Chapter 13- Isothermal Transformation Diagrams

Question 1

What is the purpose of isothermal diagram?

Answer 1

It provides the different steel structures that are transformed from austenite over a period of cooling time.

Question 2

What are the other two names for an I-T diagram?

Answer 2

I-T diagrams are commonly called time-temperature-transformation (T-T-T) diagrams. They are also called C curves or S curves.

Question 3

What valuable piece of information does the iron-carbon phase diagram lack?

Answer 3

It does not indicate the amount of time involved in the cooling process. Does not differentiate between slow and rapid cooling rates in terms of time so there is no way to know the cooling process or the type of steel structure that is produced.

Question 4

In addition to coarse pearlite, what other types of structures may form in the coarse pearlite region?

Answer 4

Coarse ferrite cementite or any coarse structures

Question 5

On any I-T diagram, what steel structure is present before its temperature-time line cross either C curve?

Answer 5

100% Austenite

Question 6

What are the four regions in the region of transformation?

Answer 6

Coarse pearlite region, the fine pearlite region, the bainite region and the martensitic region.

Question 7

Describe what occurs when a sample of steel is quenched and it reaches the 50% transformation line on an I-T diagram.

Answer 7

The steel is transformed into half austenite and other half will be martensite.

Question 8

Which transformation product has more ductility, bainite or martensite? Which has greater hardness?

Answer 8

Bainite is superior to martensite in ductility and toughness, but it is not as hard or strong.