Corrosion and Edge Retention

[aaronkb]

Hi all,

I’ve always operated on the assumption that corrosion is a primarily aesthetic issue. I don’t care much about stainlessness, and don’t bother oiling my knives. I like tool steel performance and a clean blade (honestly I hate handling anything that’s sticky or oily, not sure which is worse).

I’ve noticed, however, that some of my least stainless knives appear to go dull just by sitting on the shelf for a couple weeks. The primary culprits are k390 (especially seki k390, which I believe is run harder and less corrosion resistant) and m4, which are two of my favorite steels otherwise.

It was something I vaguely noticed living in DC, which is a pretty humid environment. I recently moved to San Diego, which is even more humid as well as salty given the proximity to the ocean, and I feel like the issue has become undeniable.

So I’d like to pose the question to what I consider an extremely knowledgeable community: do you all find that corrosion can noticeably deteriorate a knife edge over time, especially in high-humidity and salty environments? Or am I crazy? If I’m not crazy, is there a solution that won’t leave my knives and everything I cut with them feeling oily to the touch?

[phaust]

I definitely notice a difference as you say. The fine edge leaves fast in humidity.

My solution was to switch to more corrosion resistant steels. I think it would be hard to apply something to the edge that would stay there through use, and reapplying every time it gets used just isn't something I'm willing to do.

[aaronkb]

I definitely notice a difference as you say. The fine edge leaves fast in humidity.

My solution was to switch to more corrosion resistant steels. I think it would be hard to apply something to the edge that would stay there through use, and reapplying every time it gets used just isn't something I'm willing to do.

Ugh…. I was really hoping to be contradicted, not vindicated! I don’t want to give up my favorite steels. At least my rex 45 has been behaving. And I could maybe convince myself to jump on the cruwear bandwagon.

[Bolster]

do you all find that corrosion can noticeably deteriorate a knife edge over time

Welcome to So Cal!

That's my impression. Living near the coast, knives will go dull in the drawer. However, I have never tested for a difference in "drawer dulling" between stainess vs tool steel--don't have a good method of doing so. But it would stand to reason that stainless blades would keep an edge longer in humid/salt environments.

I knew a guy who would run his blades across a candlestick after sharpening, to wax the edge, but that was never tested with a control group either. Another solution might be storage in an airtight case with cannisters of dessicant. I'd hope you could find a workable solution rather than give up your favorite steels! I'm sure solutions will roll into this thread.

[vivi]

no issues where I live. pretty humid and hot in my area even if I'm not that close to the coast.

I recently went through my folders and sorted them by ones that are sharp with no play and ones that need touched up or some pivot tweaking.

My K390 Police with pakkawood scales was among the ones that were plenty sharp, along with my Rex45 Chief and M4 Manix XL.

I work as a chef and my most frequently used knife is a white #1 6" pretty. Very reactive steel. I can slice 12 tomatos and the primary grind will be spotted yellow before the job is done. I slice all sorts of reactive food with it regardless, like lemons, limes, tomato, pickled foods etc.

Even with obvious corrosion building up multiple times per night, spots of actual rust on top of the dark patina, the edge stays sharp the entire shift. And when I say sharp I mean touch the skin of a tomato and it parts sharp, the upper end of what we talk about when we discuss sharpness.

I take my culinary knives to much higher degrees of polish and sharpness, and consistently expose them to corrosive foods every day, so I'd see this sort of things pretty fast I'd imagine.

Aogami Super is a lot more corrosion resistant. It's formed dark patinas but zero issues with the edge.

It may just be your environment but I've never encountered this. That k390 police was sharpened to 200 grit last time and it still shaves.

[standy99]

Live in tropical Northern Australia and a M4 user and have never had a issue with a dulling while the blade is sitting. Blades usually aren’t used for the wet season
Maybe just a swipe or two on a steel after storage.

Trick I have used on all knives before storage is a bit of mineral oil on a rag and wipe and drag the blade across a cheap candle or crayon. (As mentioned above)

[aaronkb]

I take my culinary knives to much higher degrees of polish and sharpness, and consistently expose them to corrosive foods every day, so I'd see this sort of things pretty fast I'd imagine.

Actually, I think higher polish —> more corrosion resistance so you just gave me an idea to try

[vivi]

I take my culinary knives to much higher degrees of polish and sharpness, and consistently expose them to corrosive foods every day, so I'd see this sort of things pretty fast I'd imagine.

Actually, I think higher polish —> more corrosion resistance so you just gave me an idea to try

On the side of the blade, yes.

On the bevel, yes.

On the apex, I would imagine no.

Higher polish edges are thinner at the very apex, so any degradation will be more noticeable.

Taking a knife to 8,000 grit and dulling it until it can't shave it will barely slice certain materials. Taking a knife to 200 grit than dulling it until it can't shave the difference in cutting ability is not perceivable outside controlled testing.

I could be wrong, but I would expect this to affect polished edges faster.

[Evil D]

I remember talking with Lance about edges going away due to corrosion, and it's something I've experienced over longer periods of time when I have non stainless steels put away in storage, for example my 52100 never has the same bite when I bring it out as it did going in, and I even wipe those down with either Vaseline or Tuf-Glide before putting them away. I even store them with silica packs inside the factory baggy.

[Fireman]

I notice this effect on my knives. I live near the coast. Sometimes I can tell the loss of edge bite after a few days of resting on my dresser. A couple strop strokes and we are back to crispy clingy edges. I like my edges to be clingier than my high school girlfriend. I should do a test with the same knife edge half oiled and half dry.

[Sonorum]

I've had the same thought. If I've sharpened my GB2 to a good hair shaving level and then not edc'd it for two weeks I feel like it doesn't have the sam sharpness.

It doesn't feel like a stretch of the imagination that the thinnest part of a tool steel would be affected just by sitting.

[yablanowitz]

My K390 Police with pakkawood scales....

Blade swap, or did I miss something? My pakkawood P4 is HAP40.

[vivi]

blade swap.

[WilliamMunny]

Happy someone posted this as I thought I was going crazy. I experienced this with my S30V Manix 2. I know it is stainless but I would get a great edge on it, pocket carry it for a week or two barely using it. Then when I would need it it would not have the same bite. I also am in the DC area with high humidity.

[ChrisinHove]

My understanding is that corrosion will certainly degrade an edge.

Vivi’s remarks suggest that the degradation is a) slower than dulling through use, and b), some uses will inhibit corrosion.

None of which is really a surprise.

[wrdwrght]

Give most blade steels something to react to (in chemistry’s sense) and you’re likely to experience dulling unrelated to use.

Among Spyderco’s steel offerings, only H1 seems to be practically inert.

[TkoK83Spy]

I've noticed this with mine as well too. Nothing a couple licks on a stone or strop can't fix, still kind of strange though.

[Fireman]

I have not noticed this with LC200N

[aaronkb]

Happy someone posted this as I thought I was going crazy. I experienced this with my S30V Manix 2. I know it is stainless but I would get a great edge on it, pocket carry it for a week or two barely using it. Then when I would need it it would not have the same bite. I also am in the DC area with high humidity.

To be totally honest with you, based on my experience in DC I would never expect it to happen that fast with s30v. I’d be curious to know if it happens the same way if you sharpen and don’t use it at all for that same period of time in order to rule out the possibility that you have a burr left on there.

Burr removal has been by far my biggest challenge with sharpening - far too many times, I thought I’d removed it when I only straightened It out to align with the edge. This causes it to feel crazy sharp but the burr folds over after opening a few boxes and the knife edge is left rounded and dull.

Which will absolutely leave you thinking your crazy if you don’t know what’s going on. It’s the worst.

[K1500]

As mentioned Lance (surfingringo) has mentioned this and it jibes with my experience as well. To paraphrase Lance, he mentions that some ‘regular’ stainless blades will significantly dull without use just by being in/near a corrosive environment. Not so with LC and some of the other super stainless blades.