Welding Cast Steel
Casting is purely the means of creating the shape, same as forging and rolling. Therefore Cast Steel could be any grade from mild steel to Stainless.
Quite often it is something like En 24T mentioned earlier and, if it is, it should be welded in the same way.
If the actual grade is unknown E312 filler is good choice in that it is crack resistant and high(ish) strength (around 800 N/mm2).
Usually castings are non uniform shape (which is why they were cast) and this can create problems when heating (preheating) in that the thin areas will warm up quicker than the thick areas and expansion forces could cause cracks. Be careful if using a torch, heat it slowly give the thicker sections time to warm up.
Building up worn cast steel shaft. (E.T Brown and Son)
Manganese Steel
14% Manganese steel is often used for its work hardening properties. Dredgers seem to use a lot of it and so do Mixers.
It used to be called Hadfields Manganese Steel after the firm that invented it. Hadfield Steel was in Sheffield where Meadowhall Shopping Mall is now (no comment)
In the as cast state it will have a hardness of around 150Hv but by a little work (hammering or rubbing) that hardness will rapidly increase to 500Hv. So it can be machined to fine tolerances and will still withstand hammering and abrasion.
When welding onto it you must keep it cold. Use E307 weld metal and keep the runs short. You could stand the whole component in water to take the heat away or you can quench the weld in water. Heating this steel (by any means) makes the grains grow and the continue to grow until it loses strength and literally falls apart.