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coatings for corrosion resistance

Posted by sal 
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sal
coatings for corrosion resistance
June 18, 2018 02:25PM
The subject of coatings for protection against corrosion in non stainless steels is always a question. I recently posted this on the Spyderco site forum when asked.

There is still argument over whether or not coatings help with corrosion resistance. Some feel that it does protect the non stainless blade and others feel that moisture seeps in and causes corrosion underneath the coating (which one cannot see) and it is not obvious unti the corrosion gets so bad it breaks through the coating and then the blade is pitted too much to clean.

Probably a good subject for discussion here as well?

Maybe we can sic Larrin on this also?

sal
Re: coatings for corrosion resistance
June 18, 2018 02:55PM
Well as these good quality coatings require 200-500C temperature it limits
to use it on the steels with high temper cycles so possibility of having
a steel with good pitting resistance is not known to me.
Maybe RWL-34/CPM-154 at low 200C temper but I am not sure
about the coating quality. And as it polishes very well it isnt really
steel one would want to coat either for corrosion or aesthetic reason.

Maybe some more simple carbon steels for cutting materials
and in evviroments not containing much of the hard particles.
And when sharpening them ensure to sharpen the whole bevel
up to where coating starts, not just the very apex.
For obvious reason of some corrosion remaining where
the coating begins at sharpened bevel.

I used some blades with DLC done at 200C and its quite durable..
Drawback also is when You sharpened it a lot and it needs regrind
the primary geometry - may spend one extra belt.

Most coatings lowers friction and prevent stickage quite well while
yet in a good condition.

And remember they are basically ceramics !
So can use the knife bevel as a hone.

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Re: coatings for corrosion resistance
June 18, 2018 09:09PM
I haven't ever had a problem with coated blades corroding, except on the edge bevel that isn't coated, that rusts if I don't either keep it dry or oiled.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: coatings for corrosion resistance
June 18, 2018 10:05PM
I cannot possibly begin to guess at whether or not coatings to prevent corrosion from passing through or not, I would think so, at least in, say, cookware, how commonly do you see rusting on a teflon/ceramic coated pan, left under water and grease for hours? I know the point is that you wouldn't, and sure, pans don't see the same kind of shock as knife blades, nor are typically as thin, but I am curious what that industry says about them.

However, Jason made a fairly good point up there, when it comes to using coatings with non-stainless steels, which is the need to keep the edge clean and possibly even oiled to prevent corrosion there. One point then would be: is the failure seen in coated knives happening due to corrosion behind the coating, somehow, or did the damage start with corrosion at the un-coated edge, which traveled up from there. And then another point is, if you need to be careful about cleaning and oiling the edge, what's stopping you from doing so with the rest of the blade?
Re: coatings for corrosion resistance
June 18, 2018 11:33PM
Quote
Luisknivacc
And then another point is, if you need to be careful about cleaning and oiling the edge, what's stopping you from doing so with the rest of the blade?

Exactly, it is an improvement but doesnt mean no maintenance at all..

In knives like any other part if you will f.e. dig in rocky soil and use your blade
outside or wet corrosion will start in scratches and slowly eat underneath.
So in such conditions and use one should simply start oiling the whole
blade in the same way as it would not be coated.

Not particularly on knives but seen many parts to have corrosion under chrome or zinc layer.
After years of use in dirt and outside like cars and car parts f.e.

Luis, cookware is either from cheap aluminum alloy
(like suspiciously lightweight pancake pans - bottom always warps over time

cast iron (rarely these days but favorite of many pro cooks),

most not crap cookware is from austenintic stainless.

Possibly some cheap cookweare can be from ferritic stainless
that is less stainless as the austenitic one.

Coating on the pans is there totally to prevent sticking food..

F.e. 420 cant even compare to something like 304 in corrosion
resistance and many cheap knives from 420 that has been never
intentionally oiled, washed by detergents and left wet on daily basis..
still have no rust after decades..

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Edited 2 time(s). Last edit at 06/18/2018 11:43PM by JSCT.
Re: coatings for corrosion resistance
June 19, 2018 04:57AM
Do not have experience with coated non stainless steel blades, but I remember a YouTube video about mid 70's Gerber M 2 or M 4 steel hard chrome plated knife with sevier pitting under the plating.

I look at coated blades more in the line of visual effects to the consumer than substitute to basic maintenance...

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Re: coatings for corrosion resistance
June 19, 2018 08:46PM
A natural patina (native oxide passivation) has never been problematic, although it is not very cosmetic.
Re: coatings for corrosion resistance
June 19, 2018 11:32PM
Quote
RFL
A natural patina (native oxide passivation) has never been problematic, although it is not very cosmetic.

I have san-mai gyuto w aogami super core that forms bautiful purple-blueish patina after red meat..
But I never liked dark etched blades neither..

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Re: coatings for corrosion resistance
August 10, 2018 12:14PM
I have not discussed coatinrgs on non stainless with our desalination plant metallurgist at work but:

According to this article there is an improvement in corrosion resistance in the use of DLC in desalination plant when applied to 316 stainless:

[www.sciencedirect.com]

I will ask around the plant metallurgist here on the mine a bit.
sal
Re: coatings for corrosion resistance
August 10, 2018 04:03PM
Thanx Marthinus,

316 is usually not a problem. Blade steels with their higher Carbon content is the problem.

sal
Re: coatings for corrosion resistance
August 10, 2018 10:51PM
I'll offer up a point of few that really doesn't answer Sal's question, but myself I see no point in blade coatings. My only area of corrosion concern has always been the apex.
I do notice loss of fine cutting edges due to corrosion, which irritates me. But my flats I really don't care about.
Re: coatings for corrosion resistance
August 11, 2018 03:03AM
I've always liked DLC on stainless. Really durable, can have a nice aesthetic appeal if the steel is high polished.

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Folding knives are fun, fixed blades are important.
Re: coatings for corrosion resistance
August 11, 2018 10:29PM
Quote
sal
Thanx Marthinus,

316 is usually not a problem. Blade steels with their higher Carbon content is the problem.

sal

DLC surface will increase the corrosion resistance of them too..
Actually if it could increase corrosion resistance on an alloy
that is already very resistant like 316 it means on higher carbon
steels it will have even more possitive effects..

Perhaps the apex of the edge will always corrode quicker than flats
as its 1um thick surrounded by enviromental infulences from 330deg
compared to flats surrounded from 180deg only..

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Re: coatings for corrosion resistance
August 25, 2018 09:20AM
Quote
JSCT
Quote
sal
Thanx Marthinus,

316 is usually not a problem. Blade steels with their higher Carbon content is the problem.

sal

DLC surface will increase the corrosion resistance of them too..
Actually if it could increase corrosion resistance on an alloy
that is already very resistant like 316 it means on higher carbon
steels it will have even more possitive effects..

Perhaps the apex of the edge will always corrode quicker than flats
as its 1um thick surrounded by enviromental infulences from 330deg
compared to flats surrounded from 180deg only..

Some feedback.

Metallurgist indicated they use multilayer and single layer DLC in the plant and on our mine’s pumps. Multilayer for parts that have potential to get knocked around to prevent fatigue cracks and single layer for simpler less demanding jobs.

Aditionally what they have found is that the method of application, apparantly there are a few methods of application, effects the corrosion resistance of the DLC.

Sal.

To give you an idea of the past mining issues we are trying to resolve, a full 316 pump lasts less than 40 hours. We are dealing with water in pH range of 2.3-2.5 woth heavy metals and sulphate within the water. Some nasty acid mine drainage. Full HDPE pumps have been developed as no method of coating has proven to keep a pump operational for mpre than 4 months. Before the HDPE pumps modified 316, heavily chrome plated and DLC coated pumps among other trial pumps were aparrently used.

Metallurgist also indicated that DLC R and D work is done woth specialists to resolve project specific issues for the mining industry.
Re: coatings for corrosion resistance
August 27, 2018 02:24AM
Well, sure but several months in contact with acid solutions of ph under 2,5
is pretty overkill for any knife application for a hand knife I can imagine..
So I only had a certain application in mind..

Unless there is a coating that can be applied to the cutting edge just as the rest of the blade
without negatively impacting high level of sharpness I think there is no point functional point
to use it.. and even then it would be just until the last sharpening..

If the edge rusted away while blade is nicely coated fuction is lost the same
as it would be all stained.. actually this removes the possibilty of indication
the its time to care of the blade as one can see no patina forming progress
nothing.. f.e. my friend mirror polishes K390 blades and sharpen edge
on 6000 natural stone on tormek perhaps he use simple carbon damascus
for guards on these knives so they rust always sooner than your edge or blade..

www.instagram.com/jscuttingtools
Re: coatings for corrosion resistance
August 27, 2018 02:31AM
A gunsmith channel on youtube has harped on the point that the end use ulitmately has to do the maintence if they want to expect their product to last.

Yes, a corrosion resistant coating is nice, but the end user has to take care of their own stuff.

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Bill22252 on YouTube. "See you space cowboy"

Resident Emerson Fanboi

Folding knives are fun, fixed blades are important.
Re: coatings for corrosion resistance
August 27, 2018 05:41AM
JSCT,
Awesome point.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: coatings for corrosion resistance
August 28, 2018 04:11PM
Juraj Trnka K390

Best coating is mirror cool smiley

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