======Annealing and Quenching Bobby Pins======


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**Alternative titles:** Heat Treatment of Steel, Effect of Cooling Rate on Steel Properties
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====Summary====                   
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====Procedure====  
  - Keep one bobby pin as the control (untreated).  
  - Hold a second bobby pin with pliers and heat it in a Bunsen burner flame until it glows red-hot.  
  - Remove it from the flame and allow it to cool slowly in air on a paper towel or fireproof surface, this is annealing.  
  - Hold a third bobby pin with pliers and heat it in the flame until it glows red-hot.  
  - Immediately plunge the hot pin into a cup of cold water to cool it rapidly, this is quenching.  
  - After cooling, test each bobby pin by gently bending it and compare their properties.  




====Links==== 
Heat Treatment of Steel - FlinnScientific: 
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Thermal Processing of Bobby Pins: Interactive Science - Ceramic and Glass Industry Foundation: 
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====Variations====
  * Use oil instead of water for quenching and compare results.  
  * Reheat the quenched pin to moderate temperature and allow it to cool slowly to demonstrate tempering, which increases toughness.  
  * Try using other small steel items such as paper clips or sewing needles.



====Safety Precautions====
  * Wear heat-resistant gloves and safety goggles.  
  * Handle hot metal only with pliers or tongs.  
  * Keep flammable materials away from the flame.  
  * Allow all metal to cool fully before handling.




====Questions to Consider====
  * How does the cooling rate affect the hardness and flexibility of steel?  
  * Why does quenching make the steel hard but brittle?  
  * What happens at the atomic level during annealing compared to quenching?  
  * How does tempering modify the properties of quenched steel?