Phase Diagrams Theory

Question 1

Describe the AISI-SAE Steel Designation System (XYWZ)?

Answer 1

X: Group of carbon steel
Y: Amount of Alloy
WZ: Carbon Concentration to 0.01%

Question 2

Name the 3 main types of steel in terms of a phase diagram and give their carbon composition?

Answer 2

1. Eutectoid - 0.76%C
2. Hypoeutectoid - <0.76%
3. Hypereutectoid - >0.76%

Question 3

What is a steel and what phase do all compositions pass through?

Answer 3

Alloys of Iron with less than 2,14% carbon.

single phase austenite phase.

Question 4

Hypoeutectoid steel composition?

Answer 4

Ferrite+Pearlite

Question 5

Eutectoid Steel composition?

Answer 5

100% Pearlite where Pearlite is composed of Ferrite + Cementite

Question 6

Hypereutectoid steel?

Answer 6

Pearlite +Cementite

Question 7

Use of Isothermal Transformation Diagram

Answer 7

Predicts what structure is produced on non-equilibrium cooling from austenite.

Question 8

Name the treatment used on martensite. Describe the 3 main attributes of this treatment. What is the main outcome of of this treatment?

Answer 8

Tempering.

1. Holding at an intermediate temperature below 723 degreesC.
2. Reduces internal stresses caused by quenching (relaxing material).
3. Some Carbon comes out of material.

Sacrifices some strength and hardness for increased toughness yielding tempered martensite.

Question 9

What does the slow cooling, moderate cooling and rapid cooling (quenching) of Austenite yield? (Give their composition

Answer 9

Slow: Pearlite
Moderate: Bainite
Rapid quench: Martensite

Question 10

Give the general trend of increasing strength and decreasing ductility for 6 material phases?

Answer 10

Marteniste
Tempered Martensite
Bainite
Fine Pearlite
Course Pearlite
Spheroidite