Metallurgy and Phase Diagrams Flashcards

Annealing of a cold-worked metal involves which sequence of microstructural changes?

Answer: Recovery → recrystallization → grain growth

During annealing, recovery occurs first (reducing residual stresses), followed by recrystallization (forming new strain-free grains), then grain growth.

Which type of heat treatment is used to reduce carbon content gradients in cast steel by diffusion at high temperature?

Answer: Homogenization (diffusion) annealing

Homogenization annealing holds the alloy at a high temperature for an extended time to allow diffusion to eliminate compositional segregation from solidification.

In an eutectic binary system, the eutectic point is where:

Answer: A liquid of fixed composition transforms into two distinct solid phases simultaneously

At the eutectic point, a liquid of fixed composition undergoes a simultaneous transformation into two distinct solid phases at a constant temperature.

The solubility of carbon in alpha-ferrite at room temperature is approximately:

Answer: 0.008 wt%

Alpha-ferrite (BCC iron) can dissolve only about 0.008 wt% C at room temperature because its interstitial sites are too small for much carbon.

Precipitation hardening (age hardening) strengthens an alloy by:

Answer: Precipitating fine, coherent second-phase particles that impede dislocation motion

Precipitation hardening produces fine, coherent precipitates dispersed throughout the matrix that act as obstacles to dislocation movement, increasing strength.

What is the primary purpose of case hardening (e.g., carburizing) in steel components?

Answer: To create a hard, wear-resistant surface layer while maintaining a tough core

Case hardening diffuses carbon (or nitrogen) into the surface to enable surface hardening via quenching, producing a hard wear-resistant case over a tough, ductile core.