18. Phase Diagrams III Fe-C System

Question 1

What wt% C is pure cementite (Fe3C) formed at?

Answer 1

6.70%

Question 2

What is the 𝛼 phase called?

Answer 2

Ferrite

Question 3

What is the 𝛾 phase called?

Answer 3

Austentite

Question 4

What is the symbol for the ferrite phase?

Answer 4

𝛼

Question 5

What is the symbol for the Austentite phase?

Answer 5

𝛾

Question 6

When a liquid at the eutectic composition of iron and carbon is cooled below the eutectic point what is the substance formed?

Answer 6

Pearlite (a lamellar microstructure)

Question 7

Is ferrite brittle or ductile?

Answer 7

Ductile

Question 8

Is cementite brittle or ductile?

Answer 8

brittle

Question 9

How do you find the weight fraction of pearlite in the 𝛼 + Fe3C region at a non-eutectic composition?

Answer 9

Draw a tie line just above the eutectic isotherm to determine the weight fraction of 𝛾. The 𝛾 present here will all become pearlite.

Question 10

The prefix hypo means _____

hypo-eutectic

Answer 10

before

ie before the eutectic composition

Question 11

The prefix hyper means ____

hyper-eutectic

Answer 11

after

ie after the eutectic composition

Question 12

The strength of Pearlite increases with _____ interlaminar spacing, S

Answer 12

decreasing

Question 13

Fine pearlite is ____ (weaker/stronger) than coarse pearlite

Answer 13

stronger

Question 14

Why is fine pearlite stronger than coarse pearlite

Answer 14

finer = more grain boundaries = dislocation movement more inhibited = less chance of slip = stronger