ME Metals and Alloys 2 — Questions and Answers
Question 1: Austenitic stainless steels (e.g., 304) are non-magnetic primarily because:
- They contain no iron
- The FCC austenite phase is paramagnetic (Correct answer)
- They have very high carbon content
- They are cold-worked
Correct answer: The FCC austenite phase is paramagnetic
Austenitic stainless steels retain the FCC austenite phase at room temperature due to high nickel content, and this phase is paramagnetic (non-magnetic).
Question 2: The tempering of martensite in steel is performed to:
- Increase hardness and brittleness
- Improve toughness by relieving internal stresses and precipitating carbides (Correct answer)
- Dissolve carbon into solid solution
- Convert pearlite to martensite
Correct answer: Improve toughness by relieving internal stresses and precipitating carbides
Tempering heats quenched martensite to an intermediate temperature, allowing carbon to precipitate as fine carbides and relieving residual stresses, improving toughness.
Question 3: Which copper alloy is known for its excellent spring-back properties and electrical conductivity?
- Bronze (Cu-Sn)
- Brass (Cu-Zn)
- Beryllium copper (Cu-Be) (Correct answer)
- Monel (Ni-Cu)
Correct answer: Beryllium copper (Cu-Be)
Beryllium copper has the highest strength and hardness of any copper alloy, combined with excellent spring properties, making it ideal for electrical connectors and springs.
Question 4: The Jominy end-quench test is used to measure which property of steel?
- Fracture toughness
- Hardenability (Correct answer)
- Creep resistance
- Impact toughness
Correct answer: Hardenability
The Jominy end-quench test measures hardenability by quenching one end of a bar and measuring hardness as a function of distance from the quenched end.
Question 5: Grain refinement in metals typically results in:
- Decreased yield strength
- Increased yield strength and toughness (Correct answer)
- Increased ductile-to-brittle transition temperature
- Decreased hardness
Correct answer: Increased yield strength and toughness
According to the Hall-Petch relationship, smaller grain size increases yield strength, and fine-grained metals also generally show improved toughness.
Question 6: Which heat treatment process produces a spheroidized microstructure in steel to improve machinability?
- Normalizing
- Full annealing
- Spheroidize annealing (Correct answer)
- Stress relief annealing
Correct answer: Spheroidize annealing
Spheroidize annealing involves extended heating near the eutectoid temperature, causing cementite to assume a spheroidal morphology, which maximizes machinability and ductility.
ME Metals and Alloys 2
Austenitic stainless steels (e.g., 304) are non-magnetic primarily because: