what the... rusty blade coatings? explain please?

[SPNKr]

The first picture doesn't look like rust, you could probably wipe it off. As for the coatings, it is possible they are inducing rust. Some coatings are placed on non-stainless blades to protect them from humidity, yes, but if such a coating is placed on a stainless blade it is reasonable to assume corrosion resistance was not in mind. As the coating appears matte to the eye it's easy to understand the surface structure is not smooth. It consists of microscopic peaks and valleys which could have trapped corrosive substances such as your lemon juice for extended periods of time despite you wiping it down, essentially soaking the steel in it as previous posters have correctly pointed out the coatings may not completely seal the blade.

My only advice to you would be not to treat the coatings as any form of corrosion resistance unless it is explicitly said to, or has been extensively tested to be and wash it thoroughly after it comes into contact with corrosive substances. If eventually you find that it still rusts more easily and are not crazy over the aesthetics, you may find it beneficial to strip the coating off completely.

To the above posters claiming the structure of steel to be monocrystalline and claiming carbon to be a catalyst for the oxidation of iron into iron (III) oxide, i.e. rust - I mean no offense but please do a little bit more reading and research before attempting to post so authoritatively on a topic. I have yet to come across literature even briefly mentioning the latter and the former is just simply false.

 

[fzla226]

The carbon in diamond and other stuff is pure carbon in a mono-crystalline structure, the carbon in steel is a single atom in a molecule and is very receptive to bind with O2 to forum rust (its the O2 in water that causes rust, not the water [or the hydrogen])
What's been said is true, it is the carbon in the steel that rusts, that's why spyderco's H1 and N680 is infact rust proof, because those steels contain zero carbon, as mentioned other than the few true rust proof steels all carbon containing "stainless" will eventually rust.

N680 and H1 have carbon in them. H1 a small amount and N680 is something like .5% carbon.

 

[Freman Bloodglaive]

To the above posters claiming the structure of steel to be monocrystalline and claiming carbon to be a catalyst for the oxidation of iron into iron (III) oxide, i.e. rust - I mean no offense but please do a little bit more reading and research before attempting to post so authoritatively on a topic. I have yet to come across literature even briefly mentioning the latter and the former is just simply false.

He said that diamonds were mono-crystalline, not steel.

Carbon taking the chromium out of solution in the form of carbides makes sense, hence ZDP-189 which has 20% chromium, but ends up with very little free chromium because the 3% carbon sucks it up. A very hard (potentially) steel, but also very rust prone.

 

[RevDevil]

N680 and H1 have carbon in them. H1 a small amount and N680 is something like .5% carbon.

The carbon left over is so miniscule amount it can be categorized as an impurity more so than an alloying material. Certainly not enough to rust. I think Sal Glesser or someone else stated the leftover Carbon in H1 was about .015%, not .5% (which is a much greater amount).

 

[goodeyesniper]

So you carry some cloth with you at all times and use it every time you use your knife.
Out of curiosity; why not get a stainless knife instead?

I'm not a nudist, so yes, I always have cloth to wipe it off on. besides, where would I clip it if I was always nude? (aka, I wipe it off on my jeans/shirt, not too complex of an issue) and it's not always ah instant thing. my opinel can often be found open and dirty on my work stand, out near the dumpster, or anywhere else near where I am currently working. just, before I move on and switch tasks, I generally swipe it on my jeans real quick then pocket it... same thing I would do with a stainless knife, a flat head screwdriver, a cell phone, etc...

and I actually do carry stainless some of the time. guess what, it takes an identical amount of upkeep to keep them clean as carbon. cleaning solidified gunk or tape residue off of carbon takes just as much time on stainless. I have found cleaning off a light speckling of rust takes less effort than cleaning off old tape residue.

and about my whole "mindset" bit. clearly changing how I think about it doesn't actually remove rust. it's just sort of the same thing as leaving your house with a smile, and your whole day being better. does starting the day off in a good mood affect everything else? not really. but it affects how you react to everything else.

or think of a skilled mountain biker who finds a new trail that repeatedly kicks his butt. then one day, he sort of switches everything off and hits all the right lines and cycles the path with ease.

on paper, preventing rust is far more simpler than that, yet knife enthusiasts continuously have issues with it. it really is as simple as a two part problem:

is the blade in contact with a corrosion causing medium?
if so, for how long?

period. it's not about oils or coatings or special wipes. it's about not leaving it exposed to a corrosive for any length of time. different uses and environments call for different methods. and oils, coatings, or special wipes might be just what you need, but if you skip the simplified understanding of why it forms and jump straight into internet recommendations about how to keep it away, chances are you'll get rust under your coating of choice eventually, and then freak out online

 

[Bigfattyt]

show me from the manufacturer website or other sources these words. ive never heard this before in 12 years of collecting, and sharpening and researching knives that a coating is not applied with *only* light/glare reduction and *no benifit* to corrosion resistance. especially when the exposed and bare metal is still polished. my tungsten wedding band is not corroded and yet the tungsten DLC is. why is this seemingly normal to everyone

Tungsten is not steel. It's tungsten. Your ring is not a thin tungsten coating over a steel core. Your tungsten ring won't rust.

I had a CRKT M14 that was a rust bucket. It had a slightly rough bead blasted finish, that was an absolute beast for rust. My bare polished carbon steel, or patined carbon steels were 100 times better at not rusting.

 

[JParanee]

Tungsten is not steel. It's tungsten. Your ring is not a thin tungsten coating over a steel core. Your tungsten ring won't rust.

I had a CRKT M14 that was a rust bucket. It had a slightly rough bead blasted finish, that was an absolute beast for rust. My bare polished carbon steel, or patined carbon steels were 100 times better at not rusting.

I agree

The more aggressive the media used to blast steel the more it attracts rust

The tactisissie craze has forgotten how well a mirror polished carbon steel blade will resist rust

I have humped carbon steel blades on 4 continents from jungle to extreme elevation and thru proper Maintence kept carbon steel blades with out rust

In all military history show me a case of the glint of a blade giving someone away by accident

Quite the opposite ...... A polished blade has been used as a signal mirror by stranded outdoorsman and military personal more than once

These guys that need coated stainless blades jeez

 

[fzla226]

The carbon left over is so miniscule amount it can be categorized as an impurity more so than an alloying material. Certainly not enough to rust. I think Sal Glesser or someone else stated the leftover Carbon in H1 was about .015%, not .5% (which is a much greater amount).

Uh I didn't say H1 had .5%. That was referencing N680.

 

[Ebbtide]

Blade coatings are a way for manufacturers to skip on the final finishing.
A good mirror finish is way more labor intensive than a coating.
Once the blackticle craze took off, manufacturers were thrilled... more volume, less expenditure.

I stripped off the coating on my CS RS and it looked like a piece of bar stock underneath.
No shiny, pretty blade under that black epoxy coat.

As for the rust... humidity can be sneaky.
Air conditioned house.
Knife sits on table overnight and get chilled to room temp.
Knife goes in warm pocket, out into the hot humid air.
Just like a can of cold beer going from the fridge to the back yard... to a lesser degree of course.

 

[fzla226]

Blade coatings are a way for manufacturers to skip on the final finishing.
A good mirror finish is way more labor intensive than a coating.
Once the blackticle craze took off, manufacturers were thrilled... more volume, less expenditure.

I stripped off the coating on my CS RS and it looked like a piece of bar stock underneath.
No shiny, pretty blade under that black epoxy coat.

As for the rust... humidity can be sneaky.
Air conditioned house.
Knife sits on table overnight and get chilled to room temp.
Knife goes in warm pocket, out into the hot humid air.
Just like a can of cold beer going from the fridge to the back yard... to a lesser degree of course.

Uh. You do know that you have to finish a blade to have a coating properly set right? It's called bead blasting.

 

[plue]

Is this a joke? Because it is certainly nonsense...



TO the OP, I see a lot of gunk in the first image that is orange like rust and seems to be washing out from the pivot area or the thumbstud of the CRKT - perhaps you have some non-stainless metals there?

In the second image, rust. Is it stainless steel or just polished tool steel? Probably the latter. If it becomes a problem, definitely treat it as indicated by others above.

In the third image, I see some orange within the serrations where bare metal meets coating - is that what you are talking about? The scratch pattern in the bare serrations could easily collect moisture form the air, the interface where the coating begins is a good condensation point so there could be such minor oxidation occurring there, or it could just be collected material from elsewhere that is sticking at the interface. IF corrosion is occurring there, a simple polish of the area (reduce the scratch pattern) may suffice to prevent recurrence. There is sufficient free-chromium in the matrix of these steels to keep corrosion to a minimum, but as already stated it does not eliminate it.

No where do I see the coating causing or enhancing corrosion, no "rusty blade coatings".

First response to this thread that made sense.

Uh. You do know that you have to finish a blade to have a coating properly set right? It's called bead blasting.

While I do not know much about the process of application of coating to a blade, from what I've seen of people stripping coated blades (Becker, Busse, etc.) none of them were bead blasted.

 

[Czechmate]

After reading this entire thread I've determined there is only one solution; to soley buy rosta-frei knives!

I've started collecting 'em already.

 

[Shotgun]

Uh. You do know that you have to finish a blade to have a coating properly set right? It's called bead blasting.

I've stripped several knives. Not a bead blasting in the bunch. They've all had rough grind marks. It is way cheaper to leave the knife at say a 200 grit belt and then coat it with paint then it is to polish that blade up past 2000 grit. I share the opinion that blade coatings are primarily for the tacticool crowd and for manufacturers who want less overhead.

 

[Czechmate]

I've stripped several knives. Not a bead blasting in the bunch. They've all had rough grind marks. It is way cheaper to leave the knife at say a 200 grit belt and then coat it with paint then it is to polish that blade up past 2000 grit. I share the opinion that blade coatings are primarily for the tacticool crowd and for manufacturers who want less overhead.

My experience has been a mixed bag as I've had some knives that looked amazing stripped (ie> more finish work prior to coating) or some that looked :thumbdn::thumbdn::thumbdn: and would need a LOT of sanding to get them looking decent.

I do agree with the last line 100% though.

 

[Ebbtide]

Uh. You do know that you have to finish a blade to have a coating properly set right? It's called bead blasting.

uh... I know what I saw and it wasn't bead blasted.

I've stripped several knives. Not a bead blasting in the bunch. They've all had rough grind marks. It is way cheaper to leave the knife at say a 200 grit belt and then coat it with paint then it is to polish that blade up past 2000 grit. I share the opinion that blade coatings are primarily for the tacticool crowd and for manufacturers who want less overhead.

That about sums it up.

 

[sebaldus]

The first picture doesn't look like rust, you could probably wipe it off. As for the coatings, it is possible they are inducing rust. Some coatings are placed on non-stainless blades to protect them from humidity, yes, but if such a coating is placed on a stainless blade it is reasonable to assume corrosion resistance was not in mind. As the coating appears matte to the eye it's easy to understand the surface structure is not smooth. It consists of microscopic peaks and valleys which could have trapped corrosive substances such as your lemon juice for extended periods of time despite you wiping it down, essentially soaking the steel in it as previous posters have correctly pointed out the coatings may not completely seal the blade.

My only advice to you would be not to treat the coatings as any form of corrosion resistance unless it is explicitly said to, or has been extensively tested to be and wash it thoroughly after it comes into contact with corrosive substances. If eventually you find that it still rusts more easily and are not crazy over the aesthetics, you may find it beneficial to strip the coating off completely.

To the above posters claiming the structure of steel to be monocrystalline and claiming carbon to be a catalyst for the oxidation of iron into iron (III) oxide, i.e. rust - I mean no offense but please do a little bit more reading and research before attempting to post so authoritatively on a topic. I have yet to come across literature even briefly mentioning the latter and the former is just simply false.

Well said SPNKr. I just want to add some things about corrosion to clear up any misconceptions. Stainless steels are resistant to corrosion due to the a phenomena called 'Passivation' in which a very thin layer of Chromium forms on the surface of the steel. This layer prevents further oxidation, i.e. rust, when exposed to water. The reason that so called 'carbon steels' rust is not due to the amount of carbon in the steel but is due to the simple fact that it has less chromium content. In fact, some stainless steels have just as much carbon as 'carbon steels'.

Staying on topic. I don't know which coatings are on your knives but I'll assume DLC coatings. DLC coatings are known for their hardness, wear resistance, and low coefficient of friction-- not chemical resistance. Plus, like SPNKr said, the matte finish implies a rough surface that probably has a large porosity which can trap nasty citric acids. Keep in mind that the iron in your knife would much rather form rust (more energetically favorable) than stay bonded to the amorphous carbon coating-- so don't give it a chance! Also I am not 100% sure on the amount of surface chemistry necessary to adequately bond DLC coatings to the surface on stainless steels but maybe the passive layer is removed when the DLC is deposited and ruins the corrosion resistance under the coating.


TL;DR: clean your blades if you expose them to lemon juice.