Quiz 6

Question 1

Eutectoid Composition

Answer 1

0.75 wt% C. The austenite (y) which exists at high temperatures will decompose (transform) into layers of a and Fe3C, to form a lamellar structure called pearlite.

Question 2

Hypo-eutectoid alloys

Answer 2

0.022wt%-0.76wt% C. The material starts as Austenite and upon cooling the material will be in the two phase region “a+y”. In the case of Fe-C allows the ferrite will form on three grain boundaries. At 727C the austenite disappears and forms two phase a+Fe3C

Question 3

Hyper-eutectoid alloys

Answer 3

> 0.76wt% - 2.14wt%C
The material starts in austenite region. As the material cools we enter the two phase region called y+Fe3C. Similarly as before the Fe3C will precipitate on the grain boundaries. Once we cool below 727C the austenite must disappear, it transforms to a+Fe3C

Question 4

What is on the grain boundaries Ferrite ir Fe3C

Answer 4

Fe3C- hyper-eutectoid
Ferrite(a)- hypo-eutectoid

Question 5

What is the appropriate carbon content of an Fe-C alloy for which the fraction of total ferrite is 0.94?

Answer 5

Co= 0.42 wt%C

Question 6

An alloy has a fraction of proeutectoid ferrite of 0.286 and pearlite of 0.714. What is the concentration of carbon in this alloy. Make sure you correctly identify where a’ is present on the phase diagram.

Answer 6

Co= 0.548wt%

Question 7

Consider we have 2.5 kg of Austenite with 0.65wt% C. This material cooled just below 727C.
a) What is the name of the primary phase
b) How many kg of total ferrite and total cementite will be present below 727C
c) How many kg of pearlite and proeutectoid phase will form

Answer 7

0.38kg