This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Nitriding, Cyaniding and Carbonitriding – 2”.
1. Which of the following does not apply to cyaniding?
a) Requires less time
b) Operated at lower temperatures
c) Low corrosion resistance
d) Costly process
View Answer
Explanation: The cyaniding process is an expensive process of surface hardening of steels which is applied to produce automobile parts. It requires lesser time and lower temperatures than carburizing. It also lowers warping and distortion while increasing the corrosion and wear resistance.
2. Gas cyaniding is otherwise known as __________
a) Nitriding
b) Carbonitriding
c) Induction Hardening
d) Flame Hardening
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Explanation: Carbonitriding is a surface hardening process that involves the diffusion of nitrogen and carbon into the steel. Carbonitriding may also be called as gas-cyaniding or dry-cyaniding.
3. How long is the heating process for carbonitriding done for?
a) 1-2 hours
b) 2-10 hours
c) 12-20 hours
d) 24-30 hours
View Answer
Explanation: The carbonitriding process is carried out in a gas atmosphere furnace using a carburizing gas such as propane or methane mixed with ammonia. The workpiece is heated to 850oC in the mixture of gases for 2-10 hours followed by quenching and tempering.
4. At what temperature is the workpiece tempered in carbonitriding process?
a) 180oC
b) 360oC
c) 540oC
d) 720oC
View Answer
Explanation: The carbonitriding process is carried out in a gas atmosphere furnace using a carburizing gas.The workpiece is heated to 850oC in the mixture of gases for 2-10 hours. This is followed by quenching to increase hardness, then by tempering at 180oC for reducing the brittleness.
5. What is the case depth obtained in the cyaniding process?
a) 0.38 mm
b) 0.25 mm
c) 0.5 mm
d) 1.25 mm
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Explanation: Of all the diffusion surface hardening methods, carburizing provides the highest cast depth of 1.38 mm. This is followed by carbonitriding, nitriding, and cyaniding at 0.5 mm, 0.38 mm, and 0.25 mm correspondingly.
6. What is the hardness achieved in the carbonitriding process?
a) HRC 35
b) HRC 65
c) HRC 105
d) HRC 140
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Explanation: Carbonitriding process of surface hardening results in a case depth of 0.5 mm and a hardness after heat treatment of HRC 65. Interestingly, carburizing and cyaniding also result in equal hardness after heat treatment.
7. What are the applications of nitriding?
a) Gears, camshafts
b) Valve guides and seatings
c) Chain links, nuts, bolts, and screws
d) Gears, nuts, bolts
View Answer
Explanation: Nitriding process provides an extreme hardness of the surface and a case depth of 0.38 mm. It is typically used for valve guides and seatings, and for gears.
8. Nitriding steels are tempered at about ________
a) 100-200oC
b) 300-450oC
c) 600-700oC
d) 800-950oC
View Answer
Explanation: Nitralloy steels are commonly used in nitriding process. These steels are hardened by oil quenching from 900oC and tempered at 600-700oCbefore nitriding.
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