Cast Iron or Cast Steel, How do you tell?

You can distinguish gray cast iron from cast steel by hitting the casting with a hammer. The steel casting will ring; the gray cast iron will not. However, you can't use this method to distinguish ductile cast iron from steel.

In general cast steels will ring if you strike them, CI will 'thunk'.

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Rust never sleeps
Neither should your protection

If you have to grind out the crack for the repair, observe the sparks. Don't know about the newer books, but many old books had the spark appearance pictures in them.

If you are doing any weld repairs you should remove a small piece and have it sent to a metallurgical lab for chemical analysis.

If I was going to do any weld repair, you need to know what you are working with, period. As a side note, the chemical analysis would also tell you if it is a CI versus cast steel, based on carbon and Si contents. Also, if the material is even weldable.

I'm going to come out with some old timer type test.

With a very sharp small chisel get on a square edge and try to remove a thin chip using a very low angle on the chisel. It the chip curls or stay in on piece it is CS or DI. Cast iron will not form a chip.

I would run a weldability test, mainly for CI, by welding a small 1/4" 2x2 vertical tag to an inconspicuous area. After welding allow to cool and break the tag off the hard way, hitting from the weld side. If the tag bends you have a weldable material and it the weld cups out be very careful about welding.

Look at the raised letters on the casting and if you see WXX you probably have CS. CI not normally marked can have CI XX. somewhere.

As posted above sparking is a good way to help differentiate the materials. Get yourself a know piece of CI and CS and with a clean wheel look at the sparks, preferably in dim light. Let the wheel self clean itself on either part before comparing.

Learned a long time age that welding CI is art not welding. Use brush strokes, don't go for the penetration.