pa1778data.pdf
pa1778data.pdf
pa1778data.pdf
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and is set into the floor of the building.<br />
Installation date: 1943.<br />
HISTORY<br />
U.S. STEEL DUQUESNE WORKS<br />
HAER No. PA-115<br />
(Page 18 6)<br />
The original heat treating plant was installed as part of<br />
the Defense Plant Corporation expansion in 1943. The initial<br />
purpose of the facility was to heat-treat steel bars that were to<br />
be used in the manufacture of guns, shells, and airplane parts.<br />
The plant was expanded in 1962 with the construction of a wing to<br />
the western end of the building containing additional heat<br />
treating equipment. 1<br />
Heat treatment of steel consists of an operation or<br />
combination of operations involving the heating and cooling of<br />
the solid material for the purpose of obtaining desired physical<br />
properties. In heat treating processes, the steel is subjected<br />
to a time-temperature cycle involving two operations — heating<br />
to or above the metal's critical temperature and cooling it to<br />
below its critical temperature. The time involved in the heating<br />
process and the time it takes to cool the steel after it reached<br />
top temperature are crucial determinants in the process of<br />
transforming its physical properties.<br />
The critical temperature is the temperature at which the<br />
crystalline structure of the metal is altered. Heating steel to<br />
above its critical temperature brings it to its so called<br />
austenite or transformation stage, while cooling the metal below<br />
its critical temperature, depending on the method used in<br />
cooling, allows for its physical properties to be permanently<br />
altered in a specific manner. There are three major heat<br />
treating processes—annealing, normalizing, and quench and<br />
tempering. The first two are used to soften steel or make it<br />
more ductile. The last is used to harden and increase the<br />
toughness of steel.<br />
Annealing is a term used to mean any number of treatments<br />
which relieve stresses, and lead to the softening of steel.<br />
These treatments may be divided into two general classes—full<br />
annealing and sub-critical annealing. Full annealing consists of<br />
heating the steel bar above its critical temperature, holding<br />
this temperature for one hour per inch of cross-section, followed<br />
by slow cooling within the furnace through the critical range<br />
until transformation is complete, then ending with air cooling.<br />
In general, the slower the rate of cooling the higher the<br />
temperature at which transformation occurs and the softer the<br />
product. Sub-critical annealing consists of heating the steel<br />
just under the critical temperature, holding at this temperature