Hydrogen Embrittlement
?
*** WARNING! Science Fair project ahead!
"Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen." - Wikipedia
You can read more of the technical stuff on line. Key points to me are that hardened, high-strength steels (think saw chain cutters) are more at risk following exposure to acids (think rust removal).
Background
I am not a chemist, or a metallurgist. But when I had cutters from an older chain, that I had soaked in oxalic acid, crack when punched out of a chain loop, I became concerned that the acid treatment might be the cause of, or contributed to the cracking.
I looked around on line to get some information. Some articles/posts discussed differences between
mineral (hydrochloric, sulfuric, nitric, phosphoric, etc.) and
organic (acetic, oxalic, citric, etc.) acids. Some recommended heating metals to 350 to 400 degrees F for 4 hours, after removing them from an acid solution to remove excess hydrogen.
Again, you can read more about this stuff if you are interested. I wanted to find out if it was an issue for my rust removal procedures on chainsaw chains. So I retreated to "
Philbert's Research Laboratory / Laundry Room" to do some quick-and-dirty R-and-D.
Procedure
I took a single piece of scrap Oregon 91 chain, which was in good shape, with no apparent rust, but had the cutters worn off to the nibs. I punched/broke this into 4 sections and had no cracking of any cutters or tie straps in this process. I soaked these sections for 12 hours in one of four, different rust removal treatments (each has been described in earlier posts):
1. vinegar (acetic acid)
2. oxalic acid
3. EvapoRust
4. electrolytic (battery charger)
5.
citric acid EDIT: repeated this test with citric acid a few weeks later, with similar results)
(Note: I did not run any of these 10-12 drive link sections through nice, clean wood as a tratement, as they were too short).
After rinsing, and a light wire brushing, I baked them for 15 minutes in a 150 degree F oven to remove residual moisture - this is how I normally do it; not sure that I want to bake them for 4 hours. Afterwards, I punched out several cutters and tie straps from each sample, and compared them to the chain before treatment (making the sample sections) as the control. I deliberately punched more aggressively than normal to promote any cracking.
Results
No cracks developed in any of the samples.
I also did not notice any loss of chrome in the electrolytic sample, like I did with an earlier chain.
Discussion
This chain was not as old as the chain whose cutters cracked, and was not previously rusted. Older/different chains may have different metallurgy. Rust affects metal, and removing rust does not necessarily repair that damage. The chemical reactions with rusted chains may be different than those with non-rusted chains. It would take a quantitative lab, and a qualified metallurgist to do some real experiments and explanations.
Here are my findings/take-aways:
1. Some older, rusted chains may be brittle, or become embrittled by the rust removal method chosen. They may be OK for a display chain, but not necessarily a working chain.
2. To play it safe, use a weaker organic acid solution (if you use acid), and do not leave the chain in longer than the minimal amount required. Brush, rinse, and dry promptly.
3. Electrolysis may only damage chrome plating that is already weak or damaged(?). I will have to experiment with this more, but I would not use it on an older, special chain (e.g. a display chain) just to play it safe.
4. Some of these chains are essentially worthless without doing anything, so it still makes sense to try.
Philbert
opcorn:
