT) it was less than 2/3 of expense....
Thanks for those thoughts and your expertise, Daberti. I've never used S35VN, so all I have to go on is the experience of others. I, too, would take Elmax and M390 or one of its variants over S35VN, but I have also seen a lot of excellent knife makers swearing by S35VN, even at sub-60 Rockwell hardness. It's difficult for me to believe that Chris Reeve, Sal Glesser, Shirogorov Knives, Spartan Knives and others are so far off on heat treat. Sal, in particular, has shown that he is more than willing to take hardness levels up pretty high and geometry down, especially for knives sold to the general public, so manufacturing costs of a higher heat treat are not the issue.
Chris Reeve's Impofu would be a beast at any reasonable heat treat. It's a giant slab of 3V steel well more than a quarter inch thick. He still runs it at what seems to be for him the sweet spot of hardness: 58-60 Rc. The mystery of that knife for me is what would it be used for. Chris seems to like large knives that are thick. His chef's knife in S35VN was dismissed by some expert reviewers, but not because of the steel or heat treat, but because the blade was too thick.
I watched the YouTube video on which the S35VN Sebenza failed after cutting rope. The whole edge bevel bent over, not just a wire edge. Who knows what that was about, but that experience is certainly not common. Chris Reeve puts a proprietary convex edge on the Sebanza, an edge geometry that he says took him 6 months to perfect. So someone comes along and converts it to a straight edge -- a conversion with well-known risks -- and who knows what happened. We never got a decent analysis of why that blade failed, just another internet legend of a supposedly bad steel.
Do you have any tests or links that you could share that show toughness of S35VN does not improve when the hardness is dropped from 62 Rc to 59 Rc?
There is a tendency for people to look for either the toughest steel ever known or for the steel that has the greatest wear resistance ever known -- usually without regard to the actual tasks a knife needs to perform. Here's a shot of a blade I had professionally hardened by a well-known expert. He took Benchmade's CMP M4 blade at 59 Rc up to 64 Rc. When I was putting the knife back together, the blade was a bit off center, so I tried adjusting it with just hand pressure exerted laterally against the blade. The blade was so brittle, that it shattered into three pieces. Wear resistance matters. So does toughness.
You're welcome mate.
Sebenza wise: I owned the old BG-42 (not PM but very clean for ingot cast technology) made Sebbie and I owned a small Sebbie in S35VN.
The first was a kickass workhorse. Never chipped, never had a wire edge even when I made it straight from convex. And sure the edge stood there longer.
Taking CPM-M4 up to 64HRC can be made with a variety of combinations mate. It depends also on quenching media (salt bath, oil): what quenching media did he use?
Did he follow the CCT timings during quenching?
Did he do air quenching instead?
Most probably he made some mistake in the quenching and/or tempering phase.
From Crucible datasheet..
"Hardening
Preheat: Heat to 1500-1550°F (820-845°C) Equalize.
Second pre-heat stage at 1850-1900°F (1010-1040°C)
suggested for vacuum or atmosphere hardening.
Austenitize: 1875-2200°F (1025-1205°C) Hold time at
temperature: 5-45 minutes. See table. For cutting tools
use 2150-2200°F (1175-1205°C). For cold work applications
use 1875-2125°F (1025-1160°C).
Quench: Air or positive pressure quench (2 bar minimum) to
below 125°F (50°C), or salt or interrupted oil quench to about
1000°F (540°C), then air cool to below 125°F (50°C). Salt
bath treatment, if practical, will ensure maximum attainable
toughness for a given hardening treatment. A fast quench
rate from hardening temperature to below 1100°F (595°C)
is critical to achieve optimum heat treat response. A slower
cooling rate below 1000°F (540°C) may be used to minimize
distortion.
Temper: Double temper at 1000°F (540°C) minimum.
Triple temper recommended when hardening from 2100°F
(1150°C) or higher. 2 hours minimum each temper. (See
Table) Air cool to room temperature between tempers."
Generally speaking the best way of improving toughness without sacrificing edge holding to a great extent, is to use high austenitizing temps/high tempering temps (in the secondary hardening range).
This is what I did with this knife I projected myself for my personal use from a sheet of paper to final product. Elmax @61.5 1080°C/520°C x3
Ankerson
Knife and Computer Geek
- Joined
- Nov 2, 2002
- Messages
- 21,094
Thanks for those thoughts and your expertise, Daberti. I've never used S35VN, so all I have to go on is the experience of others. I, too, would take Elmax and M390 or one of its variants over S35VN, but I have also seen a lot of excellent knife makers swearing by S35VN, even at sub-60 Rockwell hardness. It's difficult for me to believe that Chris Reeve, Sal Glesser, Shirogorov Knives, Spartan Knives and others are so far off on heat treat. Sal, in particular, has shown that he is more than willing to take hardness levels up pretty high and geometry down, especially for knives sold to the general public, so manufacturing costs of a higher heat treat are not the issue.
Chris Reeve's Impofu would be a beast at any reasonable heat treat. It's a giant slab of 3V steel well more than a quarter inch thick. He still runs it at what seems to be for him the sweet spot of hardness: 58-60 Rc. The mystery of that knife for me is what would it be used for. Chris seems to like large knives that are thick. His chef's knife in S35VN was dismissed by some expert reviewers, but not because of the steel or heat treat, but because the blade was too thick.
I watched the YouTube video on which the S35VN Sebenza failed after cutting rope. The whole edge bevel bent over, not just a wire edge. Who knows what that was about, but that experience is certainly not common. Chris Reeve puts a proprietary convex edge on the Sebanza, an edge geometry that he says took him 6 months to perfect. So someone comes along and converts it to a straight edge -- a conversion with well-known risks -- and who knows what happened. We never got a decent analysis of why that blade failed, just another internet legend of a supposedly bad steel.
Do you have any tests or links that you could share that show toughness of S35VN does not improve when the hardness is dropped from 62 Rc to 59 Rc?
There is a tendency for people to look for either the toughest steel ever known or for the steel that has the greatest wear resistance ever known -- usually without regard to the actual tasks a knife needs to perform. Here's a shot of a blade I had professionally hardened by a well-known expert. He took Benchmade's CMP M4 blade at 59 Rc up to 64 Rc. When I was putting the knife back together, the blade was a bit off center, so I tried adjusting it with just hand pressure exerted laterally against the blade. The blade was so brittle, that it shattered into three pieces. Wear resistance matters. So does toughness.
I am sure the maker who did the re-hardening warned you about the issues and risks with re-hardening a blade and that result is the main one...
M4 at 64 isn't that brittle, that is a blade hardened to that level the 1st time.
The problem is going from 59 RC to 64 he had to do the HT whole process on a blade that was already HTed, tempered etc to get the hardness up 5 points... Bad idea and a huge risk as I am sure he told you before he did it.
Now if the blade was in the 62-63 range range he might have been able to go through a tempering cycle or 3 plus a CYRO treatment and the blade would NOT have done that....
Ankerson
Knife and Computer Geek
- Joined
- Nov 2, 2002
- Messages
- 21,094
That's not the problem, the problem was taking a blade that was already HTed and Tempered and running it through the whole process again to get it from 59 to 64 when the chemical changes have already happened the 1st time.....
That's a HUGE risk... HUGE..... HUGE So many bad things can happen and likely will that the risk just isn't worth it..... Better to have a new blade made IMO....
Now what could/should have been done was being it was 59 was to run it through a few tempering cycles as needed and then CYRO Quench it to bump the hardness up to the 61-62 range maybe..... And it would have been fine....
That's something I am sure the maker told the person before they did it.....
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