With minimum information in , one gets minimum information out. Corten is relatively high strength steel , with 50,000 + psi yield compared to 35,000 psi yield for ordinary hot rolled steel.It is intended for atmospheric exposure ( occasional wet , usually dry) , not buried or in a location where it is always wet. Steels are about 4 X heavier than concrete in density.
I had to search this item. When you fill one of the planters shown on the net with soil , it will hold back a slope. No add say how thick the steel is , so I guess about 0.030", that could last 10 to 20 years before rusting out from the inside wet surface. Rust from the outside will leave brown stains on anything like a concrete patio ; the rust would disappear on a grass surface. Of no significance, many are not likely Cor-Ten , a copyright name of USX.