A) tempering
B) annealing
C) quenching
D) case hardening
Correct Answer: D
Solution :
Case hardening In case hardening technique, iron rods embedded in charcoal powder are heated repeatedly. This technique is used in making axles of railway wagon. Annealing A process in which the newly shaped articles are cooled slowly. If they are cooled quickly they become brittle on account of the high internal strain. Tempering The method of reheating a quenched steel to relieve internal stresses, reduce hardness, and tensile strength and restore ductility and resistance to impact loading. It is carried out within the temperature range \[200-{{550}^{o}}C\] for plain carbon steels. Quenching In this method a steel article is heated to redness and then suddenly cooled by plunging into water, the steel becomes hard and brittle.
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