Coated vs bare rotors

[Stubby79]

The black coated ones I've tried seem to have worked. Not sure if it's powder coating or what. The zinc and the cadmium (?) coated ones only worked for a year or so.

[Ecky]

I've tried both zinc and "black" coated ones. My last set for the stock brake size were zinc and after their first winter (5 months of intense salt) they still looked pretty good. I felt good enough about them I went with zinc coated for my new brake setup as well.

[freebeard]

Here's what I did:

Originally Posted by DDG

Cryogenic hardening - Wikipedia
https://en.wikipedia.org/wiki/Cryogenic_hardening
Cryogenic hardening is a cryogenic treatment process where the material is cooled to approximately −185 °C (−301 °F), usually using liquid nitrogen.It can have a profound effect on the mechanical properties of certain steels, provided their composition and prior heat treatment are such that they retain some austenite at room temperature.

It basically doubled the price of the raw parts, should get 3 to 4 times the service life.

edit: I went out to the carport and checked, they have some light scoring and discoloration (not rust) in eight years.

[ksa8907]

Never heard of that before, looks very interesting!

[Shaneajanderson]

Originally Posted by Daox

Other brands claim this coating helps the rotor not seize to the hub. I have run into this twice on Fords where I had to beat the rotor off the hub which broke it into pieces.

I always put some copper based high-temp anti-seize on the back of the wheels and rotors/drums where they contact to prevent this. It has work like a champ for me, even on the horrid railroad pickups with their 60 pound steel truck wheels. I remember it taking two guys beating the wheel with an 8 lb sledge each to get them off. Anti-seized them and next time they came right off without so much as a tap.

edit: you should be able to see the contact points pretty easily, they should have some sort of witness mark. I'd post a picture for you but i'm computer illiterate outside of excel, and never have figured out the picture thing here.

[freebeard]

Originally Posted by ksa8907

Never heard of that before, looks very interesting!

The process is popular with police maintenace departments and racers (like Porsche)

It's a general process that can apply to any part subject to wear or stress, up to complete assembled engines. Apparently it doesn't affect rubber seals, etc.

[Piotrsko]

All cryogenic should do is stress relief without softening like the ditto heat process does

[freebeard]

All cryogenic should do is stress relief without softening...

I've provided sources. This is a good one: thefabricator.com:Cryogenic processing—dispelling the myths, mysteries
Cooling your tooling for improved wear resistance, compressive strength

Figure 1: The leftmost diagram illustrates a theoretical cubic structure. Two cubic steel structures are body-centered cubic (BCC), also known as ferrite (second from left), and face-centered cubic (FCC), which is austenite (third from left). The face-centered tetragonal (FCT) structure, far right, is known as martensite. The FCT structure is about 14 percent larger than the FCC structure.

It involves excursions above and below room temperature.

[Piotrsko]

Your articles basically state that the material basically becomes harder with less warp/breakage voids, and less movement when hot (aka stress relief). It doesn't indicate whether or not it is less prone to rust which was the intent of my comment.

[freebeard]

I went out and looked at the rotor in the picture I posted. There is no orange or brown rust (the worst kind) but it has a fine-grained web of discoloration. That's after eight years on the car. Some minor scuffing/scoring, but nothing you can catch a fingernail on.