CMS Industrial Materials & Metallurgy 3 — Questions and Answers
Question 1: What is the purpose of the martensite transformation in steel hardening?
- To reduce carbon content
- To produce a hard, body-centered tetragonal microstructure by rapid quenching (Correct answer)
- To eliminate grain boundaries
- To convert iron carbide to graphite
Correct answer: To produce a hard, body-centered tetragonal microstructure by rapid quenching
Rapid quenching traps carbon in the iron lattice, distorting it into a body-centered tetragonal structure called martensite, which is extremely hard and brittle.
Question 2: Which alloying element is added to steel to improve its machinability by forming soft inclusions that act as chip breakers?
- Molybdenum
- Sulfur (Correct answer)
- Tungsten
- Silicon
Correct answer: Sulfur
Sulfur forms manganese sulfide (MnS) inclusions in steel that act as internal lubricants and chip breakers, significantly improving machinability.
Question 3: What is work hardening (strain hardening) in metals?
- Hardening that occurs only at elevated temperatures
- Increase in hardness and strength due to plastic deformation at room temperature (Correct answer)
- Hardening caused by chemical surface treatments
- Hardening from rapid cooling after annealing
Correct answer: Increase in hardness and strength due to plastic deformation at room temperature
Work hardening is the increase in a metal's hardness and yield strength resulting from plastic deformation, which increases dislocation density and impedes further dislocation movement.
Question 4: In the iron-carbon phase diagram, what is the maximum carbon content that defines the boundary between steel and cast iron?
- 0.8% C
- 1.2% C
- 2.14% C (Correct answer)
- 4.3% C
Correct answer: 2.14% C
The boundary between steel and cast iron occurs at 2.14% carbon, which represents the maximum solubility of carbon in austenite at the eutectic temperature.
Question 5: Which surface hardening process introduces nitrogen into the surface layer of steel to increase hardness without quenching?
- Carburizing
- Nitriding (Correct answer)
- Induction hardening
- Flame hardening
Correct answer: Nitriding
Nitriding diffuses nitrogen into the steel surface at temperatures below the critical temperature, forming hard nitride compounds without requiring subsequent quenching.
Question 6: What property describes a material's ability to absorb energy and deform plastically before fracturing, often measured as the area under the stress-strain curve?
- Hardness
- Toughness (Correct answer)
- Elasticity
- Stiffness
Correct answer: Toughness
Toughness is the ability of a material to absorb energy before fracture and is represented by the total area under the engineering stress-strain curve.
Question 7: Which type of corrosion occurs at the contact point between two dissimilar metals in the presence of an electrolyte?
- Crevice corrosion
- Pitting corrosion
- Galvanic corrosion (Correct answer)
- Stress corrosion cracking
Correct answer: Galvanic corrosion
Galvanic corrosion occurs when two dissimilar metals are in electrical contact in an electrolyte, with the more anodic (less noble) metal corroding preferentially.
CMS Industrial Materials & Metallurgy 3
What is the purpose of the martensite transformation in steel hardening?