11. Effect of cold working on tensile strength, hardness, ductility and grain size. (The
curve below ductility represents the change in grain size)
12.
13. There is a limit to how much cold work can
be done on a given piece of metal. See the
discussion above about accumulation of
damage in the form of piled up dislocations.
Higher forces are required to produce a
given deformation, which means we need
heavily built, strong forming machines .
14. HOT WORKING
• Hot working refers to the process where
metals are defromed above their
recrystallizatıon tempereture and strain
hardening does not occur.Hot working
performed at elevated tempreature.However
is hot working at room temperature because
of its low melting temperature.
21. The advantages of hot
working
Sometimes hot working can be combined with a casting process so that metal
is cast and then immediately hot worked. This saves money because we don't
have to pay for the energy to reheat the metal.
Hot working tends to break up large crystals in the metal and can produce a
favourable alignment of elongated crystals
Hot working can remove some kinds of defects that occur in cast metals. It can
close gas pockets (bubbles) or voids in a cast billet; and it may also break up
non-metallic slag which can sometimes get caught in the melt (inclusions).
23. The Disadvantages of hot working
There is the constant
annoying problem of scale
formation on the surface of
the hot steel.
There is a lot of
dimensional change as
the worked object cools