MCQ Questions and Answers on Engineering Metallurgy

Answer :   Option:- C

Different phases of steel have distinct crystal structures that affect their mechanical properties. Martensite, formed through rapid cooling, has a body-centered tetragonal (bct) structure. Cementite, an iron carbide, has an orthorhombic structure. Austenite, which exists at high temperatures, has a face-centered cubic (fcc) structure, while Ferrite, a form of pure iron, has a body-centered cubic (bcc) structure. Understanding these structures helps in determining how steel behaves under various conditions, such as strength, toughness, and hardness.

Answer :   Option:- B

Nucleation refers to the process where new phases or structures form in a material, typically in materials like metals or liquids. There are two main types- Homogeneous nucleation and Heterogeneous nucleation. In homogeneous nucleation, new phase formation occurs uniformly throughout the material. In contrast, heterogeneous nucleation happens on surfaces or impurities within the material. Understanding these processes is important in fields like material science and engineering, as they significantly influence properties like strength and thermal conductivity.

Answer :   Option:- D

Etching is a common metallographic technique that uses chemical solutions to reveal the microstructure of metals. When a metal sample is immersed in an etchant, the surface reacts differently depending on the grain structure and phase composition of the material. This process helps to highlight features like grain boundaries, phases, and defects, allowing for detailed analysis under a microscope. Etching is crucial in materials science for examining how a material's internal structure influences its properties and performance.

Answer :   Option:- B

The boundary line between the liquid+solid and solid regions in a phase diagram is part of the solidus line. The solidus indicates the temperature below which the material is completely solid, and above which it exists as a mixture of solid and liquid.

Answer :   Option:- A

The transformation of austenite to bainite begins with the nucleation of ferrite at the grain boundaries of austenite. Bainite forms when the cooling rate is moderate, faster than pearlite but slower than martensite formation.

Answer :   Option:- B

The melting point of pure iron is approximately 1535°C. This is the temperature at which iron transitions from a solid to a liquid phase under normal atmospheric pressure.

Answer :   Option:- C

Nitriding is a surface hardening process that does not require quenching to obtain the final case hardness. It involves introducing nitrogen into the surface of the steel, forming a hard nitride layer without the need for rapid cooling.

Answer :   Option:- D

Gray cast iron is characterized by graphite in the form of flakes. This gives it a gray appearance and improves machinability, though it also reduces its strength and ductility compared to other cast irons with different forms of graphite.

Answer :   Option:- A

The boundary line between the alpha and alpha+beta regions must be part of the solvus curve. The solvus line indicates the limits of solid solubility between phases, such as alpha and beta, in an alloy system.

Answer :   Option:- D

The Gibbs phase rule for a general system is given by P + F = C + 2, where P is the number of phases, F is the number of degrees of freedom, and C is the number of components in the system. This equation helps determine the number of independent variables in a system at equilibrium.