2. Properties in general:
Ductility : ability to be drawn into wire without fracture.
Malleability : ability to be rolled / beaten into sheets without fracture.
Tensile strength : maximum load that it can support without yielding.
Elastic deformation : deformation to an extent that the original shape can be
regained when the applied load is removed.(pulling a rubber band)
Plastic deformation: deformation that is permanent. Pressing clay.
3. Types of steel
(Based on C content)
low carbon
medium carbon
high carbon
4. Low carbon steel
Low carbon steels generally contain less
than 0.25% Carbon :
It is relatively soft and weak,
Has good ductility and toughness
It is machinable,(because it is soft and
not brittle)
Weldable
Relatively inexpensive to produce.
5. Medium carbon steel
Medium carbon steels have carbon
concentrations between about 0.25 and
0.60 wt.
These steels may be heat treated by
heat to improve their mechanical
properties.
Good load carrying ability (Because it
has the best blend of ductility and
toughness)
6. High carbon steel
High carbon steel have carbon content
around 0.30–1.70
Cannot be welded.
Cannot be machined (too hard and
brittle)
Production cost increases because of
hardness.
7. What is an alloy steel :
Carbon steel can be classified as an alloy
steel when
The manganese content exceeds 1.65%,
Or, when silicon /copper exceeds 0.60%
Change in composition results in change in
ductility and its reaction to heat treatment. So
by heat treatment we can increase the
strength to desired level and get different
blends of ductility and strength.
8. What is stainless steel:
Stainless steel has at least 10.5%
Chromium. That accounts for its
corrosion resistance.
Nickel or molybdenum are added to
increase strength and heat resistance.
9. Crystal Grains
• All steels are made of building blocks called grains.
Mechanical properties depend upon the composition and grains shape and size.
• Generally heat treatments don’t change composition unless we generate
special environment for that {like for removal of carbon from steel})
Grain
Grain boundary
10. Treatments :
Heat treatment affects the grain size .
Effects of annealing : (heating and then slowly cooling)
Annealing is used to induce ductility.
Soften the material( in case of low carbon steel)
Increase hardness and strength(in case of high carbon
steel)
Cold rolling (below recrystallsation temperature) can be done
for :
hardening or,
for fabricating a shape out of a given sheet.
