Electrolytic Rust Removal - Hydrogen Embrittlement Concerns

[JTinAZ]

I have taken everything apart from the FJ40 and the mini-truck axle for my disk brake conversion. I am considering the electrolytic process to remove rust from the knuckle housing. For you electrolytic experts out there, do I need to be concerned about hydrogen embrittlement? Also, the spindle that slides over the birfield shaft has some sort of plating inside. Any effect on that if I go ahead with the electrolytic? Thanks.

Another question: When I am done cleaning, what do you think about painting the knuckle housing (tacky, don't worry about it, ect.)?

 

[Pin_Head]

I am only familiar with hydrogen embrittlement in welding, where hydrogen is absorbed by molten iron. I don't think you are going to get it that hot.
The spindle has a bronze bushing, but I am not aware of it being plated.

Paint looks nice and I think that they came painted from the factory.

 

[JTinAZ]

You are correct. I believe that's bronze in there.

 

[CruisinGA]

Is it that rusty that you can't get it clean enough with a wire wheel, etc?

Seems like a waste of time to me and I have done dozens of knuckle rebuilds and a few disk brake swaps.

If you got the time, go for it.

 

[Benson]

I've been looking into this. Have you read these?

http://myweb.tiscali.co.uk/andyspatch/rust.htm

http://www.stovebolt.com/techtips/rust/electrolytic_derusting.htm

Also check birfield.com. There was a lengthy discussion on it about a year ago.

And don't forget Coolerman's website. He's done a lot of testing on different methodologies:

http://www.globalsoftware-inc.com/coolerman/fj40/rustremoval.htm

Good luck. And let us know how it works.

 

[Gumby]

I ERR'ed my knuckles on the 78 40 and it worked great. Don't do the spindle. There's really no need and the ERR will eat the bronze.

 

[largenfirm]

I've used electrolytic rust removal on old edge tools (chisels, saws, etc), and found that it does cause hydrogen embrittlement, but the solution is a 2 or 3 hour "soak" in a warm oven (250-275 degrees F) to drive off the hydrogen.

If you don't do the roast, chisels and saws will break, based on personal experience.

Be sure to put some rust inhibitor on the parts before roasting, however, or they will come out covered with fresh rust! I use paste wax, generally, although a dip in a paraffin wax bath works fine, too. Don't use WD-40.

Kirk

 

[JTinAZ]

I wouldn't be so concerned about the embrittlement or throwing it in the oven if it was not a drivetrain-related part. That's all. I've checked out the websites mentioned above. They are the ones that mention the brittle issue.

 

[Old Blue]

When this topic popped up on the LCML, I chimed in with my concern for hydrogen embrittlement. I wouldn't do this on a part that will see continuous stress, as in a tightened bolt. Knuckles should be okay, but someone was dipping there entire front hub with lug bolts. That scared me.

As you may know, hydrogen is produced as a byproduct of the anode/cathode reaction. Hydrogen will seep into the grains of the steel, and may decide to hang around if not forced out. Coating the part with paint/zinc plate/cadmium plate will most certainly trap the hydrogen. Baking the part, as someone mentioned, will drive the hydrogen out of the part. If the hydrogen remains, the part may experience a brittle type failure if under continuous stress, like a torqued down bolt. There are ASTM standards for the bake operation which are adhered to when producing plated parts. I'm not sure if hydrogen embrittlement effects cast iron the same as plain carbon steel, that's beyond my knowledge. Be careful of bake temps, because the last thing you want to do is temper back the steel and modify the physical properties of the steel.

My rule of thumb is that if there is no safety concern, then I go for it. Just like welding. I'm not a professional welder, so I probably wouldn't weld critical parts on my cruiser. This of course is my opinion, and I tend to lean towards the safer approach anyway.

 

[Pin_Head]

I can't see that hydrogen embrittlement would be a problem in this application because it is not soluble in steel below the austenitic phase transition temp of steel (~1500F). It is produced by the electrolysis of water and this only occurs at the surface. The hydrogen goes into the water, not the steel. If hydrogen was soluble in steel at room temperature, then you wouldn't be able to store it in steel cylinders at 2000 PSI.

 

[billmc]

As a practical example of non-embrittlement, I used ERR to clean up the very corroded rear stabilizer bar and frame brackets (as well as the fasteners) 4.5 years ago. With all the stress on those parts, any brittleness would have shown up by now.

I'm much more interested if the low energy levels involved with ERR can really produce meaningful amounts of hexavalent chromium when S/S is used as the electrode.

Bill

 

[Pin_Head]

Hydrogen comes out of the weld metal pretty fast even at room temp. One of the excercises we did in welding class is to put a high H weld in a pan of water with a glass bowl full of water over it and you could see the H bubbles coming out. It was all done by the end of class (3 hr) with 1/4 inch steel. That's why H embrittlement isn't a big issue on welds less than an inch thick.