Steel is an alloy of iron with greater than 0.02 % carbon but less than 2%, and cast iron is an alloy of iron containing a even more carbon between 2 and 4%.
Cast iron (usually, but not always) compared to steel has:
Higher damping ability.
Higher thermal capacity.
Higher fragility/ lower toughness.
Higher castability.
Higher stability at higher temperatures.
Lower cost.
Lower machinability.
Lower electric conductivity.
Lower thermal conductivity.
Lower plasticity.
Lower coefficient of friction.
Lower density.