Why M398 for high-end knives?

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Twindog

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I've noticed that a number of high-end knives from top makers like Custom Knife Factory and Koenig are coming out in M398 steel. That steel choice makes me avoid those knives because M398 is so low in toughness, making it far more prone to chipping and breaking.

Larrin reviewed M398 and said: "...toughness of M398 is among the lowest I have ever tested." Even ZDP189 is tougher at 3.5 Rc higher hardness.

Bohler designed M398 top be an upgrade from M390, and it does have much more wear resistance, given the bump up in carbon carbides from 17.5 percent to 25 percent and vanadium carbides from 2.5 percent to 5 percent. But those carbides are larger and often connected, lowering toughness by a lot.

M398 has edge wear close to S90V and 10V, but those steels are much tougher. M398 has an edge wear tested at 805 TCC, vs 795 TCC for 10V. MagnaMax has about 770 TCC, but its toughness is 10 ft-lbs vs 2.5 ft-lbs for M398.

I know these high-end knives are more likely to be collection pieces rather than users, but I like to know that my collection pieces have the specs to be great users. So I'm avoiding M398.

Does anyone else feel this way, or am I missing something?
 
I have a Spyderco Mule in M398. I used it a bit and sharpened it with no problems. I certainly didn't expect it to be that weak.
 
I have a small fixed blade in Rex 121 that I use as a dedicated box opener. It works great, but I would never use is as a general purpose EDC.

Did your mule sharpen easily?
 
M398 was optimized for CATRA type cutting tasks requiring maximum edge retention and corrosion resistance. It was never intended for generalized EDC tasks. It excels in this narrow requirement space. I enjoy the M398 blades I have because they sharpen easily, take a wickedly sharp and long lasting edge that responds nicely to a doped strop between stone seasons. If you are missing something it would be that the low toughness was a heads up going in design decision...
How do/would you notices the low toughness? How do you think it affects its design goals? What I’mpoking at is that Rexx 121 would be a poor choice for screw drivers but excels at slicing/cutting tasks just like M398
 
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Really high-end folding knives are more likely to be used regularly but gently, so toughness isn't as critical as edge retention and corrosion resistance. I haven't seen a lot of people have issues with M398 and I kind of doubt that most people would put a ton of force on an expensive folder.

M390 is a great steel but very common now, so I think these high-end brands are trying to differentiate themselves more from those mid-range knives by using M398. For CKF specifically, Bohler has a facility in China that would allow them to avoid import tariffs from using foreign steel. I certainly prefer S90V, but for those specific knives I'm not sure how much more I'd be willing to pay for it.
 
I used M398 in a run of blades specifically for the high wear resistance combined with stainless properties. (It also finished easier than s90v).

That being said, I am unlikely to use it again with the introduction of magnamax.
 
Zylok said:
M398 was optimized for CATRA type cutting tasks requiring maximum edge retention and corrosion resistance. It was never intended for generalized EDC tasks. It excels in this narrow requirement space. I enjoy the M398 blades I have because they sharpen easily, take a wickedly sharp and long lasting edge that responds nicely to a doped strop between stone seasons. If you are missing something it would be that the low toughness was a heads up going in design decision...
How do/would you notices the low toughness? How do you think it affects its design goals? What I’mpoking at is that Rexx 121 would be a poor choice for screw drivers but excels at slicing/cutting tasks just like M398
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I just see it used in high-end EDC knives, almost all of which will end up in collections and never used. I think an EDC should have a reasonable level of toughness to prevent chipping and such. Even if it's a collection knife, it should have appropriate design features, otherwise just use cheap stainless steel. No one would know.

I do use Rex 121, but only for opening boxes. It has a thin blade, an edge thickness of 0.007 inches and a hardness of 70 Rc. I'd never think to use it in an EDC.
 
navman said:
I used M398 in a run of blades specifically for the high wear resistance combined with stainless properties. (It also finished easier than s90v).
Click to expand...

I was wondering about that, all the CKF knives that come with their mirror-polished swedge or are offered in mirror-polished blade variations use M398. That makes more sense now.
 
Another positive for m398 is it seems to sharpen easier than some other high wear resistant steels, and to be honest, if you are looking at that class of steel, then you are, by default, accepting lower toughness.

I have used s90v, s110v and 10v as daily carry small fixed blades for years with no issues. M398 would be no different, it's not ceramic.

I run my s90v at 61-62 hrc and thin bte. Knowing what it can and can't do is important. But as a wise man said...geometry cuts. If the thin edge is too delicate, change the profile.
 
10V would be quite a bit tougher than M398 -- 5+ ft-lbs vs 2.5 ft-lbs -- which is more than twice as tough and more than twice as resistant to cracks and chipping. Of course, it's not stainless.

S125V would have about the toughness of M398, but better edge retention and it is stainless.

S90V is close to M398 for edge retention, but tougher -- 3.5 ft-lbs.
 
M398 is tough enough to cut flesh without breaking but you probably don't want to try to use a baton to break bones with it. LOL! ;)
 
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It has an edge retention rating of 9 on Larrin's steel chart. That is not something to dismiss lightly . 8 on corrosion resistance and 2.5 on toughness.

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I have a couple of M398 Spyderco SpyMytos: one lives in a display case and the other gets used…..very judiciously. Seems to stay sharp forever, really love the kinda’ strange look of it but I’m very careful as to how it is used.
 
I would love to have a user in M398, but all I've owned in it have been a couple of CKFs, and to be honest I'm a little wary of their heat treat.

Maybe that's just me, but I have this weird psychological thing where I hate using knives with thick grinds or soft heat treats.
 
I don't like thick grinds, either, for EDC knives. I have only two CKF EDCs -- a Decepticon 1 and 5.

The D1 has an edge of 19 thousandths on a blade stock of 0.1614 inches.

The D5 has an edge of 25 thousandths on a blade stock of 0.1535 inches.

They are both incredible knives. High fit and finish and drop shut blade.

My Arius, another incredible knife by Koenig, has an edge of 21 thousandths on a blade stock of 0.1563 inches.

For comparison, my ZT 0308 has an edge of 25 thousandths on a blade stock of 0.1560 inches.

These are all high end knives. All are M390. Most EDCs have thicker edges.
 
Thin, acute edges do cut a lot better, but in a low-toughness steel, a thin edge will be even more vulnerable to cracking or chipping.

An edge degrades not just through wear, but also through rolling and microchipping. It's kind of like a three-legged stool. If you have one weak leg, it doesn't help to make the other two stronger. Jacking up wear resistance a lot while lowering toughness a lot, will be self-defeating, unless the cutting tasks are very easy.
 
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