What is the process called when copper conductors are heated to over 700°F (371°C) and then cooled to improve flexibility?

What is the process called when copper conductors are heated to over 700°F (371°C) and then cooled to improve flexibility?

• A. Quenching
• B. Work hardening
• C. Preheating
• D. Annealing

Answer: (D)

Annealing is the heat-treating process that softens copper by heating it to a sufficiently high temperature and then cooling it slowly. When copper conductors are heated to a temperature above about 371°C (700°F) and allowed to cool gradually, internal stresses from prior work are relieved and the crystal structure can recrystallize, increasing ductility so the wire becomes more flexible. Quenching—rapid cooling—tends to harden metals and reduce flexibility, so it wouldn’t achieve the desired softness. Work hardening is the strengthening that comes from deforming the metal; heating is used to reverse that effect, not to cause it. Preheating is a preparatory step used to reduce thermal shock in forming or welding, not the main method to improve flexibility.

Annealing is the heat-treating process that softens copper by heating it to a sufficiently high temperature and then cooling it slowly. When copper conductors are heated to a temperature above about 371°C (700°F) and allowed to cool gradually, internal stresses from prior work are relieved and the crystal structure can recrystallize, increasing ductility so the wire becomes more flexible. Quenching—rapid cooling—tends to harden metals and reduce flexibility, so it wouldn’t achieve the desired softness. Work hardening is the strengthening that comes from deforming the metal; heating is used to reverse that effect, not to cause it. Preheating is a preparatory step used to reduce thermal shock in forming or welding, not the main method to improve flexibility.