The crossword solution for the term 'Toughens, as metal' is 'Anneals'. Annealing is a heat treatment process used to alter the physical and sometimes chemical properties of a material. It is often used to soften metals such as steel and to make them more workable. The process involves heating the metal to a specific temperature and then allowing it to cool slowly. This process causes the metal to become more ductile and less brittle, making it easier to shape and form.