Q1: Which of the following terminology is used for the temperature at which new grains are formed in a metal ?

ANS:C - Recrystallisation temperature.

Recrystallization temperature is the temperature at which recrystallization occurs in a metal. Recrystallization is a phenomenon in metallurgy where the deformed grains within a metal undergo a process of grain growth and restructuring, resulting in the formation of new, strain-free grains. This process is important for improving the mechanical properties of metals, such as increasing ductility, reducing hardness, and improving formability. Here's an explanation of recrystallization temperature and its significance:

1. Formation of Deformed Grains: When a metal undergoes plastic deformation through processes such as rolling, forging, or extrusion, the metal grains experience distortion and elongation. This deformation introduces internal stresses and defects within the grains, such as dislocations and grain boundaries.
2. Initiation of Recrystallization: As the temperature of the deformed metal is increased, the energy within the metal also increases. At a certain critical temperature known as the recrystallization temperature, the energy becomes sufficient to overcome the barriers to grain boundary movement and nucleation of new grains. This initiates the process of recrystallization.
3. Grain Growth and Restructuring: During recrystallization, the deformed grains begin to transform into new, strain-free grains with lower dislocation densities. The movement of grain boundaries facilitates the migration and rearrangement of atoms, leading to the growth of new grains. As recrystallization progresses, the original deformed grains are replaced by a new set of equiaxed grains with uniform orientation.
4. Significance in Material Properties: Recrystallization plays a crucial role in improving the mechanical properties of metals. By eliminating the defects and internal stresses introduced during plastic deformation, recrystallization increases the ductility, formability, and toughness of the metal. It also leads to a reduction in hardness and an improvement in the material's ability to undergo further processing, such as machining or forming.
5. Control and Optimization: The recrystallization temperature is influenced by various factors, including the type of metal, its composition, and the degree of prior deformation. Metallurgists often study and optimize the recrystallization process to achieve desired material properties for specific applications. Controlling parameters such as deformation temperature, strain rate, and annealing time can help manipulate the recrystallization behavior and tailor the material properties accordingly.

In summary, recrystallization temperature is the temperature at which recrystallization occurs in a metal, leading to the formation of new, strain-free grains and the improvement of mechanical properties. Understanding and controlling the recrystallization process is essential for optimizing the properties and performance of metallic materials in various industrial applications.