Steels having high hardenability are required to make large high-strength compo-
nents, such as large extruder screws for injection moulding of polymers, pistons for
rock breakers, mine-shaft supports, aircraft undercarriages, as well as small, high-
precision components, such as die-casting moulds, drills and presses for stamping
coins. The slower cooling rates that can be used for high hardenable steels can reduce
thermal stresses and distortion. Steels having low hardenability may be used for
smaller components, such as chisels and shears, or for surface-hardened components,
such as gears, where there is a desire to maintain a ferrite/pearlite microstructure at the
core to improve toughness.