How Rust Resistant Is A M4 Knife Blade If It Has A DLC Coating?

DLC/PVD Misinformation

No, it's not a particularly pervasive thing, but after seeing someone actually parrot Skelton's ignorant nonsense about DLC coatings (and after reading advice from someone wiser than myself) I figured why not start this thread. While my background in material science is limited (but not...
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kobold said:
DLC is porous, so it can actually trap moisture which will promote rust. I think it is best to saturate the pores with a drying oil.
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Woah - never thought to use Tung oil on metal - does it do better than mineral oil? I imagine it sticks better… (just realized you were talking about using it over the DLC coating, but I’m still wondering how drying oils would do on carbon steel…)
 
scdub said:
Woah - never thought to use Tung oil on metal - does it do better than mineral oil? I imagine it sticks better… (just realized you were talking about using it over the DLC coating, but I’m still wondering how drying oils would do on carbon steel…)
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With mineral oil we can just reapply it like we would do with a carbon steel. As for drying oils, BLO (boiled linseed oil) will work just fine. I think it is called polymerization, the result is kinda like linoleum. Probably multiple coating are needed, but it will be well sealed for years..
 
kobold said:
With mineral oil we can just reapply it like we would do with a carbon steel. As for drying oils, BLO (boiled linseed oil) will work just fine. I think it is called polymerization, the result is kinda like linoleum. Probably multiple coating are needed, but it will be well sealed for years..
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Is linseed poisonous? And would there be a food safe option if it was.
 
Drop bear said:
Is linseed poisonous? And would there be a food safe option if it was.
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Linseed (flax) is not poisonous, but BLO is. Although I would bet that according to the MSDS it will be safe enough in this application.
BLO doesnt really mean it was boiled, but they added accelerants to it. Regular linseed oil can be used, but the drying times will be long (weeks), so applying multiple coatings might take months. It is perfectly doable though and it would be food safe.
 
GatorFlash1 said:
Is a CPM M4 blade steel with a black DLC coated blade on a knife rust resistant?
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My M4s are amazing cutters, but M4 rusts or stains if I look at it funny. I have a DLC coated one, I would expect the edge to rust quick. I would put food grade oil (go to the kitchen or wipe some fries on it!) or edible wax on the blade of any M4 knife.
 
Google images of DLC coating and rust. You can see images of DLC coated M4 that has developed rust. As previously said, DLC is porous and rust can form under it and migrate. It does hold oil well, so keep it oiled if rust is a concern.
 
Sonnydaze said:
My Gayle Bradley 2 (Spyderco) doesn't seem to need a coating. Just clean and dry the blade when you're done with it.
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This. My GB2 is one of my most used knives (since it’s in my workshop), no maintenance besides sharpening, no rust.

M4, 4V, and A2 do pretty well for me, DLC or not.
 
Are you trying to use DLC to protect the aesthetics? or the durability and performance of your knife.

In terms of performance and durability, before the rust deals any real damage to your blade stock, it would have already wrecked the edge.
 
I was wondering about this too, I bought my girlfriend a DLC coated M4 Sage for Valentines day, going to dye the scales purple and slathered the blade in mineral oil, what else to do?
 
I think a lot of the rust hinges on your environment and personal chemistry.

I have a bunch of M4 uncoated blades and the only time they'll get some rust is if I force a patina. There will be a couple orange spots in the jimping or around the pivot but that's about all. And I don't need to pack them away in oil either.
 
My understanding is that the DLC is porous and not a rustproofing by itself , but can help hold onto oil or other rust barriers you apply . :cool:
 
One of the questions you may want to ask yourself is how well your other knives stand up to rust. I know guys who can't carry a gun or knife without constant maintenance due to the acidic nature of their own perspiration. Meanwhile, there are plenty of guys who can carry the same weapons and blades, and never ever have a hint of an issue.

Much like the above, there are storage locations which are concerns. If you find rust forming on your knives in a storage drawer or on your nightstand, you probably live in a high humidity area, near salt water, or something similar. People in other areas would think you are crazy as they never experience any issues.

In addition to the above, we can't look at DLC as one all encompassing treatment. It would be like considering all blade steels to be the same, and we all know that quite clearly they are not. In the world of DLC (Diamond Like Coating), we have to ask not only about the more obvious issues such as surface prep, but are we talking about Physical Vapor Deposition (PVD) or Plasma Assisted Chemical Vapor Deposition (PACVD)? Add onto this, there are 7 or 8 categories which exist in various forms... are we speaking about a-C (hydrogen-free amorphous carbon) or ta-C (tetrahedrally bound hydrogen-free amorphous carbon)? Or one of the others?

We can also now include that the DLC coating can be enhanced for corrosion resistance with the aid of "doping". Some examples would be doping with the additions of Si, F, Cr and Ti. We can also see a corrosion resistance increase by way of thickening the coating (we are talking super thin after all). We don't increase the thickness all at once as we are looking at creating possible metal weakening, so multiple applications are done instead.

Does a knife maker delve into all of these things? Or, does a company check off the block for DLC knowing its a good overall treatment and go with the lowest cost option? I think there are a lot of variables that we can look at, which allows us to tackle the issue in our own minds with the simple fact that we aren't going to know or find out short of some form of sending a blade out for testing to a laboratory. I personally don't think we are getting the best of the available options in DLC, but I do think most companies are getting us a finished product which is an actual improvement with using a DLC finish.

The issue as I see it, is that since not all DLC is equal, there is no hard answer to determine what we are getting to answer the OP.
 
I am able to carry straight carbon blades like Douk-Douk, Higo, K55 around without issue as long as I keep trusty mineral oil. Have not carried my Cruwear, REX45, or my girl's M4 yet (I think I want one for myself, I love the Taiwanese FRN comp lock leaf blade...)

So basically, if you can carry regular carbon steel a-ok with maintenence, will this M4 be any different? And if anyone knows, can you give me a rundown on Cruwear and REX45? I was of the opinion I must worry about the REX way more than the Cruwear. I live in SoCal. My REX45 will have DLC (and weigh half as much as my Espada XL with copper scales by Spyderco, ha ha!)
 
Hashishiin said:
I am able to carry straight carbon blades like Douk-Douk, Higo, K55 around without issue as long as I keep trusty mineral oil. Have not carried my Cruwear, REX45, or my girl's M4 yet (I think I want one for myself, I love the Taiwanese FRN comp lock leaf blade...)

So basically, if you can carry regular carbon steel a-ok with maintenence, will this M4 be any different? And if anyone knows, can you give me a rundown on Cruwear and REX45? I was of the opinion I must worry about the REX way more than the Cruwear. I live in SoCal. My REX45 will have DLC (and weigh half as much as my Espada XL with copper scales by Spyderco, ha ha!)
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I use a Rex45 Native Chief in the kitchen, no protection other than occasional fats from the food it cuts and no problems at all. It patinas a little bit, but nothing to write home about.

I have a less used cruwear fixed blade, always in its sheath, no signs of anything.

My GB2 in M4 underwent a hard use period when it did all my cutting for a month and failed to develop any rust. It was harvest and canning season, so lots of foodstuff, lots of acids, yet no problems.

CIMG0798.jpg
 
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