Weather affected steel (5)
I believe the answer is:
sleet
'weather' is the definition.
(sleet is a kind of weather)
'affected steel' is the wordplay.
'affected' is an anagram indicator.
'steel' with letters rearranged gives 'SLEET'.
(Other definitions for sleet that I've seen before include "Mixed rain and melting snow" , "unpleasant weather" , "In foul weather" , "Wintry precipitation" , "Partly melted falling snow or hail" .)