[Metal Materials Function Master Practice] 38th Edition Solution

1. Describe the methods for measuring decarburization layer.
◑ Measurement method using a microscope
A method of measuring the depth of the decarburization layer by etching the cross-section of the test piece and observing it under a microscope.

◑ Measurement method using hardness test
A method of measuring the depth of the decarburization layer by conducting a hardness test on the cross-section of the test piece.

2. What is the phenomenon where, at high temperatures, deformation occurs beyond a certain level proportional to the external force over time?
◑ Creep phenomenon

3. Describe the causes of heat treatment hardening failure (hardness failure).
◑ Low quenching temperature
◑ Slow cooling rate
◑ Decarburization and oxidation during quenching

4. Describe two methods for measuring the decarburization layer of heat-treated materials.
◑ Measurement method using a microscope
◑ Measurement method using a hardness test
◑ Measurement method based on carbon concentration

5. Describe the methods for distinguishing between hot working and cold working, and list one advantage of each.
※ Distinguishing method
◑ Based on the metal's recrystallization temperature
-. Hot working → Working at a temperature higher than the recrystallization temperature
-. Cold working → Working at a temperature lower than the recrystallization temperature

※ Advantages
◑ Hot working

※ Countermeasures
◑ Adding alloying elements (Al, Ti, Zr, V, B with high affinity for nitrogen) to prevent temper embrittlement.

11. List three invariant reactions of Fe3C and write their reaction equations (represent liquid as L).
◑ Eutectic reaction: Liquid (4.3%C) → γ Austenite (2.08%C) + Cementite (6.67%C)
◑ Peritectic reaction: Liquid (0.5%C) + α Ferrite (0.09%C) → γ Austenite (0.17%C)
◑ Eutectoid reaction: γ Austenite (0.8%C) → α Ferrite (0.02%C) + Cementite (6.67%C)

12. Describe five general properties of metals.
※ Physical properties
◑ Exists in solid form at room temperature
◑ Has a high melting point and high strength.
◑ Has a specific density and is generally heavy.
◑ Excellent thermal and electrical conductivity.
◑ Requires a lot of processing time, equipment, and cost.

※ Mechanical properties
◑ High hardness and wear resistance.
◑ Good castability and alloy recovery is possible.

13. List five types of fluid flow in leak testing.

※ Influencing factors of the S-curve
◐ Heating rate
◐ Heating temperature
◐ Segregation
◐ Stress
◐ Alloying elements

18. Describe three methods for drawing an S-curve.
※ Methods for obtaining the S-curve
◐ Metallographic method
◐ Thermal analysis method
◐ Thermal expansion method
◐ Magnetic analysis method