Claim about splitting iron (7)
I believe the answer is:
profess
'claim' is the definition.
(I know that profess is a more specific form of the action claim)
'about splitting iron' is the wordplay.
'about' becomes 'of' ().
'splitting' indicates putting letters inside (some letters split a word into two).
'iron' becomes 'press' (I've seen this before).
'of' placed into 'press' is 'PROFESS'.
(Other definitions for profess that I've seen before include "Declare openly" , "Affirm faith in (religion)" , "State openly" , "Claim or declare" , "Affirm, acknowledge" .)