This video based module documents a set of experiments which were developed at the University of Pennsylvania by Dr. Charles McMahon. The experiments demonstrate the effects of heat treating 1040 steel with quenching performed by air, oil, water, and in the furnace. Effects are analyzed by Rockwell hardness testing and examination of the steel's microstructure.


Four specimens of 1040 steel are placed into a box-type furnace set at 850 C. This temperature is used since it is appropriate for austenizing this steel. The specimens are placed into a graphite box in the furnace to cut down on oxidation and decarburization.
After being held at temperature for 30 minutes, three of the specimens are removed for cooling. The first is water quenched (as shown). This is the fastest cooling rate used and will convert the outer part of the specimen to martensite. Two other specimens are oil cooled and air cooled. The remaining specimen is furnace cooled. This is done by covering the graphite box with a graphite cover and switching off the furnace.
Once the specimens are cooled, they are polished. This is performed in a series of steps using a rotating disc grinder. Initially, sandpaper of decreasing grit is used with the orientation of the specimen changing by roughly 90 degrees with each change in paper. The paper is changed once the scratches made by the preceeding grit are completely replaced by those formed by the current grit. After the lowest grit of sandpaper is used, the process is continued in the same way using polishing compound.
This is a polished specimen.
A testing machine is used to find the Rockwell hardness of the specimens. The testing machine has several parts: a heavy steel frame with a specimen stage that can be raised and lowered, an indenter connected by levers to a weight pan at the rear of the frame, and a dial that records the depth of the indention of the specimen. The dial has several scales that correspond to different combinations of load and indenter, and each of these combinations corresponds to a particular Rockwell hardness scale.
The machine is verified to be properly operating by testing it on a calibration block. It is then used to test the hardness of the samples. At least three readings are taken for each specimen and the average of these is recorded as the hardness. An indented specimen is shown here.
Finally, metallographic samples are examined to reveal how the heat treatments affect the resulting microstructure. In this picture, the microstructure of the furnace cooled steel is shown at a magnification of 1000X. The proeutectoid ferrite formed as the first part of the decomposition of austenite as it cooled from 850 C. It began at the grain boundaries of the austenite and grew out, rejecting carbon into the austenite as it did. Pearlite formed later from the remaining austenite, which by then had reached a carbon content of about 0.8%.


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