Cast Iron Tensile Strength

[brakemeister]

I am working on a disc brake rotor/hub application which uses a cast (I presume green sand) gray iron as the material. Notwithstanding impact or shock loading which could only occur during a crash, does anyone know of a reason why 37,000 psi cast gray iron would be inferior in performance to a lower tensile material such as 25,000 psi gray iron?

 

[TVP]

Corrosion, fatigue, etc.

 

[Metalguy]

TVP,

Corrosion resistance should be the same, while fatigue properties are better for higher strength CI.

 

[arunmrao]

A high strength CI means a lower carbon equivalent iron, and vice cersa for lower strength cast iron. The latter may be preferred for the application as the amount of graphite flakes would be higher .
This would result in better damping properties and dry lubrication(due to the presence of more graphite). Also the machining of these castings is easier.

 

[NickE]

Also governing the strength of the grey iron is the morphology of the graphite flake. The clas 25 grey iron will have larger flakes with more uniform and less branched/more elongated structure. The larger graphite flakes should provide better machining properties as arunmrao states, also the matrix is probably softer due to differences in solidification rate/conditions.

As to noise damping I would venture that For the same %vol graphite the more branched and bettter distributed graphite flake will provide better damping/ also quite possibly better differential heating performance.

Though it is common that as arunmrao states that the lower strength iron has a higher carbon equivalent.



Nick
I love materials science!

 

[rbigge]

The higher strength iron will have lowewr damping capacity and lower heat capacity. This could cause increased noise and reduced life from heat checking especislly if used in hard braking condition.

 

[gdodd]

In addition, the higher strength graphite contains a predominantly pealitic matrix which imparts a degree of wear resistance and strength. It is normal practice to restrict the amount of ferrite in the microstructure to ensure the good wear resistance. This is achieved by adding carbide forming elements to the recipe such as copper and chromium.

 

[TVP]

gdodd,

FYI, copper does not form a stable carbide compound. C has very low solubility in the Cu FCC lattice, ~ 0.01%, and the rest of the phase diagram is Cu + C. Cr & Mo are the most common carbide formers in iron and steel alloys. Cu promotes pearlite formation and has a potent strengthening effect on the BCC iron lattice, similar to Ni.

 

[boggyB]

ALL COPPER DOES IS PROMOTE PEARLITE AN ADDITTION OF 0.5 TO 1% WOULD GREATLY INCREASE THE LIKELY HOOD OF A FULLY PEARLITIC MATRIX.
AN ADDITION OF 0.5% CHROME AND 0.2 % MOLY WOULD CREATE VERY STABLE CARBIDES....!!!