M390 edge retention properties

dkb45

dkb45

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I've used a fair bit of M390 (and half brothers like 20CV and 204P) and noticed they all have odd properties when it comes to dulling. They all seem to wear like S30V, at least for me, very fast dulling of the keen edge then long holding of the working edge. Is this an issue with my sharpening, how the steel acts, or is it M390 specific to cutting an abrasive media like cardboard (what I mostly cut at work)? I've found steels with overall lower edge retention seem to hold their keen edge a lot longer, like ZDP-189 and Elmax. CPM-154 also put up a really good showing.

I'm also getting a lot of deformation of the apex, like slight curling almost like a burr is forming, but I fully refine each grit and knock the burr off in sharpening. This has happened fresh off the stone, stropping with diamond compound, polished and toothy edges. Does this steel just have weird properties?
 
My Ritter Griptillian is the only M390 I have used a heck of a lot and I find it to hold a fine edge.
On the order of CTS-XHP but longer and better.
The edge geometry on the Ritter was just really nice from the factory so I have used it a lot and not had to sharpen it much. This was on my gold standard test : trimming kind of abrasive hard rubber. The only steel I have that has ever done better at this is M4.

So I would say something is going on with your sharpening or the heat treat is not as hard as what I have. I have always sharpened my M390 to a polished edge 4000 Shapton Glass on the Edge Pro for push cutting.

IMG_3743.jpg

Never any significant cardboard with this knife. I so much prefer a super thin blade for cardboard which in my case is almost always double wall corrugated and boxes on the order of 54 inches long.
Stock Stanley fixed box knife blade is king : 0.40mm ! ! ! !
Top knife in photo below. I put the fixed / non retracting Stanley blade in this folding box knife but you can see how it isn't as long and doesn't fit as well. Sure is thin though ! ! !
Re profiled and polished no less. Sure it dulls but it still keeps cutting like a motha.
= another case of geometry trumping alloy.
This Stanley stuff can't hang in the rubber trimming though. It goes down in flames quick.
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Everything I’ve read about M390 states that to get the best performance from the steel, the edge angle should be at 15 degrees per side. Less than that is where issues come in. I typically stay with factory edge angles because sometimes I’m rough on a work knife. I don’t pay much attention to how sharp a knife is through out the day other than if it still cuts without much effort. I don’t cut a lot of abrasive material daily, but if I’ve got to cut up any amount of cardboard, I like to use a razor knife or a thin blade fixed. I’ve dulled my pocket knives cutting appliance cardboard packing with one usage. I try not to do that anymore.
 
I've considered an answer, typed it, erased it. The best fella I know that cuts a ton of cardboard is our buddy, Ankerson.
When you need to KNOW...go to the PRO.
 
Well, since i'm cutting cardboard containers 0,4" thick pretty much every day with a mora flex and didn't have to sharp it in a week, i would be surprised to see how the same knife in m390 would handle...
 
I've found the same myself. The fine hair popping edge doesn't last long at all though it's easy enough to restore. The regular edge lasts a good long while. I don't like it to be honest. I'd expected the keen edge to last far longer given the reputation of the steel and I like a keen edge on my EDC specifically for zipping cleanly through packaging. The hair popping edge I've had on 154cm and even D2 surpasses it. I've never tested the regular edge longevity though we have plenty tests to show just how good it is.
 
Pomsbz said:
I've found the same myself. The fine hair popping edge doesn't last long at all though it's easy enough to restore. The regular edge lasts a good long while. I don't like it to be honest. I'd expected the keen edge to last far longer given the reputation of the steel and I like a keen edge on my EDC specifically for zipping cleanly through packaging. The hair popping edge I've had on 154cm and even D2 surpasses it. I've never tested the regular edge longevity though we have plenty tests to show just how good it is.
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This is my experience. One steel that surprised me though was S30V with a full diamond progression, toothy or refined it held the edge so much longer than I am used to if you use it straight off the stone or strop with diamond too. No deformation of the apex, no razor edge dulling at light speed, it made it a proper linear dulling.

Honestly I've been kinda shocked at how M390 loses the shaving sharp edge. For a steel with such insane edge retention, I'd expect the razor edge to last longer. One steel that really shocked me was K390, I cut a literal grocery cart full of cardboard up with it and the edge was still catching hairs. That steel is supposed to prefer a toothy edge but it held the keen edge like a champion. Really wish it was used more often, it almost made M4 look bad in edge retention on a linear dulling scale.

It sounds like M390 is a great steel, but not the holy grail for my needlessly picky specific set of traits I'm looking for. It's basically S30V without diamonds but better in most ways.
 
Juicytarget said:
Well, since i'm cutting cardboard containers 0,4" thick pretty much every day with a mora flex and didn't have to sharp it in a week, i would be surprised to see how the same knife in m390 would handle...
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How much cutting everyday?
 
dkb45 said:
I've used a fair bit of M390 (and half brothers like 20CV and 204P) and noticed they all have odd properties when it comes to dulling. They all seem to wear like S30V, at least for me, very fast dulling of the keen edge then long holding of the working edge.
Click to expand...
I had the exact same experience with M390. It lost its keen hair shaving edge very very quickly but kept a working edge a long time. I wasn't impressed with M390 and actually prefer S30V over M390.
 
I don't see what the problem is. Are you shaving with it on a regular basis? If it holds a working edge for a long time, isn't that the main thing?
 
Super keen edges (like hair popping) will not last long regardless of the steel brand. What matters the most is a long-lasting working edge (like slicing print paper without tearing).
 
My only example of M390 is the Kershaw Dividend. I'm not sure the hardness is where it should be, but it is pretty easy to sharpen and maintain on a strop. I agree with OP on how the edge loses shaving sharp quickly but keeps a good biting edge for a long time. I have actually been most impressed with S35VN in terms of keeping a shaving edge for awhile and also being able to quickly get that edge back when it does deform.
 
Did you remove the old edge full of damaged steel first? Did you apex with too coarse a grit with your first stone?

Its possible you may of had a very small bur that's too stubborn to remove or notice. Maybe it formed from the stropping.

What edge angle, stones, and grit progression? What knife also?

Could be anything really.
 
I can't say the edge angle, because I use an Aligner but clamp the blade closer to the spine. Most of my angles eyeball to be about 30° inclusive though. My progression is XXC, XC, C, M, F, EF, and Venev 2/3 micron. My methods are to marker the edge and work it all off with the new bevel using XXC on both sides, then go to XC and raise a burr on both sides along the entire edge (checking the apex in the light to make sure the whole apex is formed). Then I go to C and work the apex on both sides. Next M, and after I raise the burr in both sides I make another pass with much lighter pressure to simulate a middle grit. Same with F. On EF I do 3 total sets, one with normal pressure, one with medium pressure, and one with feather weight. On EEF I do the same, sometimes doing a 4th pass with as little weight as I can possibly apply. The aether weight pass is usually always edge trailing.

I always use a light scrubbing method for my sharpening. I lubricate the stones with (don't laugh, it works) water based "personal lubricant". After the Venev I will usually strop with 3.5 micron then 2.5 micron.

When I do a toothy edge, I do the same thing up to the F, and do 3 burr raises with decreasing pressure like I usually do on the EEF. Then I strop on 40 micron then 20 micron..

It's weird, because only M390 acts up like this. M4 to a lesser extent, but I know that steel prefers a toothy edge.
 
sharp_edge said:
How much cutting everyday?
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Like i said, it's mostly 0.4" thick cardboard, and depending on the day, i can cut from 1 to 3 boxes that are (sorry i'm a EU Guy) 1x1,5x0,8m.
(I'm the fastest guy at cutting thanks to the mora so they give me all the containers)

I cut them in 0,30x0,80m pieces in order to make clean packages.

The flex is my only knife cutting with such ease cardboard, but because of the thickess it's heating a lot by friction and i think i'm somehow ruining the HT.
 
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