Nickel-titanium ("nitinol") shape-memory alloys are also "superelastic", which means they have an additional range of deformation past normal elastic deformatio

Nickel-titanium ("nitinol") shape-memory alloys are also "superelastic", which means they have an additional range of deformation past normal elastic deformation before plastic deformation from which they return back to their original shape. So, not just spring steel.