Blued Rotors - at what temperature?

[260DET]

What temperature would rotors have to reach to become blue on the pad contact surfaces? Other than the possibility of warpage, is there any damage done to to the rotor metal itself in reaching such a temperature?

[RESON8]

Not exactly sure but i remember in a cutting tool test at uni the steel we were machining would turn blue at around 500-600degC

[dbasteve]

Temps above 450 Deg C will start to turn cast iron blue.
Whether or not any damage is done depends on how you get to this temperature. If you bring the temperature up gradually it wont cause any significant damage. Obviously if it is done on rotors/pads that aren't bedded in properly or cold rotors the temperature spikes can greatly affect fatigue and distortion in the disc.

[rodhog]

My disks are almost constanlly at this color. I go through brake pads about every 6-9months. 600dergee pads I'm told but with fade at blue stop the car but not that well

but I get mixed reaction, Like some times it will warp the discs usually when they are a really dark blue purple or they just don't react

Anyone know what colour a disc should be when at it's best temperature, for max performance.

[dbasteve]

The colour of the disc braking surface depends on the type of pad being used.
*NAO (non asbestos organic) pads generally have a light straw colour with a polished look on the disc.
*Alumina Kevlar Semi metallics (Ultimates) leave a black/blue colour on the braking surface.
*Carbon metallics (Ferodo) more blue than black.
*Carbon Ceramics (SBS, Carbotech) are back to a light straw with purple edges.

So the colour of the braking surface is really dependant on the pads being used. You can get a better indication in the non contact areas close to the pad area or the ideal for performance applications is to use heat paint.

Most standard street pads work best between 150 to 300 deg C and start to break down around 350 to 400 deg C.
Performance pads work best around 250 to 400 deg C and track pads 300 to 550 deg C.
These pads can handle higher temperatures than this but generally with lower performance from glazing and lower friction.