Procedure: 1. Set aside one bobby pin and one paperclip for comparison. Tape these two on a piece of computer paper and label them “controls”. 2. Heat the loop of a different bobby pin and a loop of a different paperclip red hot and slowly lift out of flame. Slow cool. Tape these two on your paper and label them “Annealed”.
3. Heat the loop of a bobby pin & paper clip each red hot and quench in ice water. Quick cool. Tape these two on your paper and label them “Quenched”.
4. Take one bobby pin & paper clip again and repeat the quenching process from step #3. Next, warm each again in the top of the flame, but only for a few seconds (NOT RED HOT) and then quench. Tape these two on your paper and label them “Tempered”.
5. Bend each paper clip and bobby pin in the same place in the same way. Make sure to do your controls first before the other heated materials. Record your observations of how each paper clip and bobby pin reacts when bent in the data table on the next page. The more detail the better!
6. Clean up all of your materials and return to your seat.
“When you add carbon atoms to iron they tend to be located inside the crystal lattice in places where they fit easily and have relatively little influence on the strength of the iron-carbon alloy known as carbon steel. When you heat carbon steel above a certain temperature a very minor change in its crystal structure happens that has profound consequences. By making a very small shift in position the carbon atoms are relocated to places where they normally wouldn't fit. If only they would stay there then they would prevent the iron atoms from shifting and we would have a much harder material. But if you simply cool the carbon steel fast enough (quenching) and the carbon atoms remain locked in place, you will have a material that is orders of magnitude harder.”
Bobby pins are made of high carbon steel and paper clips are made of low carbon steel.
What kind of defect is this? Explain.
How did the amount of carbon affect the metal’s reactions to the different types of heat treating? (Hint: more carbon made the metal……, less carbon made the metal…..)
What happened to the bobby pin and the paper clips after they were annealed?
(Hint: The number of dislocations were……and the metal was…..)
What happens to metal after being quenched? (Malleability: Ability to change shape without breaking) (Hint: The malleability increased/decreased...because – think about the carbon atoms)