Does galvanic corrosion take place in knives?

[Fujimo]

I know that on a boat one never fastens a stainless steel fitting with a brass or a bronze bolt or screw. If you do it, the stainless will turn to powder, eventually.

Does the same thing happen in knives with brass/bronze liners?

 

[Dr. Mudd]

Galvanic corrosion happens most efficiently in the presence of an electrolyte to facilitate the process, commonly sea water in the case of boats, but it can happen to a much more limited degree in some cases without an electrolyte, depending on the reactive potential of the metals involved. I doubt it would ever be a problem on knives unless one was kept wet or in salt water use.

 

[Fujimo]

While an electrolyte speeds the process, it happens from simple contact. Such as the time that my father in law attached his steel stove pipe to the side of his shop using copper wire. That stove pipe didn't last long.

 

[cybrok]

I don't think there will be a problem.

And if you work in an environment where there is sea water, you should get a knife designed for that anyway.

As for your father in law, was there any electric current or welding involved?

 

[Frank_Zuccarini]

The temperature that a stove pipe is likely to see probably played a role in it's corrosion, I'd guess. Plus, heating/cooling cycles may have caused condensation. Both phenomena may have accelerated galvanic corrosion.

Just a though................Frank

 

[Fujimo]

I don't think there will be a problem.

And if you work in an environment where there is sea water, you should get a knife designed for that anyway.

As for your father in law, was there any electric current or welding involved?

My collection runs pretty heavily to rigging knives. I'm a recreational sailor. It occurred to me that many of my rigging knives are stainless blades and springs with brass liners.

 

[Esav Benyamin]

It occurred to me that many of my rigging knives are stainless blades and springs with brass liners.

Perhaps the contact needs to be permanent or at least longterm. The blade and liners of the knife are minimally in contact, if at all. Even knives with bronze washers and stainless blades don't seem to show corrosion.

Maybe the movement, opening and closing the blades, breaks the cycle, or the tight fit keeps the electrolyte out, or lubricants interfere with the process.

Brass guards and buttcaps aren't all that rare on fixed blades, either.

 

[STR]

All it takes as I understand it a conduit to let the static charge exchange back and forth between two dissimilar metals and that can simply be water and friction. I don't want to debate it with a bunch of folks but all I know is that with the proper ingredients, whether that be that certain mixture of metals, with water or some other thing like friction it can equal static I guess and you get this. I really don't want to suggest I can say with complete certainty what occurred here. Why is another issue and will probably always be a question left unanswered for sure but here it is in these two links.

If you look close you can see some spotting in places other than the pivot. Those are far enough away from the PB washers to make you think its just water spotting over time that was never dried off but the majority did occur around those washers between the stainless blade and the titanium handle liners. However, since replacing those washers with teflon ones I have not heard back that the rusting reoccurred. It may have reduced it some but I doubt any knife and especially folders regardless of type will do well if it isn't dried off or air blown dry after use around water. Perhaps the only exceptions to this are the H1 and X-15-T.N. blades in some Bokers and other makes of knives that have a nitrogen rather than carbon makeup.

STR

http://www.bladeforums.com/forums/attachment.php?attachmentid=72027&d=1179145990


http://www.bladeforums.com/forums/attachment.php?attachmentid=72026&d=1179145977

 

[Fujimo]

That's what I was thinking-that contact alone would be enough. The teflon washers seem to confirm the notion that the dissimilarity is enough to create a bit of galvanic corrosion.

 

[knarfeng]

Weeeellllll, it depends.

What brass? what steel? what conditions? Galvanic corrosion is a chemical reaction, and like most chemical reactions is subject to a lot of variables. And not all alloys react the same. The term "stainless steel" covers a lot of turf. For knives, I'll take it to mean ~14% chromium. For other uses I'd say stainless steel was in excess of 14% and could be in excess of 18% chromium.

The boat is an extreme case. You have electric currents from batteries and engines on boats and you are in salt water. You also have a very dynamic environment with fasteners rubbing against the fittings that hold them. This is a worst case scenario. You get problems there that you will not see anywhere else. (But I'm not sure that I would have a problem using brass and stainless even there. I suppose it would depend on what stainless someone wanted to use as some of the lower chromium grades might have problems. I would have problems big time if somebody wanted to use brass with galvanized carbon steel though. )

For galvanic corrosion to occur you need three things.
+ two metals that do not have the same electronegativity. We call these "dissimilar metals". The more dissimilar they are, the more stronger the drive toward corrosion.

+ contact between them. If the brass or bronze is coated, that coating might act as an insulator and might have to be penetrated.

+ moisture. Doesn't need to be a lot, but more moisture is worse than just a little. Salt makes the moisture worse. But remember that stainless steel has an outer oxide layer that protects it. Water has to get through that oxide layer and contact the actual metal.

There are a number of types of brass, but if I look in a galvanic series table, I see that the most common forms brass is dissimilar from most of the stainless steel alloys. But it's not tremendously dissimilar. The differenence is right about at the limit for what is considered acceptable. Titanium is far more dissimilar, yet we have no tales of knives dissintegrating when made with Ti liners.

I don't think brass rivets or liners causing corrosion would be an issue in any knife that is used away from a saltwater environment. And it might not be an issue then. Depends on exactly what grade of steel and exactly what grade of brass or bronze. Hmm. I'm repeating myself. That must mean I'm done now.

 

[Fujimo]

The most common alloy for fittings on a boat is 316 stainless. I agree that brass can be a lot of different alloys. "Tobin bronze" is even pretty much brass.