[Metal Materials Function Master Practice] 37th Edition Solution

1. In X-ray inspection, what is the standard used to indicate the quality of the radiograph, which serves as a basis for displaying the sharpness of the taken radiograph, and comes in two types: penetrameter and wire type?
◑ Penetrameter (Image Quality Indicator)

2. Write the names of Bc and Hc in the magnetization curve (x)
◑ Hc: Coercivity

3. The microstructural examination result is shown as DT-Sc-N. Explain this.
※ (1) - (2) - (3) Symbol Explanation
(1) Structure across the entire cross-section
(2) Structure in the center
(3) Other structures

◑ DT: Dendritic structure and pit
◑ Sc: Center segregation
◑ N: Inclusion

4. Convert the following to 100 x 100 mm2: Diameter 25 mm, length 3.6 mm, 5 inclusions (X)

5. Explain (60)x400x0.34% in the nonmetallic inclusion microscopic test.
◐ A: Type of nonmetallic inclusion
◐ 60: Number of fields measured 60
◐ 400: Magnification of microscope 400
◐ 0.34%: Cleanliness 0.34%

6. Write the compositions of duralumin and Y alloy.
◑ Y-Alloy: Al+Cu+Ni+Mg
◑ Duralumin: Al + Cu + Mg

7. Write the method for measuring the thermoelectric power of a thermocouple.
◑ Two different metal wires are welded at one end to create an open circuit. The junction where they are connected is called the measuring junction (hot junction), and the junction where the wires connect to the lead wire or instrument is called the reference junction (cold junction). When a different temperature is applied to the welded part, a thermoelectric power that has a certain relationship with the temperature is generated. Therefore, if the reference junction temperature is kept constant, the temperature of the measuring junction can be determined by this electromotive force. In this case, the metal wire is called a thermocouple.

8. Write the shape memory effect of shape memory materials and the practical excellent alloys.
※ Definition of Shape Memory Alloy
◑ Shape memory alloys are materials that, when manufactured into a product and plastically deformed by external force, return to their original shape when exposed to a certain temperature.
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※ Examples of practical alloys
◑ Ni-Ti based
◑ Cu-Zn-Al based

9. In metallic materials, by dispersing 0.01μ (100nm) fine particles, the deformation resistance of the matrix itself, not the particles themselves, is increased, thereby improving the high-temperature strength and creep characteristics. Write the name and usage (practical material) of this material.
※ Relevant Materials
◐ Dispersion-strengthened metal matrix composite
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※ Practical Materials
◐ SAP
◐ TD Ni

10. Write 5 requirements for electrical steel sheets.
◐ Low iron loss
◐ Low magnetic remanence
◐ Low magnetic aging
◐ High interlaminar resistance
◐ Have appropriate mechanical properties

11. In ultrasonic testing, explain the following terms.
(pulse, gain, time base, ghost echo=reverberation)
◐ Pulse: A signal that lasts for a very short time.
◐ Gain: The degree to which the input voltage of the receiver is amplified. It is evaluated as the ratio of the output voltage to the input voltage of the amplifier.
◐ Time Base: The horizontal axis of the display in the basic display.
◐ Ghost Echo (Reverberation): A phenomenon in which the ultrasonic wave reflects inside the inspection object and returns to the ultrasonic detector, overlapping with the previously generated delayed echo.
◐ Echo: The ultrasonic echo that has been reflected and received.

12. Write the heating temperature and cooling method of the heat treatment that refines the grain structure caused by casting and rolling.
◐ Normalizing (Annealing)
An operation in which steel is heated to a temperature 40-60°C above the Ac3 point or Acm point for a certain period of time to create a fine microstructure, and then slowly cooled in air (air cooling).
◐ The purpose is to refine the grain structure, remove internal stresses caused by cold working, forging, etc., and standardize the mechanical properties, physical properties, and other properties.

13. An Al specimen with a width of 12 mm, thickness of 1 mm, and length of 200 mm has a gauge length of 50 mm marked in the middle. When it stretches to 67 mm, what is the nominal strain in %?

◐ Calculation Formula
Nominal Strain, e = (Change in length / Original length) / Original length
(67/50) / 50 = 0.34

◐ Answer
34%

14. Explain the cooling curve.

① Vapor film stage
◐ The stage where the material is surrounded by the vapor of the cooling liquid, and the cooling rate is slow.

② Boiling stage
◐ The stage where the vapor film is destroyed and boiling occurs, and the cooling rate is fast.

③ Convection stage
◐ The stage where heat is removed by convection, and the temperature difference between the water and the material is small, so the cooling rate is slow.

15. Write about the composition ratio of 7:3 brass.
◐ It is a 70% Cu - 30% Zn alloy and is a representative of working brass. It is widely used to make plates, rods, tubes, and wires.
◐ It is used for automobile radiator parts, sockets, fasteners, various daily necessities, cartridge cases, ornaments, etc.

16. What is the test method that uses the phenomenon of releasing the energy accumulated in the deformed state in the form of elastic waves when a solid is fractured or plastically deformed, and is used for material research, manufacturing management such as welding, and integrity diagnosis of structures?
◐ Acoustic Emission Test (AE)

17. What is the terminology used to distinguish between cold working and hot working, and describe their advantages?
※ Distinguishing Method
◑ Based on the recrystallization temperature of the metal
- Hot working → When working at a temperature higher than the recrystallization temperature
- Cold working → When working at a temperature lower than the recrystallization temperature
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※ Advantages
◑ Hot working