1. In X-ray inspection, what is the criterion used to indicate the clarity of the radiographic image taken, which is a measure of the image quality? There are two types: radiographic density and steel core type.
◑ Penetrameter (Image Quality Indicator)

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

3. The microstructural examination results were indicated as DT-Sc-N. Explain this.
※ Explanation of symbols (1) - (2) - (3)
(1) Tissue that spans the entire cross section
(2) Tissue in the central part
(3) Other tissue

◑ DT : Dendritic structure and pits
◑ Sc : Central segregation
◑ N : Inclusion

4. Convert 25mm in diameter, 3.6mm in length, 5 inclusions to 100 x 100mm2 (X)

5. Explain (60)x400x0.34% in the non-metallic inclusion microscopic test
◐ A : Type of non-metallic inclusion
◐ 60 : Number of measurement fields 60
◐ 400 : Microscope magnification 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 of measuring the thermoelectric power of a thermocouple.
◑ When two different metal wires are welded together at one end to create an open circuit, the junction where the wires are connected is called the hot junction (measuring junction) and the junction where the wires are connected to the leads or instruments is called the reference junction (cold junction). When a different temperature is applied to the welded portion, a thermoelectric power that has a fixed 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 excellent alloys used for it.
※ Definition of shape memory alloy
◑ A shape memory alloy is a material that is shaped into a product and then subjected to plastic deformation by external force. When it is exposed to a certain temperature, it returns to its undeformed state.
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※ Examples of practical alloys
◑ Ni-Ti system
◑ Cu-Zn-Al system

9. In metallic materials, what is the name of the material in which 0.01μ (100nm) fine particles are dispersed, thereby increasing the deformation resistance of the matrix itself, not the particles themselves, to improve high temperature strength and creep characteristics? Write the name and application (practical material).
※ Material that corresponds to this
◐ Dispersion-strengthened metal composite material
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※ Practical materials
◐ SAP
◐ TD Ni

10. Write the 5 requirements for electrical steel.
◐ Iron loss should be low
◐ Anisotropy should be low
◐ Magnetic aging should be low
◐ Interlayer resistance should be high
◐ Have appropriate mechanical properties

11. Explain the following terms in ultrasonic testing
(pulse, gain, time axis, ghost echo=reverberation reflector)
◐ Pulse : A signal that lasts for a very short time.
◐ Gain : The degree to which the input voltage of the receiver is amplified, evaluated as the ratio of the output voltage to the input voltage of the amplifier.
◐ Time axis : The horizontal axis of the display in the basic display.
◐ Reverberation echo (ghost echo) : When the ultrasonic wave is reflected inside the test object and returns to the ultrasonic detector, it overlaps with the previously generated delayed echo, resulting in this phenomenon.
◐ Echo : Reflected ultrasonic echo received.

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

13. A 12mm wide, 1mm thick, 200mm long Al specimen was marked with a 50mm gauge length in the middle. When it was stretched to 67mm, what is the nominal strain in %?

◐ Calculation formula
Nominal strain, e = (Change in length / Initial length) / Initial length
(67/50) / 50 = 0.34

◐ Answer
34%

14. Explain the cooling curve.

① Vapor film stage
◐ The stage where the material is enveloped by the vapor of the cooling liquid, resulting in a slow cooling rate.

② Boiling stage
◐ The vapor film is destroyed and boiling occurs, resulting in a fast cooling rate.

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

15. Write about the composition of 7:3 brass.
◐ It is a 70% Cu - 30% Zn alloy, representing a typical brass for processing, and 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 used for research on materials, manufacturing management such as welding, and suitability diagnosis of structures, by detecting the energy stored in the deformed state as elastic waves when a solid is broken or plastically deformed?
◐ Acoustic Emission (AE) test

17. What is the term used to distinguish between cold working and hot working, and describe their advantages?
※ Method of distinction
◑ Based on the recrystallization temperature of the metal
-. Hot working → When the metal is worked at a temperature above the recrystallization temperature.
-. Cold working → When the metal is worked at a temperature below the recrystallization temperature.
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※ Advantages
◑ Hot working