CNC Ferrous & Non-Ferrous Material Properties 3 — Questions and Answers
Question 1: What is the Brinell Hardness Number (BHN) test most suitable for measuring?
- Thin sheet metal and coatings
- Large castings and forgings with coarse grain structures (Correct answer)
- Ceramic and glass materials
- Hardened tool steel surfaces only
Correct answer: Large castings and forgings with coarse grain structures
The Brinell test uses a large steel or carbide ball indenter and is best suited for large, coarse-grained materials like castings and forgings.
Question 2: Which non-ferrous metal has the highest electrical conductivity among commonly used engineering metals?
- Aluminum
- Copper
- Gold
- Silver (Correct answer)
Correct answer: Silver
Silver has the highest electrical conductivity of all metals, though copper is more commonly used due to cost.
Question 3: When machining copper, the main challenge is:
- Extreme brittleness causing cracking
- High work hardening rate and tendency to form built-up edge (Correct answer)
- Extremely high hardness requiring carbide tooling
- Rapid oxidation that contaminates the cutting fluid
Correct answer: High work hardening rate and tendency to form built-up edge
Copper's high ductility causes it to smear and form built-up edge on cutting tools, requiring sharp tools and appropriate cutting fluids.
Question 4: D2 tool steel is classified as a:
- High-speed steel
- High-carbon, high-chromium cold work tool steel (Correct answer)
- Hot work tool steel
- Shock-resistant tool steel
Correct answer: High-carbon, high-chromium cold work tool steel
D2 is a high-carbon (1.5% C), high-chromium (11-13% Cr) cold work tool steel known for excellent wear resistance.
Question 5: Which stainless steel family is generally non-magnetic and cannot be hardened by heat treatment?
- Martensitic stainless steel
- Ferritic stainless steel
- Austenitic stainless steel (Correct answer)
- Precipitation-hardening stainless steel
Correct answer: Austenitic stainless steel
Austenitic stainless steels (300 series) retain their FCC crystal structure at room temperature, making them non-magnetic and hardenable only by cold working.
Question 6: Which material property is directly measured by a Charpy or Izod impact test?
- Tensile strength
- Hardness
- Toughness (impact energy absorbed) (Correct answer)
- Fatigue limit
Correct answer: Toughness (impact energy absorbed)
Charpy and Izod tests measure the energy absorbed by a notched specimen when struck by a pendulum, quantifying toughness.
Question 7: Magnesium alloys are attractive for aerospace and automotive parts primarily because:
- They are the lightest structural metal in common use (Correct answer)
- They have extremely high melting points
- They offer superior corrosion resistance without treatment
- They are harder than steel
Correct answer: They are the lightest structural metal in common use
Magnesium has a density of about 1.74 g/cm³, making it the lightest structural metal, which is critical for weight-sensitive applications.
CNC Ferrous & Non-Ferrous Material Properties 3
What is the Brinell Hardness Number (BHN) test most suitable for measuring?