Question

Primary object of full annealing is to

• A. Improve surface finish and hardness
• B. Reduce ductility and resilience
• C. Increase toughness and yield point
• D. Increase ductility and machinability

Hint:

Full annealing softens metals by heating above the critical temperature and slow cooling, enhancing ductility and machinability while relieving internal stresses.

Answer 1

The Correct Option is D

Step 1: Understand the purpose of full annealing.
Full annealing is a heat treatment process applied to metals, typically steels, to reduce internal stresses, soften the material, and improve its properties. The process involves heating the material above its critical temperature, holding it at that temperature, and then slowly cooling it (usually in a furnace) to room temperature. Step 2: Analyze the effects of full annealing.
Softening: Full annealing reduces hardness by allowing the formation of a softer microstructure (e.g., ferrite and pearlite in steels).
Increase in ductility: The slow cooling relieves internal stresses and allows for recrystallization and grain growth, making the material more ductile.
Improve machinability: A softer, more ductile material is easier to machine, as it reduces tool wear and improves chip formation.
Other effects: Full annealing does not aim to increase hardness, surface finish, or yield point directly. It also does not reduce ductility or resilience; instead, it enhances them.
Step 3: Evaluate the options.
(1) Improve surface finish and hardness: Full annealing softens the material, reducing hardness, and does not directly improve surface finish (that’s more related to processes like polishing). Incorrect.
(2) Reduce ductility and resilience: Full annealing increases ductility and resilience by relieving stresses and softening the material. Incorrect.
(3) Increase toughness and yield point: While toughness may increase due to improved ductility, the yield point typically decreases because the material becomes softer. Incorrect.
(4) Increase ductility and machinability: This aligns with the primary goals of full annealing, as it softens the material, making it more ductile and easier to machine. Correct.
Step 4: Select the correct answer.
The primary object of full annealing is to increase ductility and machinability, matching option (4).