I am interested in comparing the different materials that can be used to make castings of cast irons, and therefore was wondering which material is commonly used/which materials can be used to make permanent casting molds (to be used specifically for cast iron). Thank you.
You can cast iron into cast iron moulds as long as the moulds have plenty of mass compared to the quantity of metal you are pouring into them. Small artisan foundries sometimes use cast iron moulds to make small ingots as a 'signature piece' to use up small quantities of surplus metal. Often these are open face moulds.
Obviously steel works as well but steel moulds tend to be significantly more difficult to make.
Typically in industry multiples of the same casting are made in green sand moulds using a pattern which is pressed into the mould which means that although the specific mould is broken up after each casting the sand can be reused and it is fairly straightforward to mass produce moulds.
With metal moulds you need to be quite careful about draft angles and avoiding undercuts. Shrinkage stresses can also be a problem with more complex and hollow shapes which can end up too constrained by the mould.
You may also need to allow additional venting compared to sand moulds as unlike sand gasses can't escape into the walls of the mould