It all depends on what part of the coaster you are talking about. Most of the structure is standard low carbon structural steel, either ASTM A36 or the somewhat stronger versions that I forget the ASTM spec numbers for. In some cases, they may use pipe specification steel for the tubes, but probably not since pipe is more expensive than structural tube. Of course with many of the coasters being built in Europe, the DIN equivalents may be the actual steels used.
