Hey DD & Zulu, I appreciate the compliments.
Welcome to the board, Partsproduction!
Double D has already covered it in two posts, but I'd like to add that those thousands of cast iron cannons that were used through history were also responsible for many deaths and injuries caused to the crews that manned them, and this includes the cast iron cannons used in our Civil War and also beyond that era. John Dahlgren, Robert Parrott, John Brooke and Thomas Rodman are the well-known names of cast iron cannon designers whose models were used in the CW, and they did their best to come up with designs and casting processes that made their guns safer, but every one of these men knew the limitations and dangers involved in using this material to make cannons.
There was a CW field cannon known (among other designations) as a '3-inch ordnance rifle', and it was made using a new wrought iron manufacturing process that resulted in a very strong dependable cannon (only one is known to have burst in service), and it's a well known fact that artillerymen of both the North and South (the CSA captured and used many of these cannons) had high praise for this model; it is also known that a good part of this high regard wasn't concerned with how deadly accurate these guns were against the enemy, but the fact that they felt confident in their own safety when firing them, and I sure can't find any fault with their feelings.
The bottom line to me is that we have modern steels that are undeniably superior to any type of cast iron; so why take an unnecessary chance in firing an unlined iron cannon?