The Diashield mystery

I'm after a bit of clarity on Seiko's 'super hard' coating – Diashield.

Is it a coating which sits on the surface of the watch? I have heard some say it is heat treatment process which would imply that the material properties of the steel have been changed meaning it is not a coating as such?

Can scratches be polished out or will this remove the coating?

Thank you in advance.