Post By Lew Hartswick
Electrolysis And Hydrogen Embrittlement
On a motorcycle forum I visit a person asked about removing rust from some engine, transmission and clutch related parts and I mentioned using electrolysis.
Needless to say every reply was negative saying the parts would have to be reheat treated or the part would be ruined or unsafe and so on.
I've used this process a lot in the last year or so and have never run into any problems what so ever, but I'm not a chemical engineer either.
Is it bs or true?
Anodic electrocleaning, which is the most common way to electroclean, doesn't produce hydrogen embrittlement. These folks at the motorcycle forum are just trying to show their knowledge of fancy sounding terms they dont understand.
I'd bet those same guys are all keen on "billet" material to make parts out of. :-)
Originally Posted by E. Bobicki
This article may help with the problem of embrittlement. I have never seen any parts that got brittle from electrolysis but this article does mention how to safeguard from it, toward the bottom of the page.
We deal with this problem all of the time. Most of the problems are alloy dependent. Some alloys have an affinity to hydrogen and others are not as bad. Chrome-moly alloys seem to be the worst. We require a "hydrogen bake" of 850F after weld or plating on those alloys. Mild steels are usually not a problem.
what about cast iron JR
should i be weary of doing hubs and calipers etc off cars ...
wont even think about brake drums and discs
all the best..markj
The electrolytic rust removal process does produce hydrogen, but most of it is driven off when produced. If I understand the biggest danger of hydrogen embrittlement, it is on parts that have been plated, the plating holding the hydrogen.
The most susceptable metals are the higher alloy steels, mild steel and cast iron should not present a problem. Baking is a belt and suspender approach to remove any concerns.
Hydrogen is produced at the cathode, this would be the scrap piece you put in the bucket while electrocleaning the item of interest on the anodic side. Anodic cleaning will strip metal if you leave it in too long or the metal is not compatible with the pH of the cleaning solution (ie caustic soda and aluminum)
In plating the cathode is where the hydrogen is produced and the metal is reduced onto the surface, plating parts can cause embrittlement, and a bake is required. Anything over 500F is enough but it depends on the metal I guess, I know little about baking to remove hydrogen from plated parts.
In electroless plating there is no anode or cathode and the hydrogen is produced on any metal part in the solution by the hydrides in solution(the active ingredient).
I had a coil spring with tension on it break in the electrolisis tank. Why it happened I dont know for sure but hydrogen embrittlement sounds like it could be the cause. As I understand the hydrogen will leave the piece over time but leaves faster with heat. Someone mentioned paint holding the hydrogen in. It may slow the transfer but it would not stop it. I had a body pannel from my '54 truck in the electrolisis tank for almost a week. I had to do some hammer and file work to smooth out a dent. I did not notice anything strange about how the metal behaved. How could a piece be tested for hydrogen embrittlement?
they are worried about Hydrogen Embrittlement and then they go and chrome every thing?? lol
Lazlo, anodic electrocleaning is the prefered method, it is also applicable to stripping old plating in the proper bath. It may be called reverse because it is the reverse of plating current flow.
The only time one would use cathodic cleaning would be if the surface cannot be altered in any way, and if this would be the case other methods would be used instead as cathodic cleaning isnt terribly effective, it relies on the action of the bubbles and the chemicals in the bath alone and not on the electrolysis dissolving rust and oxidation.
But the problem is that most home-shop types, including (I gather) J. Ramsey, use direct, or cathodic electrolytic rust removal, which does generate a lot of hydrogen from the workpiece, and may in fact be subject to hydrogen embrittlement.
Originally Posted by E. Bobicki
Yes, the current fad of electrolytic rust removal is cathodic--the workpiece is the cathode. As was mentioned several times previously, hydrogen embrittlement is really only a concern for some high strength steels, and there is a way to mitigate it.
Originally Posted by lazlo
The problem with hydrogen is with steels that are harder than C44 or so and the parts or under stress. The stress could be either applied as under load or it could be trapped stress as in the case of quenched that hasn't been tempered.
This from Wikipedia
"The mechanism starts with lone hydrogen atoms diffusing through the metal. At high[clarification needed] temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible. Austempered iron is also susceptible. Steel with an ultimate tensile strength of less than 1000 MPa (~145,000 psi) or hardness of less than 30 HRC are not generally considered susceptible to hydrogen embrittlement. Jewett et al. reports the results of tensile tests carried out on several structural metals under high-pressure molecular hydrogen environment. These tests have shown that austenitic stainless steels, aluminum (including alloys), copper (including alloys, e.g. beryllium copper) are not susceptible to hydrogen embrittlement along with few other metals. For example of a severe embrittlement measured by Jewett, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen.
Hydrogen embrittlement can occur during various manufacturing operations or operational use - anywhere that the metal comes into contact with atomic or molecular hydrogen. Processes that can lead to this include cathodic protection, phosphating, pickling, and electroplating. A special case is arc welding, in which the hydrogen is released from moisture (for example in the coating of the welding electrodes; to minimize this, special low-hydrogen electrodes are used for welding high-strength steels). Other mechanisms of introduction of hydrogen into metal are galvanic corrosion, chemical reactions of metal with acids, or with other chemicals (notably hydrogen sulfide in sulfide stress cracking, or SSC, a process of importance for the oil and gas industries)."
This article says C30 or above is susceptible. In may experience it is more in C40's range.
Every time this comes up, there is a lot of confusion about where hydrogen forms.
Originally Posted by lazlo
The anode is positive and electrolysis breaks down water into oxygen there. Oxygen does other sometimes undesireable things, but does not cause embrittlement.
The cathode is negative, where hydrogen is formed from the water.
Anodic electrolytic rust removal does not generate hydrogen on the part.
There are rust removal systems that generate hydrogen under the rust and mechanically pop the rust off. These are cathodic systems and can cause embrittlement.
In a plated part, the hydrogen that you worry about is in the steel. Whether or not there is any in the plating is not that important.
Paint is not going to be a barrier to hydrogen atoms.
I can tell you from my own tests that hydrogen embrittlement is very real. It is most important on a thin part where the brittle layer is large compared to the total thickness, but it can also promote the start of a fracture in a thicker part.