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Heat Treatment of Plain, Low-Carbon Steel
Jessica Henderson & Austin Allen
ENGR45, SRJC 2012
What's in an E45 project:
-Objective -Research -Hypothesis -Process -Problems -Results -Analysis -Conclusion
How would a fire affect the strength of a structure?
?
? ?
?
? ?
Examining heat treated steel
1. Tensile strength 2. Grain size 3. Microstructure 4. Rockwell Hardness test (rb)
Research
What kind of steel is used for structures? What will happen to the tensile strength of steel with heat treatment? How will the heat treatment affect the grain size? What microstructure should we see? How will the hardness relate to the heat treatment?
What we learned from our research:
-Applications of low-carbon steel -No significant difference expected in Yield strength -Grains grow as sample is heated -Larger grains means a softer material
What we expected from our testing: Microstructure:
We expect pearlite and spheroidite, and we know that spheroidite microstructure is the softest
Process
1. Heat Treat 2. Clean and Measure 3. Tensile test 4. Mount, grind, and polish 5. Etch and examine
Heat Treat
1. Mark all samples 2. Austenize all samples at 1400° F to control the
starting microstructure 3. Heat samples I and X at 1250° F to turn pearlite
to spherodite
Clean and measure 1. We used wire brushes to clean off some of the
oxidization layer 2. We needed to clean the threads using a die set and
WD40 3. Be careful not to damage the surface of the samples,
as it would affect the results. 4. We measured length, diameter, and hardness before
testing.
Time to TEST!!! 1. Safety goggles and safety
panel
2. Put the sample in, and turn on the machine.
3. Zero the instruments.
4. Turn up the force!
5. Record data
6. Have an *adult tighten extensometer
Prepare sample for microscope
1. Cut off a lengthwise slice of the specimen. (careful-they get hot!)
2. Mount the samples in bakelite using the specimen mount press.
3. Polish the samples using the grinding/polishing stations
Etch and examine under the digital microscope
1. With our protective equipment donned, we use an ethanol/nitric acid solution to etch the mounted specimens.
2. Using the digital microscope provided at the materials lab, we took pictures of
the microstructure and grain sizes.
Problems
• Samples Austenitized twice after accidental oven use
• Bakelite takes longer to cure than expected
• Needed to rethread our samples after oven use
• Do not unload during tensile strength test
• Jessica ripped her pants
Results
1.Tensile test: confirmed 2.Grain size: confirmed 3.Microstructure: confirmed 4.Hardness: confirmed
Tensile test Our testing supported:
-U.T.S. decreased according to microstructure -Fracture point increased for softer samples
Tensile Strength: As expected
U.T.S. decreased according to microstructure
-Pearlite structure is harder than spheroidite -Our spheroidite samples matched closely
Toughness went down for samples heated longer
Toughness is the area under the curve: as the sample endured longer heat treatment, it lost some toughness.
Fracture point increased for softer samples The spheroidite samples stretched significantly more than the non heat treated specimen.
% Elongation: As expected
Grain size: confirmed
The grain size for the control sample was, on average, smaller than the 1 hour spheroidite sample. The sample that baked for 4 hours had the largest grains.
No heat treatment Austenitized only
1 Hour 4 Hours
Microstructure: confirmed Control sample
Microstructure: confirmed 1 hour spheroidite sample
Microstructure: confirmed 4 hour sample
Hardness: As expected
Our rockwell hardness test supported our tensile graphs, and showed that the pearlite microstructure is harder than either of the spheroidite samples.
Analysis
Overall, our results confirmed our research and hypothesis.
Science did work for us!
Conclusion
How does a fire affect a steel structure?
Our results showed that in every way, heating samples below austenization temp makes them weaker.
Sources:
• Callister, William D., Jr. An Introduction. Ed. David G. Renthwisch. 8th ed. N.p.: n.p., 2010.
Print. • Carbon steel. N.p.: n.p., 2012. Wikipedia. Web. 5
Dec. 2012. <http://en.wikipedia.org/wiki/ Carbon_steel>.