©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART A 1.5.6
Normalizing
- The main difference between normalizing and annealing is the
method of cooling. Normalized
steel is heated to a temperature approximately 100° above
where the microstructure transforms
and then cooled in still air rather than in a furnace. 1.5.7
Heat
Treatment Trade-Off - It must be noted that these
various ways of control- ling
the heating and cooling of metals can produce a desired property, but sometimes
at the expense
of another desirable property. An example of this trade-off is evident in
the fact that
certain heat treatments can increase the strength or hardness of metal, but the
same treatments
will also make the metal less ductile or more brittle, and therefore, susceptible
to welding problems.
1.6 PROPERTIES
OF METALS The
usefulness of a particular metal is determined by the climate and conditions in
which it will
be used. A metal that is stamped into an automobile fender must be softer
and more pliable
than armor plate that must withstand an explosive force, or the material used
for an oil rig
on the Alaska North Slope must perform in a quite different climate than
a steam boiler.
It becomes obvious that before a material is recommended for a specific
use, the physical
and mechanical properties of that metal and the weld metal designed to join it
must be evaluated. Some of the
more important properties of metals and the means of evaluation
are as follows: 1.6.1
Tensile
Strength - Tensile strength is one of the most
important determining factors
in selecting a metal, especially if it is to be a structural member, part of a
machine, or part
of a pressure vessel. 1.6.1.1
The tensile test is performed as shown
in Figure 4. The test specimen is machined
to exact standard dimensions and clamped into the testing apparatus at both
ends. The specimen is then
pulled to the point of fracture
and the data recorded.
1.6.1.2 The
tensile strength test
gives us 4 primary pieces of
information: (1) Yield Strength,
(2) Ultimate Tensile Strength,
(3) Elongation, and (4) Reduction
in Area. FIGURE
4 RECORDING
DIAL TEST
SPECIMEN FORCE
TENSILE TESTING APPARATUS
