This set of Manufacturing Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Heat Treatment”.
1. Which of the following is the hardest constituent of steel?
Explanation: Martensite is the hardest constituent of steel. The primary reasons accounting for this could be, the internal strains within BCC iron due to the excess carbon presence and due to the plastic deformation of parent FCC iron (austenite) surrounding the martensitic plate. Rate of cooling and the amount of carbon percentage in steel are directly proportional to the amount of hardness achieved in martensitic transformation.
2. Iron possesses BCC crystal structure up to (in degree centigrade)?
Explanation: Pure iron possess either BCC or FCC crystal structure as its temperature is increased from room temperature to its melting point. At room temperature to 910oC, it is having BCC, between 910oC and 1410oC it is having face centered cubic, and from 1410oC to its melting point (1539oC) it returns to its BCC crystal structure.
3. Iron possesses BCC crystal structure above (in degree centigrade)?
Explanation: From 1410oC to its melting point (1539oC) iron is having BCC crystal structure.
4. Iron possesses FCC crystal structure above (in degree centigrade)?
Explanation: Between 910oC and 1410oC iron is having face centered cubic crystal structure.
5. Which of the following form of iron is magnetic in nature?
Explanation: The alpha form of iron is magnetic and stable at all temperatures below 910oC.
6. For steel, which one of the following properties can be enhanced upon annealing?
Explanation: A furnace cooling technique, annealing will enhance the ductility of steel, due to the formation of coarse pearlite.
7. In Annealing, cooling is done in which of the following medium?
Explanation: In annealing, after solutionising, material is used to furnace cool, means furnace is switched off and the steel sample inside is let cool down.
8. In normalizing, cooling is done in which of the following medium?
Explanation: In normalizing, steel is heat treated above its critical temperature, solutionised, and then allowed to cool for a long time by keeping it in air. In steel, it forms fine pearlite, which imparts strength to steel.
9. Mild steel can be converted into high carbons steel by which of the following heat treatment process?
c) Case hardening
Explanation: Case hardening, also referred as carburizing increases carbon content of steel, thus, imparting hardness to steel.
10. Upon annealing, eutectoid steel converts to which of the following?
Explanation: Eutectoid steels upon annealing produces pearlite (coarse pearlite). Pearlite is an alternate lamellae of ferrite and cementite.
Sanfoundry Global Education & Learning Series – Manufacturing Engineering.
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