[Metal Materials Functional Master Practical] 36th Edition Solution

1. Describe the HRC 6066, STB2 distortion prevention heat treatment cycle.
※ HRC 6066, STB2 (High Carbon Chromium Steel)
◑ Q(quenching)-T(tempering) after Soaking treatment
◑ Maintain around 700 degrees below the quenching temperature for about 3 hours, then air cool.
◑ 790-820 degrees for 30 minutes, 25 minutes air cool, then air cool at Ms(170-130).
◑ 150-180 degrees for 40 minutes, 25 minutes, then water cool.

2. Chloride salt bath was selected to obtain an upper bainite microstructure for a high-speed engine shaft sensitive to distortion. Write down 3 components of a low-temperature salt bath. (Melting Point: 2360 degrees, Operating Temperature: 400 degrees)
◑ Low-temperature salt bath: Sodium Nitrate, Potassium Nitrate, Sodium Nitrite, Potassium Nitrite

3. List the methods for obtaining the S-curve. (3 methods for obtaining the CCT curve)
◐ Metallurgical method
◐ Thermal analysis method
◐ Thermal expansion method
◐ Magnetic analysis method

4. Find the degree of freedom using the phase rule at the eutectic point.
◐ F=C+1-P
◐ C = 2 , P = 3 , F = 0

5. Using a 120-degree diamond cone with a 150kg load for Rockwell hardness test, what is the HRC when the depth of the indentation is 0.045mm?
◐ Calculation formula
HRC = 100 - 500h (h = indentation depth in mm)
100 - 500 x 0.045 = 77.5

◐ Answer
77.5

6. Define fatigue limit and explain how the fatigue limit is determined for metals like Al where it is difficult to determine.
※ Fatigue Limit Definition
◑ The maximum stress value that does not cause permanent failure of a material even when subjected to repeated loading.

※ When it is difficult to determine the fatigue limit for aluminum (Al)
◑ The stress amplitude at 10 to the power of 7 cycles is defined as the fatigue limit (determines the effective life of a product or component).

7. If a carburizing treatment was performed for 7 hours, including diffusion time, using a 0.25% C carburizing steel with a target carbon concentration of 0.8% and resulted in a surface carbon concentration of 1.15%, what is the carburizing time?
◑ Harris's equation
Tc = Carburizing time required, Tt = Carburizing time + Diffusion time
C = Target surface carbon concentration (%), Co = Carbon concentration during carburizing (%), Ci = Carbon concentration of the base material (%)

◑ Calculation formula
Tc = Tt ((C - Ci) / (Co - Ci))2
Tc = 7 * ((0.8-0.25)/(1.15-0.25))2

◑ Answer
Tc = 2.6 hours

8. In the Fe-C phase diagram, the carbon content is 4.3% (①) point, the degree of freedom at the eutectic point is (②), the magnetic transformation temperature is (③) degrees, and the cubic lattice (④) of γ-iron and α-iron.
◑ ① : Eutectic point
◑ ② : 0
◑ ③ : A2 (768 degrees)
◑ ④ : BCC

9. Describe what the mass effect is.
◑ Even for the same steel, the hardening depth differs depending on the size, thickness, and mass shape of the product.

10. Explain hardenability.
◑ Even for products of the same size, the hardening depth during quenching differs depending on the type of steel. The property of the steel itself that governs this hardening depth is called hardenability.

11. Distinguish between linear magnetization and circular magnetization by magnetization method in magnetic particle inspection.
※ Linear Magnetization Method
◑ Yoke method (M)
◑ Coil method (C)

※ Circular Magnetization Method
◑ Central conductor method (I)
◑ Head shot method (EA)
◑ Prod method (P)

12. Connect the related items to the thermocouple (Explain about the thermocouple_alternative).
※ Thermocouple Requirements (Heat & Internal heat resistance)
◑ High thermoelectric power
◑ Able to withstand high temperatures
◑ High heat resistance
◑ High corrosion resistance
◑ Low thermal conductivity

13. Write down 3 purposes of cryogenic treatment for bearing steel, precision machine steel, and gauge steel.
◑ Dimensional change prevention
◑ Aging distortion prevention
◑ Strengthen the steel
◑ Strengthen the carburized layer
◑ Improve the mechanical properties of stainless steel
◑ Transform residual austenite to martensite

14. Explain the lamination inspection method.
※ Lamination
Internal defects in rolled steel, such as non-metallic inclusions, that are aligned parallel to the rolling direction, resulting in a layered structure.

15. Describe 5 conditions and precautions for general heat treatment tooling materials.
◑ Good heat resistance
◑ Very low high-temperature deformation
◑ Easy to manufacture
◑ Corrosion-resistant material
◑ Maintain sufficient hardness against deformation

16. Write down 4 advantages and 3 disadvantages of eddy current testing.
※ Advantages (High speed & non-contact & inspection)
◑ Inspection is possible even at high temperatures.
◑ Non-contact and fast inspection speed.
◑ Inspection records can be stored.
◑ Excellent surface defect detection capability.

※ Disadvantages (Internal defect inspection)
◑ Not suitable for internal defect measurement.
◑ Difficult to inspect complex shapes.
◑ It is difficult to directly determine the type and shape of defects from the indications obtained from the inspection.

17. Explain the mass effect during heat treatment.
◑ Mass effect
The hardening depth differs depending on the size, dimensions, and thickness of the material, even for the same steel.
Judging the heat treatment effect based on the size and shape of the material.