Hi Dr G,
En8 will through harden if heated and quenched similar to silver steel and should be okay for filing button use.
With regard to buttons, the hardened type should be held to the part so that they are not moveable – the file skating over as has been stated. This does not affect a file unduly unless very heavy handed though it will wear prematurely
The soft type are best set up to rotate as the file touches them – this will prevent the file rapidly changing their shape!
FWIW I prefer the former as soft buttons are quickly disfigured – just remember to keep both buttons together on a twist of wire once stored – saves a lot of time searching for the matching button!!
Regards – Ramon
Edited By Ramon Wilson on 30/07/2020 22:57:57