Rust questions

[Hair]

I know there is no hard and fast rules about rust as all steel and conditions are different, but I would like to learn a little more about rust in general.

These questions are mainly sparked by the rust that has appeared on my Mcusta between the start of my shift at work, and getting home (9 hours or so). The thread is here: http://www.bladeforums.com/forums/showthread.php?t=379192

I was surprised that the rust appeared so fast, and on an, as far as I could tell, dry knife. Now I am worried about rust.

1) I try to wipe off my knives with my shirt whenever they are handled, just to get any hand moisture off. I don't have any metal protectant yet, but I plan on getting some. If I use metal protectant on my knives, wipe them off after use, and try to keep an eye on them for rust (so I can remove it before it gets too excessive), will I have a pretty good game plan against it? Should I do more? Am I being excessive? How much should I worry about rust?

2) With stainless steels, is it fairly safe to use the knife in normal conditions (including somewhat sweaty hands) and not worry about wiping it off after use? I know stainless steel can rust, but is it very rare, or should I still wipe down my stainless steel knives after I have handled them?

3) With carbon and stainless steels, how much do you need to worry about rust? Of course they rust easier, but is it so extreme that you must dry the knife immediatly after getting wet? Can I use them without wiping them down? Or is drying them (of normal hand moisture) after each use very important?

4) If a knife gets some rust spots, and the spots are removed with a metal polish or rust remover like MiliTec, are there any long term affects? Or will the knife be as good as new? If someone didn't take care of their knife and had to keep removing the rust over and over, would the knife eventually "die"?

5) How much rust is bad for the knife? Are rust spots mainly cosmetic? At what point does rust become a matter of the knife's health and function and not just looks?

Personal cases:

-My Mcusta has some spots of rust on the scales. Do I need to worry about these right now (i.e. get some Militect tomorrow and remove them ASAP) or can I leave them for now and get some Militec when I get a chance? Will the rust spread? After I remove the rust, will the knife be as good as new?

-I have a Hen and Rooster stilleto that has some rust on the liners. It isn't on the "face" of the liners (where the blade goes when shut), but rather on the sides. So you can only see it when the knife is open and the liner moves into the locked position. Will this rust eventually compromise the liner lock and should be removed ASAP? Or is it mainly cosmetic and not a worry if I don't care about it?

I have a slipjoint that was in the garage for decades and got some rust on the blade and inside the liners. I asked about how to remove the rust and a couple people suggested that if the knife opens and closes fine, then I shouldn't worry about the rust on the inside of the knife.

This got me thinking that surface rust is mainly cosmetic, and that if it doesn't effect the function of the knife (such as by making the action gritty) then it isn't a real concern beyond looks. Is this true? Or will unremoved rust eventually rot out the knife?

Sorry for so many questions. You don't need to answer each one (duh). I am just looking to improve my general understanding of rust, how and when it occurs, how much I should worry about it, how dangerous it is, and what I can do to prevent it without going overkill.

Thanks in advance.

 

[Hair]

I removed the rust on my Mcusta using CLR. It got rid of the redish surface rust, but there are a few black specs left that won't go away. What are these specs? Are they dangerous? Or purely cosmetic?

I don't mind how they look. I just want to make sure they aren't "under-the-surface" rust spots that will spread and harm the knife. Even if they are purely cosmetic, I would still like to get rid of them if possible. Should I just leave the CLR on for longer? If I leave it on for too long, can it damage the metal?

 

[orthogonal1]

I was under the impression that CLR worked via chemical conversion.

Therefore, the "black" specks would be akin to magnetite, which would act as a barrier to prevent further oxidation (rust). Thats how it works in boilers and on older car frames, anyway.

You could try using a toothpick to remove the specks, then apply your choice of rust preventative (oil or whatever). I'm cautious of using chemicals around my knives as I have damaged the finish on a few, though CLR is relatively mild as these things go.

 

[Hair]

Thanks for the reply.

I don't think a toothpick would work. The seem to be a part of the metal.

They look like the black specks sometimes left behind after sanding off rust. I sanded some rust off an old slipjoint that sat in the garage for decades and one of the rust spots left behind a smaller, blacker version of itself. It looks very similar to what is left behind by the CLR on my Mcusta.

Also, I should note that the black specks are not everywhere that the rust was. Most of the rust is gone without a trace.

 

[Psychopomp]

Steel rusts. It's natural and as long as it's only surface rust, it won't hurt the knife. It should be dealt with as quickly as possible, but as long as the blade doesn't start to pit, it'll be fine.

It's very important to take care of your knives, as you would any tool. But you CANNOT be afraid to use them. It's an expensive hobby, and if you're going to spend the ammount of money that you will on knives, it's a shame not to use them.

As far as rust prevention stuff, I avoid it like the plague. I EDC a dedicated food cutting knife, but the need may arise that I need my larger EDC folder for food, and I don't want any added chemicals.

Wipe them down when they get wet, keep them in a dry place when not in use, and use them and enjoy them.

 

[yoda4561]

Militec is no good for rust protection, use breakfree CLP if available locally, or even a hard paste wax like renwax or some automotive waxes.

 

[kricket]

Birchwood Casey makes a product called Sheath or the new name is Barricade. This stuff is great, rub it on and rub it off. I learned about it from Burt Foster MS in Bristol, Va. Give it a try, also check the area where the rust started up so fast and see if there's a corrosive substance in the area. I had some alum. cleaner that was in a utility area and you couldn't leave anything metal in the room without rust starting the next day.:thumbup:

 

[Cliff Stamp]

1) I try to wipe off my knives with my shirt whenever they are handled, just to get any hand moisture off. I don't have any metal protectant yet, but I plan on getting some. If I use metal protectant on my knives, wipe them off after use, and try to keep an eye on them for rust (so I can remove it before it gets too excessive), will I have a pretty good game plan against it?

It depends on the knife, some steels can rust so fast that if you cut onions or similar with them, you can see the rust form during the cutting. L6 and O1 have this behavior for example.

2) With stainless steels, is it fairly safe to use the knife in normal conditions (including somewhat sweaty hands) and not worry about wiping it off after use?

There are wide differences in the stainless steels, some like AISI 420 are very corrosion resistant and you can let them sit wet, even with salt water and see no ill effects. Most will handle plain water well, it usually isn't an issue even for extended exposure, and exposure to salt water and food acids for a limited period of time, it usually takes hours of exposure to cause pitting on VG-10, ATS-34 etc. .

For example I recently did a soak on VG-10, left a H1 in the leather sheath overnight filled with rain water. After 6 hours there was no sign of corrosion, after 16 hours there were a few tiny spots (0.5 mm or so) and one cm sized light grey patch. It all came off with a paper towel. The edge still sliced paper well and caught on a couple of sections where the spots had hit the edge.

3) With carbon and stainless steels, how much do you need to worry about rust? Of course they rust easier, but is it so extreme that you must dry the knife immediatly after getting wet? Can I use them without wiping them down? Or is drying them (of normal hand moisture) after each use very important?

Some can rust this fast, I have done comparisons with large knives in the rain for example, and watched rust form on 5160 blades just in the minutes inbetween use. Your enviorment matters a lot, how close are you to the sea (salt water) how hot it is, how humid is the air and some people have very acidic sweat.

4) If a knife gets some rust spots, and the spots are removed with a metal polish or rust remover like MiliTec, are there any long term affects?

Yes, the surface now has the depressions left from the rust and it will rust easier there in the future. If you clean a really rusty machete and compare it to a new one you can readily see the difference if you leave both out in the rain.

If someone didn't take care of their knife and had to keep removing the rust over and over, would the knife eventually "die"?

Yes, in general excessive rust removal can be as bad as inducing it in the first place. Generally wipe them down aggressively with a cloth, or lightly with an abrasive, constant sanding and chemical removal will lose more steel than oxidization. You generally only need to be this aggressive repairing a heavily rusted knife you found in someone garage for example which will never be exposed to similar conditions again.

5) How much rust is bad for the knife? Are rust spots mainly cosmetic? At what point does rust become a matter of the knife's health and function and not just looks?

Rust converts steel to iron oxide, which is far weaker and more brittle, the more it happens the more your knife loses its strength and toughness. If it happens even slightly on the edge the performance drops off very quickly because those sections break away almost immediately in use.

-My Mcusta has some spots of rust on the scales. Do I need to worry about these right now (i.e. get some Militect tomorrow and remove them ASAP) or can I leave them for now and get some Militec when I get a chance? Will the rust spread? After I remove the rust, will the knife be as good as new?

Rust comes in two forms, the soft orange kind and the hard black kind, it isn't alive in the sense that it grows from itself and you need to kill it. If you remove it from what is causing it to rust, it won't keep forming. The orange rust is more problematic as when it changes the steel it causes a volume increases which induces flaking, this is why it is easy to wipe off. You want to get rid of that, just use a light abrasive, or even a cloth and hard scrubbing.

The black spots are also rust, but it is hard and stable, it will also act to prevent the orange rust from forming (to an extent) and will eventually form a solid coating on non-stainless blades after years of use, this is why really old blades will be basically black naturally. People will often induce this on new blades causing a patina to form, others just watch it happen with normal use. 1095 does this fairly quickly.

-I have a Hen and Rooster stilleto that has some rust on the liners. It isn't on the "face" of the liners (where the blade goes when shut), but rather on the sides. So you can only see it when the knife is open and the liner moves into the locked position. Will this rust eventually compromise the liner lock and should be removed ASAP? Or is it mainly cosmetic and not a worry if I don't care about it?

I have a slipjoint that was in the garage for decades and got some rust on the blade and inside the liners. I asked about how to remove the rust and a couple people suggested that if the knife opens and closes fine, then I shouldn't worry about the rust on the inside of the knife.

Surface rust only penetrates a little into the depth so it weakens only a small percentage, however if kept in the same enviroment it will keep moving down into the steel and eventually weaken it. But if you just apply a protectant over the top of loose orange rust, the rust can flake off leaving unprotected steel which is why you clean first.

-Cliff

 

[Hair]

Thanks guys! I have learned a lot today!

I won't worry about the black spots on my Mcusta, as they are hard to notice and don't bother me much. But I assume that if I ever was so inclined, they could be removed using rust remover? Perhaps the CLR should have just been left on longer to get rid of the black spots?

 

[Cliff Stamp]

Chemical agents will remove the black oxide readily.

-Cliff

 

[Zemapeli]

I had the same question exactly. There is no real perfect way to remove the black oxide from a metal pit but by removing medium from the blade itself, making the base of the oxidized pit flush with the rest of the blade. (this is the Pit in the metal, or where it was eaten away by oxidation) This works, but thinning out the blade isn't exactly a great thing for the knife either, so I guess it comes to good judgment on the lesser of the evils when it comes to rust removal. The only ways to get real results (in my humble opinion) are to use a metal finishing pad and 1000grit wet/dry paper with oil and a lot of sanding, while being careful not to blemish or ruin the lines of the knife. I have also used CLR, which seemed to work to some extent. However, with CLR (which is actually a type of acid), the whole blade becomes a bit oxidized when it is treated. Also, if you leave the metal in the CLR wash for long periods of time, it will oxidize and pit the blade horribly. I have ruined a knife this way before... live and learn. I have also used a product called Naval Jelly, which is basically the same thing as CLR but pink, thicker, and more concentrated. Almost like comparing Bengay to Tiger Balm. Again, same results with the Naval Jelly as with the CLR treatment, but stronger, and it will also oxidize the entire metal surface you are treating as opposed to just removing the oxidized spots you want to remove. I have heard about a way to remove rust using electricity (called "electrolysis") as well, however I have never tried this.. Seems a bit too taboo and complicated to me, but you could try googling it if you like. I have never tried automotive agents or anything of the sorts. Might be worth a try, but use a little on a test spot as control. those black pits on some of my knives bother me a great deal. Then again, maybe I am just OCD about rust. Either way, If someone found/invented a way to remove the black oxides completely from metal pits and turned that into a product, they would definitely make a killing. Best of luck.
Never know.