Ray,
Cast iron can be welded, but it then leaves it wide open to distortion and cracking, plus it will most probably have to be dressed back to original shape anyway.
The safest 'heat' method is either bronze welding or brazing, again the surfaces will have to be dressed back to original, brazing being the lesser of two evils.
If the parts are large enough you can have them 'stitched' using tapered straddle pegs. A repair company comes out and does it on site, not cheap.
If it is purely cosmetic, with no heavy usage or pressure involved, then I would suggest a good chemi clean down, then stick the parts together with a good 24 hour epoxy (JB Weld or Araldite). Bearing in mind, if you do that, it will never be able to be heat joined afterwards, you will never be able to get all the epoxy out of the grain without copious amounts of work. Cast iron lends itself nicely to this type of repair, as the joints are usually very cleanly broken and fit back together perfectly. As I suggested, a good clean with say cellulose thinners, let it evaporate, spread a nice even coat over both surfaces, getting well into all the nooks and crannies of the break, then assemble and tightly clamp to squeeze all the excess adhesive out, ensuring the edges all match perfectly. Wipe the outside clean, and put to one side for a day for the adhesive to do it's job.
JB weld does a very good job of bonding metal, and I would recommend that over Araldite.
http://cgi.ebay.co.uk/JB-Weld-Industrial-Strength-Adhesive-J-B-Cold-Auto_W0QQitemZ350244192608QQcmdZViewItemQQptZUK_Measuring_Tools_Levels?hash=item518c2e4160&_trksid=p3286.c0.m14A lot of auto accessory shops stock it on their shelves.
Bogs