JackD, I hope you didn't get the metal red-hot. Brake line is made from product called Bundy tubing. It's essentially spiral-wound (like your paper towel tube) steel held together with braze. At elevated temperatures you get a phenomenon called Liquid Metal Embrittlement, where the low melting braze attacks the grain boundaries of the steel leading to intergranular fracture. This would be a sudden failure if your brake lines were to let go.

With brake lines the corrosion plus the very soft steel make it nearly impossible to undo using conventional mechanical means. Corrosion is usually strongest at the head/tube interface, not at the threads. I simply cut the line near the head, use a 6-point socket to remove the threaded piece, and replace the line as a unit.

__________________
95 E320 Cabriolet, 169K