# Mechanical Metallurgy Questions and Answers – Brittle Fracture and Impact Testing – Significance of Transition Temperature Curve

This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Brittle Fracture and Impact Testing – Significance of Transition Temperature Curve”.

1. The addition of carbon in steel ___________ the ductile to brittle transition temperature?
a) decreases
b) increases
c) remains the same
d) no relationship

Explanation: The addition of carbon has the most pronounced effect in increasing the ductile to brittle transition temperature of the steel. Every 0.1% addition of carbon increase the transition temperature by 14 degrees Celsius.

2. The addition of manganese in steel ___________ the ductile to brittle transition temperature?
a) decreases
b) increases
c) remain the same
d) no relationship

Explanation: The addition of manganese decreases the ductile to brittle transition temperature by 5 degrees Celsius with every 0.1% addition of manganese in the steel. The combination of carbon and manganese in steel gives the best result of strength and toughness.

3. In the following diagram, energy vs. temperature shows steel of three different compositions. Based on the curve, find the correct order of amount of carbon present in the steel?

a) C1>C2>C3
b) C3>C2>C1
c) C2>C3>C1
d) C1>C3>C2

Explanation: As the carbon content increases in the material, the ductile to brittle transition temperature also increases, along with that the impact energy of the steel decreases. Hence, the correct order of carbon composition is C3>C2>C1.

4. The addition of Phosphorus in steel ___________ the ductile to brittle transition temperature?
a) decreases
b) increases
c) remains the same
d) no relationship

Explanation: The addition of phosphorus has a strong effect in raising the DBTT of steel. It is observed that the addition of 0.01% P increases the ductile to brittle transition temperature by 7 degrees Celsius.

5. what is the order of ductile to brittle transition temperature for killed steel, semi-killed steel, and rimmed steel?
a) Killed steel>Semi-killed>Rimmed steel
b) Killed steel<Semi-killed<Rimmed steel
c) Rimmed steel >Killed steel>Semi-killed
d) Rimmed steel<Killed steel<Semi-killed

Explanation: The DBTT is strongly depended upon the oxygen content of the steel. As the oxygen percentage in steel increases, the transition temperature also increases. The rimmed steel contains the highest amount of oxygen than semi-killed and killed steel.
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6. If a steel having ASTM grain size number 5 have transition temperature equal to 20 degrees. For the same steel having ASTM grain size 10, the DBTT will be equal to __________
a) 20
b) 50
c) -50
d) Cannot predict

Explanation: As the ASTM grain size number increases, effectively the grain diameter decreases. Also, it is known that if the grain size is smaller, the ductile to brittle transition temperature will be lower; the DBTT temperature will be less than 20 degrees Celsius.

7. The strengthening mechanism i.e., the strain aging increases the strength and decreases the transition temperature of the metal.
a) True
b) False

Explanation: The strain aging does increase the strength of the metal, but also increases the ductile to brittle transition temperature around 30 degrees in heavily cold worked strain hardened materials.

8. The blue brittleness is phenomena observed in _____________
a) low carbon steel
b) copper
c) zinc
d) aluminum

Explanation: The blue brittleness is the phenomena of loss of impact strength observed in low carbon steel when it is heated in range of 230 to 370 degrees. This is because of accelerated strain aging at this temperature.

9. A material with higher thickness will have a higher impact toughness compared to sample with lower thickness of the same material.
a) True
b) False

Explanation: Generally, it’s the reverse i.e., the material with higher thickness shows lower impact strength than the material with smaller thickness made up of the same material. This can be due to higher chances of triaxle state of stress in the thick section than the thin section.

10. The dynamic tear test is the test used to measure the _______________
a) tensile strength
b) fatigue strength
c) impact strength
d) creep strength

Explanation: The dynamic tear test is a larger version of the Charpy impact test. This test is used to measure the impact strength of much larger thickness samples, whereas in the Charpy test the sample thickness is limited to 1 cm only.

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