This set of Heat Treatment of Metals and Alloys Multiple Choice Questions & Answers (MCQs) focuses on “Steels – Factors Affecting TTT Diagram”.
1. Which one of the following statements is correct?
a) As the amount of carbon increases in the steel, the lower part of TTT diagram shifts upwards
b) As the amount of carbon increases in the steel, the lower part of TTT diagram shifts downwards
c) As the amount of Aluminium increases in the steel, Ms temperature in TTT diagram shifts downwards
d) As the amount of carbon increases in the steel, the Ms temperature of TTT diagram remains constant
View Answer
Explanation: As the amount of carbon increases in the steel, the lower part of TTT diagram shifts downwards. Also, the Ms temperature is decreased. Almost all alloying elements show same behavior except Aluminium.
2. Which one of the following statements is incorrect for TTT diagrams?
a) Addition of Nickel lower the upper part of the TTT curve
b) Addition of Manganese lower the upper part of the TTT curve
c) Addition of carbon lower the upper part of the TTT curve
d) Addition of carbon shifts the upper part of TTT curve upwards
View Answer
Explanation: Nickel, Manganese and carbon are austenite stabilizers. So as their concentration increases, the pearlitic C curve shifts downwards. This is the reason behind overlapping of pearlitic and bainitic C curve in plain carbon steels having these elements.
3. Which one of the following statements is correct?
a) As the grain size decreases, TTT curve shifts towards right
b) As the grain size decreases, TTT curve shifts towards left
c) As the grain size Increases, TTT curve shifts towards left
d) Grain size does not have any effect on TTT curve
View Answer
Explanation: As the grain size decreases, TTT curve shifts towards left. The reason behind this is the larger grain boundary area of fine grained steel which favors nucleation of pearlite, bainite, ferrite and cementite.
4. Which one of the following statements is correct?
a) As the heterogeneity of austenite increases, transformation time range increases
b) As the heterogeneity of austenite increases, transformation time range decreases
c) As the homogeneity of austenite increases, transformation time range increases
d) Homogeneity or heterogeneity does not have any effect on TTT curve
View Answer
Explanation: As the heterogeneity of austenite increases, transformation time range increases. It increases the transformation time range in diffusional transformation as well as the temperature range of shear transformation products.
5. The heterogeneity of austenite when heated to temperatures around austenising temperatures improves the ductility and the machinability of high carbon steels.
a) True
b) False
View Answer
Explanation: The heterogeneity of austenite when heated to temperatures around austenising temperatures is an advantage as it allows obtaining sphereodized pearlite by decomposition within 50oc below austenising temperature. Therefore, ductility and the machinability of high carbon steels are improved.
6. Which one of the following statements is incorrect?
a) Fine grained steels promote the formation of ferrite from austenite
b) Fine grained steels promote the formation of pearlite from austenite
c) Coarse grained steels promote the formation of ferrite from austenite
d) Fine grained steels shifts the TTT curve to left
View Answer
Explanation: Fine grained steels promote the formation of ferrite and cementite. This is the reason why decrease in grain size shifts the TTT curve to left.
7. Which one of the following statements is incorrect?
a) As the grain size increases, critical cooling rate increases
b) As the grain size increases, critical cooling rate decreases
c) As the grain size increases, critical cooling rate remains the same
d) As the grain size increases, critical cooling rate may increase or decrease
View Answer
Explanation: Critical cooing rate is obtained by drawing a tangent at the nose of the curve. So as the grain size decreases, the nose shifts to the left. Therefore CCR increases since the slope of the tangent increases.
8. Which one of the following phenomenon does not happen when the TTT curve shifts to right?
a) Increases in hardenability
b) Increase in ease of forming martensite
c) Increase in severity of cooling rate to form martensite
d) Decrease in severity of cooling rate to form martensite
View Answer
Explanation: As the TTT curve shifts to right, the CCR decreases as the slope of the tangent at the nose decreases. Therefore there is a decrease in the severity of cooling rate to form martensite. Therefore there is an increase in ease to form martensite and thus the hardenability increases.
Sanfoundry Global Education & Learning Series – Heat Treatment of Metals and Alloys.
To practice all areas of Heat Treatment of Metals and Alloys, here is complete set of Multiple Choice Questions and Answers.
