pa1778data.pdf

and is set into the floor of the building.
Installation date: 1943.
HISTORY
U.S. STEEL DUQUESNE WORKS
HAER No. PA-115
(Page 18 6)
The original heat treating plant was installed as part of
the Defense Plant Corporation expansion in 1943. The initial
purpose of the facility was to heat-treat steel bars that were to
be used in the manufacture of guns, shells, and airplane parts.
The plant was expanded in 1962 with the construction of a wing to
the western end of the building containing additional heat
treating equipment. 1
Heat treatment of steel consists of an operation or
combination of operations involving the heating and cooling of
the solid material for the purpose of obtaining desired physical
properties. In heat treating processes, the steel is subjected
to a time-temperature cycle involving two operations — heating
to or above the metal's critical temperature and cooling it to
below its critical temperature. The time involved in the heating
process and the time it takes to cool the steel after it reached
top temperature are crucial determinants in the process of
transforming its physical properties.
The critical temperature is the temperature at which the
crystalline structure of the metal is altered. Heating steel to
above its critical temperature brings it to its so called
austenite or transformation stage, while cooling the metal below
its critical temperature, depending on the method used in
cooling, allows for its physical properties to be permanently
altered in a specific manner. There are three major heat
treating processes—annealing, normalizing, and quench and
tempering. The first two are used to soften steel or make it
more ductile. The last is used to harden and increase the
toughness of steel.
Annealing is a term used to mean any number of treatments
which relieve stresses, and lead to the softening of steel.
These treatments may be divided into two general classes—full
annealing and sub-critical annealing. Full annealing consists of
heating the steel bar above its critical temperature, holding
this temperature for one hour per inch of cross-section, followed
by slow cooling within the furnace through the critical range
until transformation is complete, then ending with air cooling.
In general, the slower the rate of cooling the higher the
temperature at which transformation occurs and the softer the
product. Sub-critical annealing consists of heating the steel
just under the critical temperature, holding at this temperature