This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Brittle Fracture and Impact Testing – Temper Embrittlement”.
1. The fracture in tempered embrittlement steel is generally transgranular and propagates along the prior austenite grain boundary.
Explanation: The crack does propagate along the austenitic grain boundary, but the nature of crack is intergranular. The tempered embrittlement occurs because of the presence of specific impurity.
2. Which of the following is not an embrittlement element in steel?
Explanation: The antimony, phosphorus, tin, and arsenic are chief embrittling materials present in the steel. Plane carbon steel with less than 0.5% manganese is not susceptible to tempered embrittlement.
3. Which of the following element does not increase the susceptibility of steel towards temper embrittlement?
Explanation: The chromium and manganese are most helpful in decreasing the embrittlement tendency of steel. To a lower extent, nickel also helps, but carbon has no direct effect on increasing the resistance to embrittlement.
4. The body-centered cubic and hexagonal closed packed structure are more prone to hydrogen embrittlement than FCC.
Explanation: The above statement is true; the BCC and FCC are more prone to hydrogen embrittlement than FCC. As low as 0.001 percentage of hydrogen is sufficient to cause the embrittlement in the material.
5. The hydrogen embrittlement is most severe ___________
a) near zero kelvin temperature
b) at room temperature
c) well above room temperature
d) near the melting point of material
Explanation: The hydrogen embrittlement is ineffective at too low and too high temperatures. At room temperature, the hydrogen embrittlement is most severe.
6. In the hydrogen embrittlement of the metals, the hydrogen is present in form of ________
Explanation: In hydrogen embrittlement, the monoatomic hydrogen is absorbed on the surface by chemical absorption method. This is because the diffusion of nascent hydrogen atom is much easier than bulky hydrogen gas molecules.
7. The fracture form from hydrogen embrittlement cannot be ___________ type.
Explanation: Depending on stress level and loading, the hydrogen embrittlement fracture can be ductile, brittle intergranular. But the creep is phenomena associated with high temperature and at high-temperature hydrogen embrittlement is negligible.
8. Which of the following fracture is assisted by chemical attack?
c) Stress-corrosion cracking
d) Neutron embrittlement
Explanation: The stress corrosion cracking is a combined effect of chemical attack and applied stress. The chemical breaks the protective oxide layer of surface and form gradient of ion concentration in crack tip with surface. This causes the localized corrosion which accelerates the rate of cracking.
9. The liquid metal embrittlement is a combined effect of solid metal surface attacked by _________
a) organic liquid
b) inorganic liquid
c) liquid metal
d) low melting point metal
Explanation: The molten metal embrittlement results when the solid surface of the metal is wetted by the lower melting point metal. For example, brass 70-30 fails in an intergranular brittle fracture when wetted by mercury.
10. Which of the following is embrittlement material for liquid metal embrittlement?
Explanation: The embrittlement metals are of low melting point, having high diffusivity in metal to be embrittlement. So Gallium has a melting point around room temperature, while sodium and tin also have very low melting point. But the copper has a high melting point, so it does not satisfy the condition.
11. The degree of neutron embrittlement ____________ with increases in temperature.
c) remains the same
d) no relationship
Explanation: The degree of neutron embrittlement decreases with increasing temperature of exposure. Also, it increases with increases in the neutron flux x time.
12. Which of the following material is best to manufacture the core-shell chamber for the nuclear reactor?
a) Ferritic stainless steel
b) Austenitic stainless steel
c) Tempered martensitic steel
d) High chromium steel
Explanation: The tempered martensitic stainless steel with low initial transition temperature and finer grain size provides the best resistance to neutron embrittlement.
Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.
To practice all areas of Mechanical Metallurgy, here is complete set of 1000+ Multiple Choice Questions and Answers.
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