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Investigating Heat Treatments and Properties of Steel Mark as Favorite (4 Favorites)

LAB in Physical Properties, Heat, Alloys. Last updated May 23, 2022.


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.

For the Student

Objective

You are a material scientist working for a company that makes shocks and struts for car suspension. The company needs to design a steel coil that will be used in the suspension. The ideal coil should have great “memory” and return to its previous shape once it has been compressed. The coil must also be “springy” enough to operate effectively as a shock. Your job is to apply different heat treatments to the steel to determine how to produce the best shock.

Materials

  • Matches or lighter
  • Tongs or forceps
  • Annealed, bare iron 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.

Procedure

1. If it has not been done for you, take the 20-inch piece of wire and cut it into four equal pieces, each about 5-inches long. Using a pencil or pen to wrap the wire around, form each wire piece into a coil/spring. Make sure each wire is the same length with the same number of turns and spacing between the coils. 

2. Control: Test the “springiness” of one of the wires by using your fingers to create compressions. Does it return to its original shape after being compressed once? After several compressions, does it return to its original shape? Record your observations in Table 1: Compressions below. Be specific. (Do NOT simply write “yes” or “no.”) Set this control piece aside for comparison later.

3. Annealing: Take a second wire and heat it to red hot in a Bunsen burner flame, then let it cool slowly to room temperature. Caution: it will be hot. Do not handle it for at least 2 minutes as it cools. Test the “springiness” of this piece in the same manner that you as the control. Record your observations in Table 1: Compressions below and set this piece aside for later comparison.

4. Quenching: Take the third wire and heat it in a burner flame until red hot and then quickly place it in cold water. Be careful to not overheat the coil (don’t keep it in the flame for more than 10 seconds.) Test the “springiness" of this piece of wire just like you did in the previous examples. Record your observations Table 1: Compressions below. Place this piece aside for later comparisons.

5. Tempering: Take the fourth wire and heat it in a burner flame until red hot and then quickly place it in cold water. Dry the wire carefully by dabbing it on a paper towel then heat the wire over a candle/tealight flame for 30 seconds (be sure to move the entire coil in the flame). The metal should show a bluish-colored surface but should not get red hot or overheat the sample and lose the blue coloring. Allow it to cool for at least 2 minutes before handling. Test the “springiness” of this sample as you did in the previous steps. Record your observations in Table 1: Compressions below. Place this piece aside for later comparisons.

6.  Using your fingers, gently pull the ends of each spring to try and straighten them out. Do not overstretch the spring and completely deform it. Which one(s) have the most memory? (This means, which ones “remember” the coiled shape and attempt to remain in that form?) Record your observations in Table 2: Memory.

Data Table 1: Compressions
Spring #
Heat Treatment
Return to original shape after 1 compression?
Return to original shape after several compressions?
1
Control
2
Anneal
3
Quench
4
Temper
Data Table 2: Memory
Spring #
Heat Treatment
Record observations during memory testing of wires:
1
Control
2
Anneal
3
Quench
4
Temper

Analysis

Answer the following questions in complete sentences. Use material science principles to explain your reasoning.

  1. Which sample best returned to its original shape after being compressed several times?
  1. Which sample exhibited the best “memory” and resisted being straightened out?
  1. Which of the coil samples would be the most expensive to produce? Explain.
  1. In your opinion, which sample would make the best coil to be used in the new suspension system of a car? Explain your answer using observations from the experiment. (Note: a suspension system is responsible for making a car ride feel smooth, insulating the passengers from feeling all the bumps on a road).
  1. Explain the effect each heat treatment had on the properties of the steel coil and why these changes occurred.
  1. Producing car parts isn’t the only process that requires different heat treatments to alter the properties of steel. Sword making is another famous process that human civilization has used for centuries. The ACS Reactions video How Do Blacksmiths Make Swords? explains heat treatment used in the sword-making process and how it changed the properties of the steel. Describe the treatments used to create the sword in this video: