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I've had my leafjumper in k390 for almost 8 months today and I keep experiencing fairly fast edge wear.

How I'm pretty certain that the edge is good:
→ I've only sharpened it freehand on either 325/400 to 600/1200 grit on both plated and resin bonded diamond stones at 17.4 dps. I would do my best at removing the burr by feeling for it and checking the edge with a microscope and light. I would then strop with alternating passes on a 1µm diamond strop on firm leather for about 4-5 times on both sides. This would almost always result in a hair whittling edge.
→ I also ground down a bit of metal over time, surely removing any burnt/fatigued metal. (the heel is currently 0.020" thick)
→ I was using sharpie on my thumb and pointer finger to keep the angle consistent

How bad the performance was:
→ When I first got the knife, I put my own 600 grit edge on it and cut up about 150' of cardboard. The edge afterwards was so worn, it wouldn't even initiate a slice into printer paper, even after cleaning the edge with alcohol and dragging it on wood to remove any debris blocking the edge. It was as if I dragged it across a brick a few times.
→ Another instance is when I cut no more than 60' of cardboard in 1 week. The cutting consisted of mostly thin cardboard food boxes and thin sheet plastic/mailing boxes. By the end of the week, it could not cut printer paper without significantly tearing or creating a super "fluffy" cut.
→ Even if the edge was never used, the aggression would fade over time
* Something that I think should be noted is that I live a few minutes away from the Gulf in Florida. Also, the humidity here can be anywhere between 55-95% in the warmer months.

How I'm pretty sure my expectations aren't too unreasonable:
This is kind of unrelated to the original post, but I recently got a lw manix 2 in 15v a few days ago. I've decided to use the factory edge (which still has a little bit of burr left) and tried cutting up a lot more stuff and being slightly careless such as making contact with glass jars. The edge is still toothy and sharp and cuts printer paper cleanly.
Edit: the geometry of my 15v manix is 0.025" bte at approximately 20°dps

Thanks for reading my ramblings. Does anyone else have a similar experience with k390? Or am I doing something wrong

A thin course edge will be the best for cardboard
K390 can handle a thin edge
In general, the more you refine the edge (polish) the shorter it’s life will be
15 V is a good step up in edge retention
Geometry out cuts steel

Also from the Florida Gulf area and have had incredible experiences with my k390 stretch 2. Experienced unparalleled edge retention and very little rust when with a patina in place.

Has slowly become my favorite steel.

I do know that a coarser edge will cut cardboard for longer, but even at 600 grit, I feel that it shouldn't be completely dull after a few ten feet of cardboard.
Also, I'm going to edit my post to include the geometry of my 15v manix.

Try an edge that's even coarser than what you've done and see how it performs for you

nope.

I got a k390 police to hold a shaving sharp edge for over a month of edc using a 300 grit edge.

I used the same knife for half a year without any touch-ups and cutting performance remained high.

I typically touch-up a knife after 2-3 weeks of edc for comparison.

K390 is not overrated, in my experience. Last week I cut three legacy phone cables with my 15-degree reprofiled SE Endura in K390 while working in a hot attic. These cuts were in free air at an angle. No edge damage.

Except when talking about corrosion resistance K390 is one of the best knife steels I've tried. It cuts and cuts to the point I have had to make excuses to re-touch the edge. It won't have stopped cutting. The carbides themselves seem to chainsaw through some materials. True that it isn't the only steel I've seen that with. S90V is another that comes to mind as is unmodified 10V/A11 but the thought of K390 being overrated immediately makes me question the OP's sharpening methods and materials.

Every steel is overrated to somebody. I would choose 15V over it if I had the choice, but I don't always have that choice (and likely won't at all in the future). I am however very interested in seeing how MagnaMax turns out if it's supposed to be similar to K390 but also ultra corrosion resistant. I've had a lot of tool steels but so far K390 has been the fastest rusting steel I've carried so there's that. My biggest issue with rust is actually edge degradation, it's pretty annoying to sharpen a knife and then a few days later find that it's lost some of it's bite without even using it.

Evil D wrote: ↑

Mon Aug 04, 2025 7:08 am

Every steel is overrated to somebody. I would choose 15V over it if I had the choice, but I don't always have that choice (and likely won't at all in the future). I am however very interested in seeing how MagnaMax turns out if it's supposed to be similar to K390 but also ultra corrosion resistant. I've had a lot of tool steels but so far K390 has been the fastest rusting steel I've carried so there's that. My biggest issue with rust is actually edge degradation, it's pretty annoying to sharpen a knife and then a few days later find that it's lost some of it's bite without even using it.

fell the same way, K390 is awesome, it overtook M4 as my favorite steel, but now with 15v its replaced K390 for me, but K390 is still incredible, but yep rusts faster than anything else I have where 15v I havent had that issue on the 4 I have at all. When magnacut was all the hype it didnt interest me at all as I didnt really care about something that cuts like s30v but is more corrosion resistant because s30v is stainless enough as is for anyting ive needed and toughness is fine for a folder as well, BUT this new magnamax does have me excited, stainlss k390/10v sounds amazing, petes testing of the mule has it more of a tougher stainless maxamet even as it cut closer to that than k390

Evil D wrote: ↑

Mon Aug 04, 2025 7:08 am

My biggest issue with rust is actually edge degradation, it's pretty annoying to sharpen a knife and then a few days later find that it's lost some of it's bite without even using it.

That is pretty annoying, but it is why I also started using a much coarser edge on tool steels. I first learned that lesson with a Super Blue Caly 3.5. A polished edge is great, but not when it degrades quickly. Super Blue, 52100 and K390 all seemed pretty close to me. Now I generally stop at either 600 or 800 grit stones.

The Mastiff wrote: ↑

Mon Aug 04, 2025 6:42 am

the thought of K390 being overrated immediately makes me question the OP's sharpening methods and materials.

I will admit, my sharpening technique can be a lot better. Is it possible that a very small, undetectable burr on the k390 will initially pop hairs and whittle, but mush over in a few ten feet of cardboard, creating a very dulled edge? I sometimes have problems with the burr not wanting to come off.

Also, sorry if this post is delayed as im still on the probationary period for posting.

mine also rusts, and i also noticed the edge degradation, but keeping it oiled makes all the difference. just tested and still shaves after months in the drawer

vivi wrote: ↑

Sun Aug 03, 2025 9:56 pm

nope.

I got a k390 police to hold a shaving sharp edge for over a month of edc using a 300 grit edge.

I used the same knife for half a year without any touch-ups and cutting performance remained high.

I typically touch-up a knife after 2-3 weeks of edc for comparison.

Gotta figure out what I'm doing wrong because I still can't fathom shaving sharp for a month.

ejames13 wrote: ↑

Mon Aug 04, 2025 2:10 pm

Gotta figure out what I'm doing wrong because I still can't fathom shaving sharp for a month.

I'd be happy just to find a razor blade that stayed shaving sharp for a week.

RustyIron wrote: ↑

Mon Aug 04, 2025 10:09 pm

ejames13 wrote: ↑

Mon Aug 04, 2025 2:10 pm

Gotta figure out what I'm doing wrong because I still can't fathom shaving sharp for a month.

I'd be happy just to find a razor blade that stayed shaving sharp for a week.

I strop my disposable razors and get a month out of them, but I don't shave every single day.

ejames13 wrote: ↑

Mon Aug 04, 2025 2:10 pm

vivi wrote: ↑

Sun Aug 03, 2025 9:56 pm

nope.

I got a k390 police to hold a shaving sharp edge for over a month of edc using a 300 grit edge.

I used the same knife for half a year without any touch-ups and cutting performance remained high.

I typically touch-up a knife after 2-3 weeks of edc for comparison.

Gotta figure out what I'm doing wrong because I still can't fathom shaving sharp for a month.

minimizing the burr, using diamond abrasives, thin edge bevel with more obtuse microbevel, using the knife with care and not striking metal etc. on accident....

Over rated?!!! Get the pitch forks! Get the torches! Burn the heretic!

Seriously, K390 is my favorite non-stainless steel. It holds an edge a long time, but doesn't become difficult and argumentative when sharpening. I can use my Sharpmaker to touch it up. I'm one of those people who can handled a blued firearm and not rust it, so I have no issues with rust on K390. I do put a micro coat of vaseline on my K390, though.

Over rated? No way! I wouldn't call it my favorite, but it's still a great steel. IMO it's a lot like Cruwear but less stainless. I live in Washington State, and it got a patina pretty quick. I don't even carry it that much. Now I just keep a coat of oil on the blade and all is good. No rust to speak of. I agree with some of the other posts that it does well with a more course edge. When I went over 1000 grit it lost it's bite and had a hard time starting a cut. I say anywhere between 400 and 800 grit is where K390 does the best.

Works fine for me , go coarse grit and edge holds up great . I did force patina on my Stretch and use Walkers Wax in humid temps . MG2