Which materials are ductile and which are brittle?

Typically ductile are structural steels (e.g. S235 with around 26 % elongation), austenitic stainless steels such as 1.4301 (about 45 %), copper and many aluminium alloys. Typically brittle are grey cast iron with lamellar graphite (below 1 %), hardened steels, glass and ceramics. Importantly, ductility is not a fixed material constant – temperature, microstructure, heat treatment and strain hardening can shift the behaviour considerably.