As designers, we ideally want the DBTT to be as low as possible for low-temperature design. Metals such as aluminum, gold, silver, and copper have an FCC (face-centred cubic) crystal lattice structure, and most do not experience a shift from ductile to brittle behaviour. Other metals, such as iron, many steels, chromium, and tungsten, have a BCC (body-centred cubic) crystal structure and experience a sharp, often non-linear shift in ductility. Note that austenitic stainless steels, such as SAE 200- and 300-series (e.g. 316 stainless), have an FCC structure and do not experience a ductile-brittle transition. On the other hand, ferritic and martensitic stainless steels, such as SAE 400-series (e.g. 416 stainless), have a BCC structure and do experience a ductile-brittle transition.