Crusher made from steel melted under pressure (6)
I believe the answer is:
pestle
'crusher' is the definition.
(thesaurus)
'steel melted under pressure' is the wordplay.
'melted' indicates an anagram.
'under' means one lot of letters go next to another (below, in a down clue).
'pressure' becomes 'p' (abbreviation).
'steel' with letters rearranged gives 'estle'.
'estle' after 'p' is 'PESTLE'.
'made from' acts as a link.
(Other definitions for pestle that I've seen before include "A grinder or pounder" , "Mortar-grinding tool" , "Tool used in mortar" , "Grinder for mortar" , "Club for grinding" .)