Blade Steels

[Whoever Wherever]

I believe that M4 looses its toughness edge after 61Rc from initial reports from people using it in cutting competitions. The whole point of using CPM-M4 is to not have to choose between toughness and wear resistance, so hardening to 65.5Rc would seem to be counterproductive. I do not know what pounds it gets at 60Rc but from everyone who is hardening it to that, it has no issues bieng slightly underhardened form specs. Ed Tarney, metalurgist from Crucible says that 59-61Rc is best for blade purposes.

Jay, I have to say I hate Aus-6 and could care less how sharp it becomes. Every knife I have owned in aus-6 have bad blade dammage from normal use. You mention S30V chipping but Aus-6 chips much worse imo.

 

[thombrogan]

The whole point of using CPM-M4 is to not have to choose between toughness and wear resistance, so hardening to 65.5Rc would seem to be counterproductive.

If you don't have to choose, then why run it softer? Wouldn't the whole point of CPM M4 and ingot M4 be for high-heat/high-friction industrial applications in which edge-angles thought too thick for kitchen knives would be adequate for the machine performing the cutting? Why not get some O7; ignot cast or powdered; and get the higher edge stability of M2 without all of the heat-treating hassles that delicious molybdenum adds?

 

[Whoever Wherever]

You run it softer for the best combination of traits, in industrial aplications the harder Rc probably is a benefit on blades that will never be sharpened and will just be replaced when worn. In knife making there is always trade off between different traits you want from the steel. 07 I am not familiar with. There is probably a good reason it isnt considered the "new steel to use". I do not know enough about it to comment at all on its use. The only way you dont have to choose between toughness and wear resistance with CPM-M4 is if you harden it right. In this case for a knife blade. Its not hard to find a steel that wont break, or that cant be sharpened its so tough, or one that will get razor sharp but chip and break. M4 seems to have all characeristics in proper proportions (except corrosion resistance) and can still be sharpened at home or in the field. You want to run any steel at the hardness best suited for its purpose. I do'nt think Crucible would recomend underhardening it if it wasnt a good idea. You can take M4 to a higher hardness but it wont have the same toughness.

Someone else will have to chime in about 07

 

[thombrogan]

You run it softer for the best combination of traits

Have you ever used one of those ZDP-189 blades in knives made by Kershaw, Spyderco, or William Henry? I've got one from Spyderco and it stands up to normal use and is easy to sharpen when it eventually dulls. Its hardness is between 63-64 on the RC scale and it's a stainless steel. I've got a Fallkniven brand U2 which has Takefu's SGPS hardened slightly softer (RC62) and it's stainless, too. Ever look at Japanese-style cutlery? A lot of nice knives out there with hardnesses of RC65-67 (non-stainless and stainless) and they cut hard-on-edges stuff all day long without complaint.

You can get one of those U2 knives for about $50 or so or a Spyderco Delica with ZDP-189 for about $70 or so (I recommend the ZDP Delica) and see what I mean. Hardness is what lets you take an edge down real thin without it crumpling so you can cut for cutting's sake instead of muscling through something.

In knife making there is always trade off between different traits you want from the steel. 07 I am not familiar with. There is probably a good reason it isnt considered the "new steel to use".

It sure is a good reason, too, but there are several steels out there which would rock for pocketknives (even 'tactical folders'), but continue to be used for other applications.

M4 seems to have all characeristics in proper proportions (except corrosion resistance) and can still be sharpened at home or in the field.

How do you know this? All's I know about O7 is that it's M2 without all of the moly. I use M2 more often because there's a guy who sells fully hardened M2 hacksaw blades for a good price and anyone, even me, can regrind them into a good knife without having to bother with a heat treatment. M2 has fairly good corrosion resistance compared to other nonstainless steels, so M4 may even have more.

I do'nt think Crucible would recomend underhardening it if it wasnt a good idea. You can take M4 to a higher hardness but it wont have the same toughness.

At what hardness range did they recommend? I've seen some of their sheets showing comparisons to other steels, but the M4 was at RC64 (less dulling from rolling; less dulling from wear; possible more dulling from impact; more demanding of a heat-treater's furnace; edge likely to be less stable at really low angles, but maybe not).

For all I know, M4 will be as good as or better of a knife steel as you say; we'll see soon enough. Until then, buy or borrow a ZDP Delica or Fallkniven U2 and see why high hardness is very nice (kid-tested/mother-approved) for tac folders and other pocket knives. You can get a high-quality 1200 grit diamond sharpener from DMT or EZE-Lap for barely anything ($6-10 for a DMT mini-sharp) if you need to quickly restore a hair-popping edge away from home on any non-serrated knife.

 

[Cliff Stamp]

Has Alvin ever considered CPM-M4?

He used a higher carbide HSS and had problems obtaining a high polish as the edge micro-chipped. This would be expected as the edge stability decreases with increased carbide volume. P/M vs ingot does really make a significant difference there though it does in other areas such as fracture toughness in gross samples and it will improve edge consistency as otherwise you get high/low spots due to carbide irregularities.

Why not get some O7; ignot cast or powdered; and get the higher edge stability of M2 without all of the heat-treating hassles that delicious molybdenum adds?

The main issue with those grades from an industry viewpoint is warping when heat treating. There is also the fact that multiple high tempers to reduce retained austenite is easier/cheaper than multiple low tempers/cold especially when you are working with complicated shaped parts which you can't just jam into liquid nitrogen. Multiple high tempers on steels like O7 just make really wear resistant springs so it isn't an option for them. Of course for the price you pay for high end custom cutlery the complexity of the heat treatment should not be a limititation.

In regards to wear resistance for the cutting competitions, the cutting volume is so low that wear resistance isn't a factor. As Thom noted, the extra hardness would allow for a finer cutting edge because the steel would be stronger. The only concern would be if the steel was too brittle at that level which would suggest a lower carbide steel which would be inherently tougher at a higher hardness.

The hardness of steel also doesn't limit ease of sharpening, even the hardest steel is pretty much butter to any quality stone, even waterstones will peel 65 HRC M2 like a wood rasp on pine. Carbide volume is more of an issue with sharpening and underhardening actually makes it worse because you increase burr formation.

-Cliff

 

[Larrin]

I believe that M4 looses its toughness edge after 61Rc from initial reports from people using it in cutting competitions. The whole point of using CPM-M4 is to not have to choose between toughness and wear resistance, so hardening to 65.5Rc would seem to be counterproductive. I do not know what pounds it gets at 60Rc but from everyone who is hardening it to that, it has no issues bieng slightly underhardened form specs. Ed Tarney, metalurgist from Crucible says that 59-61Rc is best for blade purposes.

But Alvin doesn't make chopping knives, he makes very thinly ground high hardness knives. You do get greater toughness with 59-61 Rc, but 20 ft. lbs. is about what D2 and M2 get at 60 Rc, and that's CPM-M4 gets at 65.5 Rc. Like anything, you modify the heat treatment for the application. BTW, Gayle Bradley has a chopper in CPM-M4 at 62 Rc. The higher hardness brings both higher wear resistance and more resistance to rolling at the edge, or "micro rolling". CPM-M4 toughness:

Rc........Charpy C ft. lbs.
65.5.......20
63.5.......28
62.........32

Ed Tarney also says that CPM-M4 is not quite as tough as A2 but 95% (or so) of companies that switched to CPM-M4 from A2 for higher wear resistance didn't experience any toughness problems. So for 60 Rc, that would put it somewhere between the 32 ft. lbs. it gets at 62 Rc and the 40 ft. lbs. A2 gets at 60 Rc.

 

[Cliff Stamp]

But Alvin doesn't make chopping knives, he makes very thinly ground high hardness knives.

He makes chopping knives, just not out of HSS. They are also very thinnly ground and still very hard. He is making one now for me to evaluate, full hard edge, spring spine, bandsaw steel.

-Cliff

 

[Larrin]

He makes chopping knives, just not out of HSS. They are also very thinnly ground and still very hard. He is making one now for me to evaluate, full hard edge, spring spine, bandsaw steel.

-Cliff

I guess I don't know much about him.

 

[Cliff Stamp]

This is fairly recently, he used to for a long time (20 years) just make really deeply hollow ground blades. Lately however he has been experimenting with flat/convex grinds and larger chopping blades. But the same constraints are there, maximum cutting abilty / edge retention / sharpness. The edge configuration on the large chopper will be thinner and more acute than the vast majority of small folders.

-Cliff

 

[Whoever Wherever]

Have you ever used one of those ZDP-189 blades in knives made by Kershaw, Spyderco, or William Henry? I've got one from Spyderco and it stands up to normal use and is easy to sharpen when it eventually dulls. Its hardness is between 63-64 on the RC scale and it's a stainless steel. I've got a Fallkniven brand U2 which has Takefu's SGPS hardened slightly softer (RC62) and it's stainless, too. Ever look at Japanese-style cutlery? A lot of nice knives out there with hardnesses of RC65-67 (non-stainless and stainless) and they cut hard-on-edges stuff all day long without complaint.

I never said that a high Rc is bad for knives or that it is a bad thing in M4 and never suggested all steels would fall into the parameters that I was talking about when hardening M4. I was commenting on hardening M4 because someone asked about hardening it. ZDP is from what I've heard a great blade steel. That doesnt mean nothing is outpreforming it. Yes alot of Japanese Cutlery is hardened to a very high Rc. As a chef of a deacde who had s run a kitchen I can tell you this is for specific work and they would break under European knife use. (hacking through bone ect...) This is not to say that Japanese kitchen knives are without there choppers. But they are not hardened to that Rc. The high Rc knives are usually chisel ground to a zero edge and are for thin slicing.

You can get one of those U2 knives for about $50 or so or a Spyderco Delica with ZDP-189 for about $70 or so (I recommend the ZDP Delica) and see what I mean. Hardness is what lets you take an edge down real thin without it crumpling so you can cut for cutting's sake instead of muscling through something.

If you think that the edge on a properly made M4 blade needs to be muscled through a cut or that it doesnt have a thin enough edge you must have never used one. Also you must have missed Gayle winning the 2006 Guild cutting competition with it. While I do think that these competitions are as much about the cutter and his skill/strength you simply will not win one with anything but a razors edge that holds the whoel competition. In short regardless of ZDP M4 is not at all disadvataged by a lower Rc.



It sure is a good reason, too, but there are several steels out there which would rock for pocketknives (even 'tactical folders'), but continue to be used for other applications.

As I said I cannot comment on 07. However I think someone aswers your question below your post.


How do you know this? All's I know about O7 is that it's M2 without all of the moly. I use M2 more often because there's a guy who sells fully hardened M2 hacksaw blades for a good price and anyone, even me, can regrind them into a good knife without having to bother with a heat treatment. M2 has fairly good corrosion resistance compared to other nonstainless steels, so M4 may even have more.

Like I said in my earlier posts I am waiting on some M4 to try out myself. I have cut with one while noting for my own curiosity how well I thought it preformed. All the rest of what I know is taken from much better and more experienced knifemakers than me who started using the steel first. M2 is from what I know a good for knife making although I have not used it myself. I live in Alaska and try to buy steel that I can get in state so I dont have to ship it. The guy I go to does not carry everything so I only order steel form out of state if I really want to play with it. M4 falls into that catagory and I think its worth a look to anyone.

At what hardness range did they recommend? I've seen some of their sheets showing comparisons to other steels, but the M4 was at RC64 (less dulling from rolling; less dulling from wear; possible more dulling from impact; more demanding of a heat-treater's furnace; edge likely to be less stable at really low angles, but maybe not).

There spec sheets for the steel are designed around its original use and therefore may not represent the best hardening specs for a knife. Scott Devanna, Crucible District manager related the suggested rockwell to Dexter Ewing who printed it in Blade for whom he is a field Editor. The knife makers who are working with it seem to agree with this analysis. At the prices it goes for I will take there advice and use there recomendations along with excepting there explanation and the results seen in the knife I used and the one used to win The competition. When I have money to spare and I am on the edge of each new steel as its comes into play in the knife world I will want to play with the hardness of most any new steel I get to decide for myself what Rc it is best hardened to. But until then I'll be happy to let others do initial experiments and listen close to what they learned. As it is I still have a range to harden it within to experiment with and find my own personal "sweet spot". I only suggested that the extra hardening would bring you out of the sweet spot between toughness and wear resistance because I was told this and have experienced the same phenomenon on other steels even if the Rc in question was different. I figure if I can get proper edge hold and sharpness at 61Rc theres no reason to go higher if it will reduce its impact resistance.

For all I know, M4 will be as good as or better of a knife steel as you say; we'll see soon enough. Until then, buy or borrow a ZDP Delica or Fallkniven U2 and see why high hardness is very nice (kid-tested/mother-approved) for tac folders and other pocket knives. You can get a high-quality 1200 grit diamond sharpener from DMT or EZE-Lap for barely anything ($6-10 for a DMT mini-sharp) if you need to quickly restore a hair-popping edge away from home on any non-serrated knife.

I'm not really shopping for a new folder (although theres a few im looking for ), but thanks for the advice. I know a high hardness is nice and underhardened knives in general suck. I am not talking about any steel though. M4 is a tough steel that from what I hear grinds in an annealed state like a hardened steel. I sdont think those few Rc points are anywhere near making this a soft blade at 61Rc. The fact that it is so hard to work with will keep production companies away from it most likely. It will be a hot shot steel that works great and then Crucible or someone else will give us something better (starts tapping foot =P ). I want to work with it because it outright impressed me and from what I have heard I am not the only one. Am I buying into a marketing ploy for expensive tool steel? Maybe, I fully admit it. I havent had a knife made from it in my hands long enough to make an real stand for it. But I think this one may be "it" for however long its 15 mitnues of fame last. The best blade steel is always dethroned and rarely agreed upon anyways. But the thread asked what we thought the best blade steel and if the edge and edge holding I saw really has the durability and length of edge retention that winning one of the big knife cutting competition must require then it gets my vote for the time bieng. If I get it and hate it I will come back and eat soem crow pie. But I may just end up with a ZDP blade to boot and then I can see if its worth the extra money and grinder belts. Often the difference in good blade steels isnt as much as we like to pretend, but like I said, this steel inpressed me.

This thing messed up my qoutes, lol. I have to get some sleep but I'll try and clean it up in the morning if anyone cares. Just my .02 anyways so dont take me to seriously. Also I will fix my spelling. Those beers have not done wonders for my typing.

Also from Larrins' post it seems they are finding 62Rc to work well. so 61Rc may have been a little low for the ceiling.

 

[db]

Big Jim said...
"Often the difference in good blade steels isnt as much as we like to pretend,"

I'd have to agree with that. Without side by side comparing in normal use the noticeable difference is close to zero.

 

[JayAndersson]

Jay, I have to say I hate Aus-6 and could care less how sharp it becomes. Every knife I have owned in aus-6 have bad blade dammage from normal use. You mention S30V chipping but Aus-6 chips much worse imo.

Really, it like my knife in AUS 6, although it's was one of my first knives so I had little to compare with. Mine worked fine, no chipping. I treated that knife with (too much?) care, so it was never really put to the test. Still I loved the knife.

 

[Maqua]

I have a big, shiny Al Mar Quest III in AUS-6. I love it, it takes a very nice edge, or edges, but I have never chopped anything other than my back hairs. It would probably shatter like Britney Spears' panties being tossed from a Bentley.

 

[Cliff Stamp]

I sdont think those few Rc points are anywhere near making this a soft blade ...

Few people would contend that the softer production knives at 54-56 HRC are not very different than the production and custom knives at 58-60 HRC. In fact these differences are so extreme that this 5 point change in HRC moves the knives from "junk" to "excellent". Now of course there is more to performance than hardness, but for the moment just consider that attribute.

Now if this is judgment is accepted as reasonable, then consider that most cutlery steels (outside of the japanese ones anyway) can actually be made about 5 points harder than they are usually ran. This would imply that the exact same comparison could be made about what they are compared to what they could be.

It would also directly indicate than even changes of 1-2 HRC points would not be an insignificant matter because you are looking at roughly half of the distance from junk to excellent. Now again, there is more to a steel than the hardness, but there is no way changes of 1-2 HRC points can be labeled as trivial and still accept changes of 4-5 as overly significant.

-Cliff

 

[hardheart]

I tend to look at it as trying to balance qualities. If you can get a certain toughness, edge stability, corrosion resistance, etc. at a certain Rc hardness, and on balance it outperforms other steel choices in these areas in a way that is proportionate to any increase in cost or requirements for maintenance, then that is improved, although maybe not 'optimal' for that steel.

Like with the mention of A2 and M4. I don't have any experience in such a compariosn-but if M4 can approximate A2s impact toughness and provide a higher edge stability, match the corrosion resistance, or cost about the same to produce or purchase, then it is a better choice than A2 when hardened to 62 or such. You can go harder with the steel, but then does it suit the intended use of the blade design for which it is being used. If not, then another steel could be used. Of course, you now have to ask yourself again-is it better to use a different steel, or to just harden the M4 a few points lower-what are the differences in cost and performance.

This is maybe sort of looking for a wonder steel, one that you could use in small, thin, pure cutting instruments with one heat treat, and then turn around and put in a heavy chopper with another HT. If this could allow a producer to stock and order one type of steel, grind it with the same equipment for all patterns before heat treat, and more easily control HT for the different applications, that would be good for them. I'd guess. I don't know which is really more economical-it might be better to stock a couple different steels that perform differently with very similar HT, to keep that process consistent. But I don't know if anyone does that either.

 

[Larrin]

Like with the mention of A2 and M4. I don't have any experience in such a compariosn-but if M4 can approximate A2s impact toughness and provide a higher edge stability, match the corrosion resistance, or cost about the same to produce or purchase, then it is a better choice than A2 when hardened to 62 or such. You can go harder with the steel, but then does it suit the intended use of the blade design for which it is being used. If not, then another steel could be used. Of course, you now have to ask yourself again-is it better to use a different steel, or to just harden the M4 a few points lower-what are the differences in cost and performance.

Don't forget ease of sharpening. M4, though, is not easy to sharpen.

 

[Whoever Wherever]

Actually the couple people I've talked to have all said that CPM-M4 is easy to field sharpen with standard sharpeners. It may not shapren on a strop alone (most knives wont but it does take the burr off) but from what I know of steel like S30V you are out of luck in the field. I have been told first hand that ceramic and diamond sharpeners both do a great job on M4. From what I understand the metal eats belts because it has an abrasive quality and is rather hard, but trimming of the edge to sharpen is not hard ( not shure if its rough on the stones). When i first read about m4 I thought it would be hard to sharpen, but thats one of the selling points bieng pushed is ease of sharpening. Ill have to chime in about this after i play with some. Right now I'm taking peoples word it sharpens easily. I have seen it cut though and that it does in spades.

 

[Larrin]

Actually the couple people I've talked to have all said that CPM-M4 is easy to field sharpen with standard sharpeners. It may not shapren on a strop alone (most knives wont but it does take the burr off) but from what I know of steel like S30V you are out of luck in the field. I have been told first hand that ceramic and diamond sharpeners both do a great job on M4. From what I understand the metal eats belts because it has an abrasive quality and is rather hard, but trimming of the edge to sharpen is not hard ( not shure if its rough on the stones). When i first read about m4 I thought it would be hard to sharpen, but thats one of the selling points bieng pushed is ease of sharpening. Ill have to chime in about this after i play with some. Right now I'm taking peoples word it sharpens easily. I have seen it cut though and that it does in spades.

I've heard the same reports. It may me easier to sharpen than S30V, but it's definitely not like carbon steel.

 

[Whoever Wherever]

I've heard the same reports. It may me easier to sharpen than S30V, but it's definitely not like carbon steel.

No, I dont suppose it will be as easy as carbon. But the fact that you can just stone it is a nice change over S30V. I am really curious to see just how "easy" it is. Maybe in 10 more years we will have a steel that clearly outpreforms the rest but then we'd miss out on all this fun =P

 

[Whoever Wherever]

Really, it like my knife in AUS 6, although it's was one of my first knives so I had little to compare with. Mine worked fine, no chipping. I treated that knife with (too much?) care, so it was never really put to the test. Still I loved the knife.

Yeah I dont know about Aus-6. The thing is that all my dammages aus-6 blades are on Spyderco knives that have a full serration pattern. Therefore the blade dammage is usually in the serration scoops and not the points. Prehaps it preforms better in a non-serrated blade. I do know that I will stay away from it from now on. I am not putting down Spyderco, I just should have bought models they used better steel in.