AWS Material Selection & Properties 3 — Questions and Answers
Question 1: Which aluminum alloy series is considered non-heat-treatable?
- 2xxx series (copper alloys)
- 6xxx series (magnesium-silicon alloys)
- 7xxx series (zinc alloys)
- 5xxx series (magnesium alloys) (Correct answer)
Correct answer: 5xxx series (magnesium alloys)
The 5xxx series aluminum alloys are strengthened by work hardening rather than heat treatment, making them non-heat-treatable.
Question 2: What is the primary alloying element in 4340 alloy steel?
- Chromium only
- Nickel, chromium, and molybdenum (Correct answer)
- Vanadium and tungsten
- Manganese and silicon
Correct answer: Nickel, chromium, and molybdenum
AISI 4340 is a nickel-chromium-molybdenum alloy steel known for its high strength, toughness, and deep hardenability.
Question 3: In cast iron welding, what makes gray cast iron particularly susceptible to cracking?
- High silicon content reducing fluidity
- Brittle graphite flakes acting as stress concentrators (Correct answer)
- Excessive manganese causing hardness
- Low carbon equivalent reducing weldability
Correct answer: Brittle graphite flakes acting as stress concentrators
Gray cast iron contains graphite in flake form, which acts as stress concentrators and creates brittleness, requiring preheat and slow cooling to prevent cracking.
Question 4: What does ASTM A36 designate in structural steel specification?
- A high-strength low-alloy structural steel
- A common mild structural steel with 36 ksi minimum yield strength (Correct answer)
- A heat-treatable alloy steel plate
- A weathering steel for exposed applications
Correct answer: A common mild structural steel with 36 ksi minimum yield strength
ASTM A36 is a mild carbon structural steel with a minimum yield strength of 36,000 psi (36 ksi), widely used in construction and general fabrication.
Question 5: Which condition describes 'temper embrittlement' in alloy steels?
- Loss of ductility from welding at high interpass temperatures
- Reduced toughness from slow cooling through 375-575°C temperature range (Correct answer)
- Hardening of the HAZ due to rapid quenching
- Softening of the weld metal from excessive heat input
Correct answer: Reduced toughness from slow cooling through 375-575°C temperature range
Temper embrittlement occurs when certain alloy steels are slowly cooled or held in the 375–575°C range, causing impurity segregation to grain boundaries.
Question 6: What is the significance of the 'nil ductility transition temperature' (NDTT) for welded structures?
- Temperature at which the weld pool solidifies
- Temperature below which steel loses its ability to deform plastically before fracture (Correct answer)
- Minimum interpass temperature for low-hydrogen welding
- Temperature at which austenite transforms to ferrite
Correct answer: Temperature below which steel loses its ability to deform plastically before fracture
The NDTT defines the temperature below which a steel transitions from ductile to brittle fracture behavior, critical for structures operating in cold environments.
Question 7: Which copper alloy is classified as a 'red brass' and commonly used in plumbing applications?
- Naval brass (60% Cu, 39% Zn)
- Cartridge brass (70% Cu, 30% Zn)
- 85-5-5-5 (85% Cu, 5% Sn, 5% Pb, 5% Zn) (Correct answer)
- Phosphor bronze (95% Cu, 5% Sn)
Correct answer: 85-5-5-5 (85% Cu, 5% Sn, 5% Pb, 5% Zn)
85-5-5-5 alloy (also called red brass or ounce metal) contains 85% copper with tin, lead, and zinc additions, commonly used for valves and fittings.
AWS Material Selection & Properties 3
Which aluminum alloy series is considered non-heat-treatable?