For welding, pipe fitting, plumbing or other work with metal, you need to be able to tell the difference between cast iron and cast steel. Cast iron is cheaper, requires less energy for casting and has a lower melting point than cast steel. Cast steel is more reliable for more complicated castings because it is more flexible and has a higher resistance to tension than cast iron. You can perform tests to identify between the two metals, some which are slightly destructive. If you do not want to tarnish any of your material, you may be able to tell the difference through simply looking at the metals.
Identify the metallic material by looking at its raw surface colour. The surface of cast steel is dark grey, sometimes referred to as "steely." In contrast, both white and grey cast iron have a duller and less shiny grey appearance.
Perform a spark test by holding the edge of your metal sample against the cutting edge of a grinding wheel. If the metal generates red sparks, it is cast iron and if it generates white sparks, it is cast steel.
File a piece of metal off your sample using a metal file or a chisel. If it is cast steel, you should be able to file a continuous chip. For cast iron, you will only be able to file small chips of metal off.
Perform a melting test if you have extra metal to work with. Hold a blow torch to your metal sample after putting on your safety gloves and mask. Observe the colour of light that surrounds the metal as it melts. Cast iron appears red as it begins to melt and cast steel appears white. This is because cast steel melts at a higher temperature than cast iron.