Dealing with pitting

While reading this good page linked in the Advanced Honing section by Neil Miller (SRP member), I found this:

Sufficient aeration (supply of oxygen to the reaction site) may enhance the formation of oxide at the pitting site and thus repassivate or heal the damaged passive film (oxide) - the pit is repassivated and no pitting occurs.

Could oiling an old blade with traces of pitting be a dangerous idea if pitting is not completely under control? But how to completely passivate pitting before oiling the blade?

I usually clean old blades just with some european substitute for MAAS (and with hours and hours of work). I use sandpaper (#600-2000 grit) just in case of active rust [as in "Dealing with rust"]. I guess that in case of pitting sandpaper is not a good tool.

I believe the article is referring to passivisation of Stainless Steel... most of our blades are carbon steel.

The process works like this: Stainless steel has a certain percentage of Chrome in it. The chrome atom once exposed to air (oxygen) quickly oxidizes to form an invisible protective layer of oxide (a passive layer), but this oxide layer is larger in volume than the chrome and iron atoms so is able to protect both atoms from further oxidation.

Carbon steel doesn’t have chrome (or not enough) for this process to occur so it will eventually rust without additional protection such as oil. However should it start to tarnish, oil will protect from further tarnish because the oil is a type of passive layer protecting from air (oxygen).

There is nothing wrong with sanding active pitting/rust on carbon steel because you will get rid of it, but the best protection is keeping it dry… and oiled if un-used for long periods.

Thank you!

I wrote that sandpaper is not a good tool just because you can not sand out the deeper point of important pits, so you don't know what will happen there and if corrosion is passivated inside the pit.

Try using a rust cutting oil when sanding, I sand dry, then spray some WD-40 on there, this creates a slurry just like when honing, which seems to get inside the pits way better.....

Thank you very much!! I will try to find something similar to WD-40 here.

Just to clarify I am talking about wet-r-dry sandpaper the black stuff....

Just about any automotive place should have a penetrating oil, something that is sprayed on rusted bolts to loosen them up.... Just be careful around scales I know the WD-40 is safe on everything that I have tried it on, excepting wood scales with a natual wax finish (beeswax) I haven't used it near those yet...

:gl:

Thanks for these important details too!

If the pits aren't too deep, haven't tried with really deep pits yet, you can usually just polish out the pits, tbh. The polishing compound will get down into the pits and after maybe...oh I don't know...a couple of hours of hand polishing, which you have to do anyway, the pits will be all nice and shiny. So if you don't want to go the sandpaper route, you might be able to polish the pits out. Might. depends on how deep they are.

Yes, that is what I usually do when polishing. In 4-5 hours everything looks shiny, but I can't stop wondering if corrosion is passivated. Now I think that using some penetrating oil will help me to sleep slightly better. eheh!