Summary

In this lab, students will take on the perspective of a material scientist working for a company that makes shocks and struts for car suspension by applying three different heat treatments to steel coils. Students will test how these heat treatments affect the properties of the high carbon steel.

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• HS-PS2-5: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
• Scientific and Engineering Practices:
• Analyzing and Interpreting Data
• Planning and Carrying Out Investigations

Objectives

By the end of this lab, students should be able to:

• Describe how different heat treatments affect steel at the atomic level.
• Explain how heat treatments alter the properties of steel.

Chemistry Topics

This lab supports students’ understanding of:

• Physical Properties
• Heat Treatments
• Alloys
• Metallic Properties

Time

Teacher Preparation: 30 minutes
Lesson: 60 minutes (30 minutes for lab and 30 minutes for discussion)

Materials

• Needle nose pliers or scissors (to cut the iron wire)
• Matches or lighter

For each lab group:

• Tongs or forceps
• Annealed, bare iron wire
• Wire can be purchased at home depot/hardware store or Amazon. 
• Avoid wire that has any plastic coating or films.
• Each group needs about 20 inches of wire, cut into 4 equal lengths (~5 inches each).
• Tea light candle
• 100 mL or 250 mL beaker
• Pencil or glass stirring rod
• Ruler
• Bunsen burner
• Water

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
• An operational fire extinguisher should be in the classroom.

Teacher Notes

• Students can work in groups of 2–3 at a lab station for this activity.
• Emphasize and demonstrate safe handling of the metal samples using tongs or forceps so students do not burn themselves.
• Prior to starting this activity, students should be familiar with the following:
  • Definition of an alloy. This can be done by completing a pre-lab discussion with the students. The definition I use with my general science students is: an alloy is a mixture of two types of metals.
  • Understand that steel is an interstitial alloy between iron and carbon atoms. This can be done with a pre-lab discussion with the students. I use this definition with my students: an interstitial alloy is made when smaller atoms fit in between the spaces (or interstices) of larger atoms. It is also good to note that steel is an alloy made between a metal (iron) and a nonmetal (carbon).
• It is helpful if the teacher precuts a 20-inch piece of iron wire to give to each group. These can then be cut again into four equal 5-inch pieces by the teacher or students.
• Each group should first prepare the 4 wire samples by wrapping each wire around a pencil or glass stirring rod to create 4 coils that are the same.
• Remind students that it is important to make the coils as uniform as possible.
• It is also helpful to demonstrate the preparation of each sample and the heat treatment for each step:
  • Control: The 5” piece of iron wire is wrapped around a pencil to create a coil. No heat treatments are applied. Be sure students place the control coil on a labeled sheet of paper so they remember which one it is.
  • Anneal: Hold a 5” iron coil with tongs in a burner flame until red hot. Allow it to cool on the lab counter for 2 minutes before touching.
  • Quench: Hold a 5” iron coil with tongs in a burner flame until red hot, then quickly plunge it into cold water.
  • Temper: Hold a 5” iron coil with tongs in a burner flame until red hot, then quickly plunge it into cold water. Dry the coil with a paper towel. Heat the coil over a candle flame for 30 seconds moving the entire coil in the flame and then allow it to cool on the lab bench for 2 minutes before handling.
• When testing compression:
  • Instruct students to do so gently and be reminded to not smash the coil.
  • It’s helpful if students hold the coil between their index finger and thumb and qualitatively note how the coil feels as it is compressed. I direct them to pay attention to how well the coil rebounds, how soft it feels, etc.
• When testing memory:
  • Instruct students to pull the coil gently so it doesn’t completely pull apart.
  • Students can hold the coil between their fingers and note qualitatively how the coil responds as it is pulled apart. I direct them to pay attention to how “springy” it feels.
• After students have completed the lab and answered the questions as best as possible, I go over the answers with them to ensure they understand the concepts.
• The last analysis question in the student handout requires students to watch the ACS Reactions video (5 minutes, 30 seconds), How Do Blacksmiths Make Swords? It explains the heat treatment used in the sword-making process along with how it changed the properties of the steel.
• This activity fits in well with chemical and physical properties or types of chemical bonding.
• After the lab, you can extend the learning by having students read the December 2005 ChemMatters article, Secrets of the Samurai Sword Revealed. You can read it as a class and discuss it or assign it as homework as an extension. This article describes many of the heat treatments employed in this lab and explains how they are used in producing a sword.