Beth,
Corten is supposed to weather very evenly, I'm thinking a good choice for an exterior project, near salt water. My community needs the entrance to our cemetery completed, possibly with an arch. I'm hesitant to use mild steel because with the high percentage of carbon nowadays, it weathers so badly. I'm considering stainless steel or silicon bronze boat shafts, though I really don't know much about those materials either...
JIm