I have never heard of any swords being cast other than the bronze swords. But, then, I am not fully informed on all varieties. I would think, however, that casting iron or steel would not make a very strong blade, hard and able to keep an edge, yes, but tough, no. It would be like cast iron, rather brittle, I should think.
The "Sword in the Stone" was, of course, not Excalibur, but just a sword whipped up by Merlin (Myrddin) as a prop to establish Arthur's claim to the throne. It astually has connections to the Sarmatians, a steppe nomadic people, who had sent hostages to Marcus Aurelius after a brutal war. MA had sent them on to serve in Britannia where they continued to serve as heavy cavalry until the Romans witdrew in the period 406 CE to 410 CE. There are some indications that a war leader in the period around 500 CE was using British heavy cavalry in teh Sarmatian/Late Roman mode against the Anglo-Saxon infantry with considerable success, so this person may be the basis for the Arthur legends and, if so, the sword in the stone story would fit.
BTW, Nobody, one more little tidbit on the Dickenson poem is that, when we were all memorizing it for the turkey teacher, one of my classmates was standing on a streetcorner reciting it to himself, oblivious to whoever was around him. All of a sudden, he felt a pat on his shoulder and looked up to see a DC cop who was working a school crossing, patting him on the shoulder and saying, "It's ok, kid. Things will get better!" My classmate came to school in stiches over that one.