1. Tyre wire steels
Tyre wire steels are made into very fine wires,
which are then woven into belts used to give strength to the tread
in vehicle tyres. This kind of steel requires very low levels of
hard non-deformable inclusions (usually high alumina) as these could
cause wire breaks during wire drawing.
Investigate how the occurrence of Al2O3
inclusions affects the wire drawing process. Select an inclusion
level and observe how the wire drawing process is affected.
The fracture surface of a tyre wire break
The fracture surface looks like a 'cup and cone'
fracture and the surface, when viewed in a scanning electron
microscope show its dimpled nature where voids have formed around
the inclusions.
2. Free cutting steels
Free cutting steels are used in the high speed
mass manufacture of complex shaped automotive components (hydraulic
fittings and fasteners - nuts, bolts, screws etc.) in machine lathe
shops. These steels require low levels of hard abrasive inclusions (alumina,
silica) which would otherwise cause premature wear of the cutting
tools. However, manganese sulphide and lead inclusions are
deliberately introduced to this steel type, which act to further
reduce tool wear and promote a good surface finish on the machined
component. See here for purposeful additions for improved
machinability.
3. Pipe plate steels
Pipe plate steels, used in the manufacture of North Sea oil
pipelines require very good toughness to survive extreme service
conditions. Unlike free-cutting steels, very low levels of manganese
sulphide inclusions are required in this steel type. These
inclusions become highly elongated during rolling to give
'stringers'; these stringers act as a plane of weakness in the
finished product, resulting in a piece of this steel having
different physical properties in different directions
(non-isotropy). Stringers also act as 'crack initiators' which can
result in catastrophic failure. The solution to this problem is not
only to provide steels with low levels of manganese sulphide
inclusions but also to modify the shape of the inclusions, i.e. make
them more rounded rather than elongated, by using calcium additions.
