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?

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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>.