My dad has posed an interesting question.

[Spencer Petersen]

When the structure of the spring fails due to corrosion it will break and pieces will fly off due to the tension, releasing any energy contained

Imagine that you are holding a spring in between 2 of your fingers. then it slips out and rockets off, similar to that

 

[Redlin5_v1legacy]

OT: More seriously, the Iron spring would dissolve and the energy would dissipate at the same or faster rate. Kind of boring but true... I think...