Fundamentals of Engineering Materials Science 2

Question 1

On the iron-carbon phase diagram, the eutectoid composition is approximately:

Accepted Answer

0.76 wt% C

Answer

The eutectoid point occurs at 0.76 wt% C and 727°C, where austenite transforms isothermally to pearlite (ferrite + cementite).

Question 2

Martensite in steel is formed by:

Accepted Answer

Rapid quenching of austenite

Answer

Rapid quenching of austenite traps carbon in a supersaturated body-centered tetragonal structure, producing hard, brittle martensite through a diffusionless transformation.

Question 3

Which heat treatment reduces brittleness of quenched (martensitic) steel by heating below the eutectoid temperature?

Accepted Answer

Tempering

Answer

Tempering reheats martensitic steel to a sub-eutectoid temperature, allowing some carbon precipitation and relieving internal stresses to improve toughness.

Question 4

The lever rule in a two-phase region of a phase diagram is used to determine:

Accepted Answer

The relative weight fractions of each phase present

Answer

The lever rule uses the tie line in a two-phase region to calculate the weight fraction of each phase present at a given overall composition and temperature.

Question 5

Precipitation hardening (age hardening) increases strength by:

Accepted Answer

Generating fine precipitates throughout the matrix that obstruct dislocation motion

Answer

Fine, coherent precipitates act as obstacles that dislocations must either cut through or bypass (Orowan looping), both requiring additional stress.

Fundamentals of Engineering Practice Test

Fundamentals of Engineering Practice Test

Fundamentals of Engineering Materials Science 2