Firm that's manufactured our steel (8)
I believe the answer is:
resolute
'firm' is the definition.
('resolute' can be similar in meaning to 'firm')
'manufactured our steel' is the wordplay.
'manufactured' is an anagram indicator.
'our'+'steel'='oursteel'
'oursteel' anagrammed gives 'RESOLUTE'.
'that's' is the link.
(Other definitions for resolute that I've seen before include "without flinching" , "'Firm, unhesitating (8)'" , "Admirably purposeful" , "Firm-minded" , "'Determined, dead set on (8)'" .)