Does CrMO rust?
 

I read about protecting your frame from rust. However my bars a CrMo and they don't rust so why would my frame which is also made from CrMo steel rust? Are there different types of CrMo? Or are different parts of the frame made from other materials that can rust? Huh?

CrMo is chromoly, a steel alloy with Cr (Chromium) and Mo (Moly-something... grab a periodic table..) and it can rust, just as stainless steel can rust. How do you know that your CrMo bars don't rust? I have CrMo bars that haven't rusted, but that doesn't mean that it can't rust.

Usually there is some kind of corrosion prevention used, such as paint for your frame, but if the frame or parts are really important to you and/or expensive, something like "framer saver" would be prudent.

I thin pretty much everything with steel can rust and most other metals and/or alloys that may or may not have steel will corrode in some way. Except for that steel tower in the Middle East somewhere that has been outside for more than a thousand year... I think the Arabs somehow made a true rust-proof steel. Too bad the art has been lost, like Greek fire.

Stainless steel, and there are many varieties, more "pit", than rust, as we generally know it.

Most alloys that comprise steel will ultimately turn back into the basic components

from which they were made by the formation of rust by either oxidation or mild electrical

reaction; iron being the dominant player.


Regards,
J T

Yes there are different types of cr-mo (chrome-molybdenum) steel. The amounts of chromium and molybdenum in the steel varies but is usually very small (1% or less of each). There are also other elements alloyed in there and different ways of making the steel. Stainless steel has a minimum of 11.5% Chromium.

CrMo will certainly rust, I have some old rigid mtb frames in my basement to prove it.

I just took some rust off an old machine that went through the winter and never got cleaned.

It is a Chro-mo frame... so that just proves it rusts..

Your bars haven't started rusting yet because.... you keep them clean and/or they probably have never hit any salt water, which acts like a catalyst.

Keeping things clean helps prolong the oxidation.

Judging from the Rust on my CrMo Trek out in my garage, Id say yes!

Luck, perhaps? If the bars are painted, it could be that they didn't get scratched whereas the frame did (which would be a good way for the rust to start). Or possibly they're rusted under the paint and you don't know?

In any event, CrMo definitely rusts.

Your bars were either painted, plated or coated with one of the newer bake-on coatings.

Unprotected Cr-Mo (and yes, there are several grades) most definitely rusts. The Cr and Mo content are there to provide strength and the levels are much too low to provide rust protection. As noted above, strainless steels have a minimum of 11.5% Cr and most have 13 to 18% Cr.

By "bars" I assume you mean handlebars. Have you looked inside them? Most steel HBs I have seen are chrome plated on the outside, which is a pretty good rust inhibitor, but are plenty prone to rust on the inside.

Yes, Cro-Mo will rust.

Check the place your handlebars connect to your stem. What about inside of the handlebars? Ok the handlebars could be not rusted. I have seen a rusted crmo frame. I'm sure if you really look for it you will find some rust in the frame somewhere. If not throw into the sea if you have one nearby and come back for it in 5 weeks.

Rust appears in the places most people don't bother to look.

CrMoly is only rust resistant. It is actually self passivating like Al. If it is scratched with ferrous metal it will rust at that point. Also different grades of CrMoly or stainless used together with cause oxidation

The typical "low alloy high strength" steels that include the usual Cr-Mo grades used in bicycle frames are not self-passavating as the Cr content is much too low. The higher Cr (and sometimes Ni) content of true stainless steels does make them self-passivating.