M2 HRC retested and some interesting finds

[Gator97]

Few weeks ago I've tested HRC on 2 knives, Benchmade 710 and Tadatsuna Kamagata usuba. M2 from BM tested 58.8 HRC and Tadatsuna white steel was 62.3HRC.

Needless to say, I was disappointed with M2 being under advertised hardness 60-62HRC.

So, 2 M2 blades from BM 710 went to to Phil Wilson for rehardening, and so did the Kershaw Shallot CPM 110V blade.
Repeated testing showed 59HRC for that M2 blade, which is very close to 58.8HRC, thus I exclude calibration errors. For the record, Kershaw tested 59HRC, which is within 58-61HRC.

Here's what's interesting though. I've had 2 710 folders for EDC use, 710 BT2 coated and 710 BC coated.
BC was the one that tested 58.8HRC.

Now, the interesting part is that the second M2 blade(BT) tested 60 HRC. I've used that blade for around 3 years as my EDC, and the softer 59HRC blade for another 5-6 years.
The way those edges are today: without knowing hardness and assuming they were equal I ended up with ~30 deg. edge on 60HRC and ~40 deg edge on 59HRC knife.

Both M2 blades started out at 30deg angle, using edge-pro. The softer M2 BC, did keep edge worse so I had to make the edge thicker to keep the acceptable edge holding I got used to from the first one. That didn't happen in one day, I figure it took year or so, while I was gradually thickening the edge.

I never did head to head cutting comparison between those two blades. Just EDC carry and whatever cutting that involved. Haven't changed neither my job nor habits either. So, it was pretty uniform stuff.

So, in the end of this long post I just want to say that even 1-1.5 HRC can make a difference for use. Especially long term. I don't know if I'd ever tell the difference if both knives were left at the factory 40-45 deg. edge. Probably not.
However, at 30deg. angle edge, that 1 or so point difference in hardness did manifest in time.

I guess this is my explanation and proof to those who ask why hardness is so important. Yes, I do realize testers have the error margin, hardness isn't the only indicator, etc. But for a given steel, higher hardness did allow me to have a thinner edge, thus better cutting ability.
It was pretty much blind testing from my perspective.

Anyway, I hope rehardened, hopefully 64HRC, M2 will work much better.

 

[sodak]

Very interesting, Gator! 64 HRC M2 will blow your socks off! Great stuff! You will be able to go thinner and a lot longer between resharpenings, I'll be anxious to hear how you like it.

 

[orthogonal1]

Having a couple of my M2 blades rehardened is something I've debated doing for some time.

Lets hear how you like them when you get them.

 

[Gator97]

Sure thing.
I just got the word from Phil Wilson. All 3 blades came out 64HRC. That is 2xM2 for 710 and CPM-110V for the Shallot.

Sharpening all that will be "fun". Especially 110V blade that still has the factory edge, I've sent it to Phil straight out of the box.

 

[gunmike1]

Sure thing.
I just got the word from Phil Wilson. All 3 blades came out 64HRC. That is 2xM2 for 710 and CPM-110V for the Shallot.

Sharpening all that will be "fun". Especially 110V blade that still has the factory edge, I've sent it to Phil straight out of the box.

Now you might want to send them to Tom Krein to regrind the blades so that they are easy to sharpen thin edged slicers. I will look forward to see what your thoughts on the performance is.

Mike

 

[sodak]

Agreed. I have a couple of blades in M2 at 65 - 66, and a knife from Phil in CPM 10V at 64.5. They all are extremely easy to sharpen. They were all ground thin to take advantage of the strength that the hardness offers, and they almost never burr, or burr so little, it's trivial to remove. That's when I have to sharpen them, which is not very often. If you have very thick edges, then it might take a while, but as Gunmike1 said, Tom Krein can easily fix that for you.

You might be pleasantly surprised. I find that the "hard to sharpen" steels are actually the easiest, if the geometry was well done. I spend a LOT more time chasing a burr on AUS 8A then sharpening these high hardness knives.

 

[thombrogan]

Great stuff, Zvi!

One thing stuck out in my head: Do you remember me telling you about Kershaw trying a batch heat-treatment for 13C26 for high hardness? The blades came back oversoftened after getting a BC coating. Your softer 710 makes me wonder if the temperature required for depositing a boron carbibe coating is way too gosh-darned hot for even high speed steels.

 

[Gator97]

Hey Thom I've sent you email last nite. As for the BC being the culprit I thought about that too. Can't say for sure, but bodycote, who did coating for me does that for others as well. Also, BM uses BC coating on their blades. I guess someone would complain by now, but who knows.
I got 2 BM nimravi, both BC coated, sometimes later both are headed for rehardening and I'll get RC test results too. Although, one of them has the edge close to 24 deg and holding up fine.

 

[Gator97]

I have a couple of blades in M2 at 65 - 66, and a knife from Phil in CPM 10V at 64.5. They all are extremely easy to sharpen.

I have CPM-10V and CPM-125V from Phil, one 64HRC, another 65HRC. Sharpening is easy, but grinding new bevel is a major work. I've lowered the edge on 10V blade from ~30-35 to ~22deg. That took few hours or grinding on edge-pro. Since then I got DMT 8XXC and other coarse stones, so it's faster now, but still no candy.

I find that the "hard to sharpen" steels are actually the easiest, if the geometry was well done. I spend a LOT more time chasing a burr on AUS 8A then sharpening these high hardness knives.

Absolutely agree. Harder steels are less hassle when properly used and maintained.

 

[sodak]

I have CPM-10V and CPM-125V from Phil, one 64HRC, another 65HRC. Sharpening is easy, but grinding new bevel is a major work. I've lowered the edge on 10V blade from ~30-35 to ~22deg. That took few hours or grinding on edge-pro. Since then I got DMT 8XXC and other coarse stones, so it's faster now, but still no candy.

Wow! Which knives do you have? I've got the skinner with the upswept point (Coyote Meadow), and the primary grind on it is so thin, I'm surprised that it takes that long. I've spent hours (and wasted a 120 grit stone) on my edgepro taking a CS Trailmaster down like you've described, but I was hogging off *large* amounts of metal...

 

[thombrogan]

I owe you an email, Zvi, and will get to it tonight.

About my blaming the BC-dep process: I think it may be the culprit and also that it doesn't happen most of the time. Maybe batch size or alloy type has something to do with it? Then again, there might've been more complaints from 705BC1CFHS owners back in the day as that was a relatively small batch.

 

[Gator97]

Wow! Which knives do you have?

CPM-10V blade is slightly modified hunter Design from Phil, and 125V is semi skinner meadows, pix and details are here.

Thom, I figure you have a point, because BC coated Benchmades were all 154CM as far as I remember, and M2 blades might've been affected more than 154CMs.

I guess I'll just leave them stripped for now, until I find good coating that won't really affect tampering. Although, these days it's hard to find someone who'd coat knife blade at all.

 

[thombrogan]

Blades get all the coating they need from their own iron and atmospheric oxygen.

 

[Gator97]

I didn't know you were patina fan?

 

[thombrogan]

From the electric blues and purples when they start to the dull brown/gray when they're thick enough, patinas are okay with me.

I doubt M2 will form the patina a lower-alloyed steel forms.

 

[cotdt]

Since the M2 blade was only 58.8 hrc, off from the 60-62 hrc that was advertised, doesn't it count as a defective blade? Benchmade owes me a new CPM M4 blade if my 710-810 turns out to be outside their advertised hardness range, right?

As a side note, I find M2 and M4 relatively corrosion resistant and not really needing a coating. It does develop a patina over time but is quite resistant to pitting rust. The coating scratches, so I'm not a fan. You remove the coating only to find decarburization marks and a rough finish. You end up having to remove a lot of metal for a smooth polish, or applying a coating of your own. Spyderco does not coat their CPM M4 Mule and mine has yet to develop even a patina.

 

[dalee100]

Great stuff, Zvi!

One thing stuck out in my head: Do you remember me telling you about Kershaw trying a batch heat-treatment for 13C26 for high hardness? The blades came back oversoftened after getting a BC coating. Your softer 710 makes me wonder if the temperature required for depositing a boron carbibe coating is way too gosh-darned hot for even high speed steels.

Hi,

It would be very unlikely for a high speed steel like M2/M4 to lose hardness during coating. The very reason for it's existence is it's ability to hold it's hardness and not to lose it's temper to a red heat. And coated HSS tooling is almost industry standard today.

I would suspect that you simply got a blade that didn't hit the mark for heat treat. It happens. Particularly when heat treating batches.

dalee

 

[cotdt]

Hi,

It would be very unlikely for a high speed steel like M2/M4 to lose hardness during coating. The very reason for it's existence is it's ability to hold it's hardness and not to lose it's temper to a red heat. And coated HSS tooling is almost industry standard today.

I would suspect that you simply got a blade that didn't hit the mark for heat treat. It happens. Particularly when heat treating batches.

dalee

Those are my thoughts exactly as the minimum temper temperature for M2 is 540° C, and even this temperature is unlikely to soften the blade. I think it was just too soft originally. Shame on Benchmade. The 13C26 minimum tempering temperture is around 150° C so it is much lower. Shame on Benchmade.

 

[dalee100]

Hi,

I wouldn't say shame on Benchmade. When you heat treat a batch of steel you check a piece or two to see if it's right. If those pieces meet spec, then the rest of it should too. Only sometimes one or two don't. I suspect that like most manufacturer's, Benchmade neither heat treats every blade singly, nor do they check every blade for hardness either. So an OOPS gets by once in a while.

And when you check for hardness, unless you have the surface perpendicular to the ram of the tester, you will get often inaccurate readings. This requires jigs to get the parts surface into proper orientation.

dalee

 

[gunmike1]

Phil Wilson knows what he is doing when he Rockwell tests, so the fact his tests backed up the initial test make me confident that Gator's Benchmade came out soft. Yes, that is the downfall of mass heat treating, but it does suck to be the guy to get the soft blade of the batch. Luckily Gator had Phil to re-heat treat his blades up to some serious hardnesses where they will perform nice. That S110V should be unreal now at 64 RC, and M2 is a beast that hard as well.

I recently sent 5 of my blades to Phil for testing and all were in the range they should be or harder. My 154 CM Benchmade Rift was 61 RC, my CPM D2 Spyderco Millie was 62, my M4 Mule was 62.5, my Stretch ZDP 189 was 64.5, and my S90V Manix 2 was 58/59. It was interesting getting those readings back on the 154CM and the CPM D2 because both steels perform great, taking very crisp edges and holding them a good time for what the steel is. Gator's experience of having a 1 point difference cause him to have to raise his angle significantly is not surprising to me. For instance I wasn't expecting much from my Rift after working on one of my in-law's 154CM blades, but as soon as I sharpened and used the Rift I could tell the steel was good stuff. No burring or rolling, just nice crisp sharpening and cutting. The CPM D2 Millie has always outperformed S30V for me and taken a tremendous edge, and the extra 3 RC points over S30V knives I have helps to explain that. The S90V Manix 2 blows me away with how long it can slice for, but knowing I could have it re-heatreated another 2-3 points harder is tempting. Then again the Manix 2 is a HD cutter, and I don't know if sacraficing toughness for the extra edge retention is worth it. Considering I don't plan on chopping down trees with it I may just push the limits of what the steel is capable of, but I must say as is Spyderco did an excellent job with it considering the intended use of the knife.

Mike