Let's take a look inside my Police 4

[vivi]

The weather is beginning to cool off so I thought I'd get my Police 4 ready to go back into rotation.

I stopped carrying it months ago because I noticed the liners corroding.

Here's what it looks like prior to being cleaned up:

























The knife was carried fall 2018 to spring 2019.

I'm glad a stainless Police 4 is right around the corner.

[TkoK83Spy]

Wow, definitely expect that much corrosion considering you're not in the most humid of environment, especially that time of year.

[captnvegtble]

I don't understand why the liners would be corroded... they aren't K390. Usually even on a non-stainless steel blade the liners are still stainless.

[JonLeBlanc]

Yep I've got a little bit (not too much) of the same thing going on in the handle of my P4, and I live in a VERY humid environment. I don't plan on taking it apart until and unless it gets to be as bad as yours though. Surprisingly, my blade is still clear and bright! Vivi can you post some pics of yours after cleaning?

[ladybug93]

this is exactly why i don’t understand everyone’s obsession with rusty tool steels. i’m surprised the liners are more rusted than the blade, but maybe it makes sense since you’re using the blade and the liners don’t get wiped down. anyway, when we have lc200n, h1, and others, i don’t understand why they’re not being used more. i know everyone has different preferences, but i would personally feel really ill if i paid this much for a knife and it looked like this.

[JonLeBlanc]

this is exactly why i don’t understand everyone’s obsession with rusty tool steels. i’m surprised the liners are more rusted than the blade, but maybe it makes sense since you’re using the blade and the liners don’t get wiped down. anyway, when we have lc200n, h1, and others, i don’t understand why they’re not being used more. i know everyone has different preferences, but i would personally feel really ill if i paid this much for a knife and it looked like this.

Well, as you say people have different preferences, and some of us just enjoy sharpening and the response one gets from tool steels and carbon steels can be very satisfying And of course, they can be cleaned...

[ferider]

I don't understand why the liners would be corroded... they aren't K390.

You dont know that.

[JuPaul]

I don't understand why the liners would be corroded... they aren't K390.

You dont know that.

Spyderco's description of the police 4 in k390 says stainless steel liners.

[captnvegtble]

I don't understand why the liners would be corroded... they aren't K390.

You dont know that.

Spyderco's description of the police 4 in k390 says stainless steel liners.

Correct. So not only does Spyderco tell us they're stainless steel liners, but we also know that K390 is a more expensive steel upgrade... so a business wouldn't intentionally use a more expensive corrosion prone steel for handle construction without any benefit.

[curlyhairedboy]

I think the condensation and evaporation of sweat is a knockout punch on a bunch of stainless steels. You get salt, water, and a bunch of oxygen, cycled over and over and over...

[JonLeBlanc]

I think the condensation and evaporation of sweat is a knockout punch on a bunch of stainless steels. You get salt, water, and a bunch of oxygen, cycled over and over and over...

Yep, that combo definitely will corrode a number of steels.

[vivi]

I think the condensation and evaporation of sweat is a knockout punch on a bunch of stainless steels. You get salt, water, and a bunch of oxygen, cycled over and over and over...

Yep, that combo definitely will corrode a number of steels.

I wonder if it was the blade causing a reaction or if the liners are made of a different material. I've carried a Police 3 year round for years with much less corrosion on the liners, and none IIRC on the back spacer, blade and lock bar.

[silvershade255]

Hmmmm......with the police 4 lw coming out I wonder what would happen if you switched the blades (assuming the can be)

And if it is a result of a galvanic reaction what if the washers were replaced with nylatron?

[James Y]

If you have an Endura 4, have the liners rusted in the same manner? I don’t disassemble my knives, but from a cursory check with a flashlight, I haven’t been able to detect any visible rust on my knives’ liners. The new VG-10 Police 4 LW will likely react the same way that an Endura 4 would.

Also, keep in mind that some people’s perspiration is more acidic or corrosive than others’.

Jim

[vivi]

If you have an Endura 4, have the liners rusted in the same manner? I don’t disassemble my knives, but from a cursory check with a flashlight, I haven’t been able to detect any visible rust on my knives’ liners. The new VG-10 Police 4 LW will likely react the same way that an Endura 4 would.

Also, keep in mind that some people’s perspiration is more acidic or corrosive than others’.

Jim

I rusted the liners on my Police 3 in VG10, but that took me 3-4 years of year round carry, and the rust was about 30% of what happened with the Police 4. Don't recall any rust on the blade, backspacer or lock bar on the P3.

I knew the blade on the P4 would require more attention, but I did not expect the same of the liners.

[JonLeBlanc]

Also, I'd like to point out that we don't know exactly *what* the liners are on the P4. Ok, so they're stainless steel...

[Cambertree]

Good stuff, Vivi - I'm glad to see your P4 is going back into your carry rotation.

I've had a similar experience with the liners on my Police 4.

I think Curlyhairedboy has hit the nail on the head:

I think the condensation and evaporation of sweat is a knockout punch on a bunch of stainless steels. You get salt, water, and a bunch of oxygen, cycled over and over and over...

The liners are definitely stainless, not K390 or some type of simple carbon steel.

This is easily confirmed by looking at the polished spine area of the handle, where the backspring, backspacer and the edges of the liners are. On mine there's not a hint of patina or corrosion there, despite constantly being in contact with sweat, vegetable fluids, damp environments etc when being used. Even the most highly polished carbon steels show patina and pepper spotting after some use. If you drop some lemon juice on there, there'll be no reaction.

We also see the question come up from time to time, about whether the liners of a knife are the same material as the blade. Except for the LC200N knives, I don't believe this is ever the case. The properties required for liners are completely different to what are required for a high performance blade.

In general for liners, you don't need high wear resistance, high hardness, or the high carbon content of most bladesteels. Steels like the 420 series in that sense are superior materials for liners than, say CPMS30V or K390.

316 austenitic stainless would be extremely corrosion resistant, but as Sal has referenced hardening and even cryoing their liner material before, I would conjecture that most liners are probably a martensitic 420 stainless, possibly 440 in some cases.

Assuming that everything was done right with the steel grade and heat treatment itself, the issue seems to me that the liners are not highly polished on the inside. I think the machining striations and slight unevenness in the surface on a microscopic level, may interfere with the integrity of the passive chromium oxide layer.

There may also be a slight influence from galvanic corrosion, but on mine I didn't really see that there was a greater amount of rust around the pivot action, where you would expect to have the most contact between the K390 blade and the liner material. There was a fair bit of patina on the liner scales there, but I would expect that.

Also, the skeletonising of the liners probably allows salty/acidic moisture to collect at the edge of the liner holes and gradually wick into the tightly fitted gaps between liners, backspring, scales etc.

It would be interesting to check, but I think the other G10 Seki knives are probably highly polished on the inside surfaces. I don't recall seeing more than a tiny bit of oxidisation on the insides of a G10 Dragonfly I gifted a friend which has had constant daily use for years now.

I should note as well, that my knife was bought second hand, and the first owner carried it in the tropical Northern Territory of Australia. I then used it for over a year constantly, often in the kitchen, and with wet or damp hands before opening it up to have a look.

A couple of previous discussions and pics on the subject:

viewtopic.php?f=2&t=84180&p=1339419&hil ... 4#p1339419

viewtopic.php?f=6&t=58681&p=1338033&hil ... d#p1338033

[The Mastiff]

Nah!, There is no rust there. It's in everyone's imagination.

Actually I am pretty curious why the liner is rusting worse than the blade steel in areas of the blade that are difficult to get to and don't see whatever maintenance Vivi is putting his non stainless blades through even if it's just wiping it down on his pants when wet. Those liners should be pretty corrosion resistant compared to the K390 I would think.

My mind strays to some sort of current/galvanic action or the way the liner material is heat treated but I wouldn't bet money on either. If it has a rough surface finish that gives a quicker corrosion but I wouldn't bet on that either. It's not the first we have seen and Vivi isn't the only one it has happened to.

We do know that if it is possible Vivi's knives will be a sure bet to show corrosion even when it's not supposed to be possible. I'd be trying quick actions to slow the corrosion by doing stuff like giving the knife a quick rinse with clean bottled water ( distilled drinking water preferably) after carrying the knife on sweaty days or after a ride. Pour water in/on it, shake it off and put it on the bedside table ( or wherever ) to dry. Just leaving the knife coated in sweat to dry with the salt still on it will find plenty of moisture from the air ( Average dew temp of 72-73 degrees overnight this time of year here means lots of humidity available) I also keep the insides wiped down with a dry silicone cloth as best as I can and that helps a bit but what Vivi's knives have to deal with is worse than what my knives have to endure by a long shot now that I'm retired and not working the yard on concrete and asphalt like I used to do daily all summer long.

[Pancake]

That is some nasty rust!

My Police 4 will hopefuly show up next week, so maybe I take some it apart right away and polish the liners a bit with some 500 and 1000 grit sandpaper.
Maybe a even a light coat of some oil or way would help......I made some coconut-beeswax paste for wood so maybe I try that (dont have any fancy waxes or a special paste).

EDIT: Only thing that I rusted so far in my Spydercos is stop pin in PM2. LIners were ok, blade ok, only the stop pin has rust on it. But after sanding and polishing it was much better, I get some color changes but not a reall rust.

[Cambertree]

My Police 4 will hopefuly show up next week, so maybe I take some it apart right away and polish the liners a bit with some 500 and 1000 grit sandpaper.
Maybe a even a light coat of some oil or way would help......I made some coconut-beeswax paste for wood so maybe I try that (dont have any fancy waxes or a special paste).

It probably wouldn't hurt to do that. Just be careful not to round over the squared off edges of the liners, or you won't have that nice flush fitting look on the spine.

I was quite surprised when I took mine apart, as I had been wiping down the inside with mineral oil after use and drying it on top of a heater. After sanding mine a bit, as shown in one of the linked posts above, I used Tuf-glide and let it dry before putting it back together.

Wax isn't a bad idea, I'll try Ren wax the next time I take it apart, depending on how effective the Tuf-glide and smoother surface finish has been.

Here's a couple of questions for the metallurgy and science buffs, and please excuse my ignorance:

Does galvanic corrosion always require both metals to be in physical contact with each other?

Is there any mechanism by which a steel can be more susceptible to corrosion by simply having another metal in very close proximity to it?