For cast iron I use clay-graphite, but they tend to wear rather quickly with temperatures of about 1500 C is my experience. This is interesting: $15 for a decent size crucible (or are it four as the advertises with set of four ?). Even for only one the price is not bad. What do you guys think ? https://www.ebay.com/itm/124681173654?hash=item1d0793ba96:g:ZfwAAOSwqNVf~PjA&LH_BIN=1
It looks like the size and shape of a fire assay cupel used to oxidize the lead from a lead silver mix:
I got this idea from NOBOX7, he said that these fireclay crucibles are rather durable, which I doubt. Probably they are fragile. Admitted, he has some weird ideas. I heard him talking about recovering precious metals from computer waste, like gold, platinum, palladium and Rubidium. The latter is not precious at all, it is an alkali metal like sodium and potassium and it reactivity is even worse than potassium.... And his hunting to iron melting is very inefficient, he uses hundreds of kilowatts, a high pressure oxygen cylinder and and air compressor for melting such a fireclay crucible of 1/4 liter with iron and steel and he does not make 2450 F..... Well if you have the resources (and he has it), get an induction furnace for far less money and costs a lot less energy.
We use fireclay as throwaways for melting scrap Pt and melt sampling (in induction melter). The silica is floating to the top usually as we are at 1800-1880 C and every now and then we have a melt and crack appear but I would imagine these would easily, easily handle cast iron melts, just mind the use of borax: https://dfcceramics.com/index.php?id_product=27&controller=product it would actually be rather trivial for me to melt iron in it. I have melted stainless 316 in these. If anything is their weakness, it's CuO.
