Chooses steel, working with key (6)
I believe the answer is:
elects
'chooses' is the definition.
(electing is a kind of choosing)
'steel working with key' is the wordplay.
'working with' indicates anagramming the letters (working with the letters).
'key' becomes 'c' (musical key).
'steel' anagrammed with 'c' gives 'ELECTS'.
(Other definitions for elects that I've seen before include "Selects by a vote" , "Appoints through voting system" , "Votes in" , "Selects by ballot" , "Appoints to position in ballot" .)