Question

Which one of the following statements is true? Explain whether each is true or false.

a] Pearlite and bainite are examples of phases that can be formed by austenite if the cooling rate
is controlled appropriately.
(b)
When austenite containing 1.2 percent carbon by weight (and no significant amounts of anyother alloying elements) is cooled slowly, hypereutectic Fe3C will form above 727�C.
(c)1040 plain carbon steel cannot be spheroidized.
(d)When a metal exhibits a single, well defined freezing temperature, all the crystals formed on cooling will have the same composition.
(e)The hardenability of 1060 plain carbon steeldoes not depend on the hardness of the sample at room temperature prior to heat treatment.

Answer 1

A. False: Pearlite and bainite cannot be regarded as phases. Instead they provide a description for microstructures of cementite and coexisting ferrite.

B. False: The element that will form in such condition is proeutectoid Fe3C

C. False: 1040 plain carbon steel can be spheroidized. To achieve this, it has to be austenitized and then cooled to a temperature below the eutectoid, and then held for a long period. When this is done, the precipitated carbide becomes spheroidal.

D. False: If you take a binary eutectic alloy and then you cool it down slowly, one would notice that all the material will become frozen below the eutectic temperature. However, there can be varying compositions formed from the two solid phases.

E. True: Before treating with heat, the hardness of the sample will be dependent on the initial microstructure. However, during the phase of austenitization, the microstructure will be eliminated; a step needed as an overture to the formation of martensite.

Step-by-step explanation: