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The Outpost This forum is dedicated to all who share a love for, and a desire to make good knives, and have fun doing it. We represent a diverse group of smiths and knifemakers who bring numerous methods to their craft. |
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#1
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Dissimilar metals cause corrosion
In all the years I have been on knife making forums I have not read any info about dissimilar metals. The materials we use to make a knife can actually accelerate the corrosion of steel. Metals such as nickel, silver, copper, stainless, brass and bronze in a moist enviroment can react with iron to make a very weak battery. This translates to corrosion which carbon steel is very prone to in the best of enviroments.
"When two different metals are in contact in a corrosive environment, one of the metals experiences accelerated galvanic corrosion while the other metal remains galvanically protected. Galvanic corrosion occurs when two different metals are in contact in a corrosive environment: one of the metals (The carbon steel blade) experiences an accelerated corrosion rate. The contacting metals form a bimetallic couple because of their different affinities (or attraction) for electrons. These different affinities create an electrical potential between the two metals, allowing current to flow. (ie; rust)" -American Galvanizers Association. Nickel is one of the "worst" ones since it is highly reactive. The two types of rechargable batteries we commonly use are nickel based, Nickel cadmium (NiCd) and nickel metal hydride (NiMH). By being aware of this potential reaction we can insure our knives will be around long after we are gone. The possibly un-informed customer will not think about galvanic corrosion they will just chalk it up to the maker using inferior products and techniques. Your knife might be able to chop through two 2x4's, a 1" rope and still shave arm hair and then be bent to a 45 degree angle but what good is that if it rusts a few years down the road? That nickel silver or stainless guard looks pretty on that new knife but think about it's future. Here is a picture of a stainless(?) knife that was put in the drawer and contacting a carbon steel knife while they were both damp. The carbon steel knife had serious pitting but it also electroplated the stainless knife. This is after I went over it with steel wool. They were in the drawer for less then two weeks. Last edited by B.Finnigan; 10-23-2006 at 06:44 PM. |
#2
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Oh Boy!
Sounds like a juicy topic for another gut wrenching thread! ...Good point! |
#3
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check the search function.i believe this subject was discussed at length more than a year ago.
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#4
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sounds ilke a job for mythbusters!
seriously tho what was the outcome of the treat a year+ ago? Ed __________________ Gold is for the mistress - silver for the maid Copper for the craftsman cunning in his trade. "Good!" said the Baron, sitting in his hall But steel - cold steel is master of them all. Rudyard Kipling (1865 - 1936) |
#5
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I searched "galvanic corrosion, corrosion and dissimilar metals" and found nothing. It would be great if we could have two different search functions, one for advertisers and one for raw info.
Many months ago a knifemaker posted a question in the Newbies forum why his knife had greenish blue staining on the blade. He used nickel silver and a copper spacer. Alot of people commented that it was copper corrosion but nobody went into any detail why it happened so quickly. I touched briefly on galvanic corrosion but no one else chimed in with any additional info. It was sort of a digital "deer in the headlights" reaction. If the knife you make is going to be in a humid enviroment especially in a coastal area this really needs to be addressed. It will happen, the question is how fast and to what extent. |
#6
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I guess there might be something to be said about integral guards and wrapped integral socket handles...
No dissimilar metals here. You get corrosion from dissimilar metals aggravated by a little hydrogen embrittlement from acid etching and all hell can break loose! The blade can literally rot off at the guard... Last edited by Tai Google; 10-22-2006 at 05:28 PM. |
#7
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so basicaly the first image that was posted had some type of chemical on it to start with.
Also anyone have a list of reactions each metal has? __________________ Gold is for the mistress - silver for the maid Copper for the craftsman cunning in his trade. "Good!" said the Baron, sitting in his hall But steel - cold steel is master of them all. Rudyard Kipling (1865 - 1936) |
#8
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The first pic is a stainless steel blade that reacted with a plain carbon steel blade due to a small amount of dampness. The two blades were put in a drawer with the blade tips touching when niether of them were dried off completely. No chemicals were involved except H2O and a very weak current of electricity. Seven year olds don't always do the dishes correctly.
Last edited by B.Finnigan; 10-22-2006 at 07:19 PM. |
#9
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that photo actually looks like something I would see on a dive boat after a weekend of diving. only difference would be the dive boat thing would have it wide spread.
I did run across some charts and some very fascinating info on this. Quote:
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__________________ Gold is for the mistress - silver for the maid Copper for the craftsman cunning in his trade. "Good!" said the Baron, sitting in his hall But steel - cold steel is master of them all. Rudyard Kipling (1865 - 1936) |
#10
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This page explains the anodic index and galvanic series pretty clearly: http://www.corrosion-doctors.org/Def...nic-series.htm
__________________ Perfection is a process, not a goal. Perfection is a journey, not a destination. |
#11
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The electrolyte series is a little deceiving - distilled water is very corrosive as it has no buffering.
__________________ God bless Texas! Now let's secede!! |
#12
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I'm a little confused here because I was under the impression that the nickel in 15N20 and L6 played a notable part in the corosion resistance of those metals. 15N20 in particular seems to be pretty much a plain-jane carbon steel with a little nickel added. It seems to rust much slower in our humid environment than 10xx series or O-1 steels seem to. Is this because they are in a "solution" of some sort and there is no surface for an electrolytic reaction or am I missing something here?
__________________ Cap Hayes See my knives @ knives.caphayes.com This quote pains me: -- "Strategically placed blood grooves control blood spray in covert deanimation activities." -- |
#13
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It could be that you keep them oiled adequately. I have had some pattern weld billets that I did not like the patten so I pitched them in the scrap pile and they rusted within days. That is with only 1.5% nickel. Alot of stainless has 8-10% Ni.
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#14
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One of the jobs I had years ago was doing all the flat stainless steel in the galleys of super tankers. The stainless steel fastend to steel furring. Before I attached the stainless I had to run a strip of plastic tape to the furring to stop the electrolisis.
As soon as I posted this I just happend to think that I used stainless steel screws to hold the pannels on. Nothing was done to stop the electrolisis for that application. Last edited by Raymond Richard; 10-23-2006 at 05:07 PM. |
#15
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ooops!!!
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