Safe rotational limits of 4E cast iron?

I have a 150mm disc ~24mm wide that I am intending to use on my bench grinder as a lap. The cast iron is 4E grade. Before switching the 2800rpm machine on I thought it best to see if anyone knows the safe rotational limit? I did some reading on car flywheels which are much larger and rotate much faster but they are likely a different grade of cast.

Any thoughts on the safe rotational limits of 4E?


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