Which heat-treating operation alters the surface of metal chemically by introducing a high carbide or nitride content?

Which heat-treating operation alters the surface of metal chemically by introducing a high carbide or nitride content?

• A. Normalizing
• B. Case hardening
• C. Annealing
• D. Quenching

Answer: (B)

The heat-treating operation that chemically alters the surface of metal by introducing a high carbide or nitride content is case hardening. This process involves diffusing carbon or nitrogen into the surface of the steel at high temperatures, which significantly enhances surface hardness while maintaining a tough interior. Case hardening is commonly used for gears and other components that must withstand high surface stresses because it provides a hard, wear-resistant layer that can endure mechanical wear and fatigue. The carbon or nitrogen diffuses into the outer layer, creating a hardened case, while the core remains softer and more ductile, allowing for better impact resistance. Normalizing, annealing, and quenching are processes that primarily focus on altering the microstructure of the metal to modify its properties, such as hardness or brittleness, but do not involve the chemical alteration of the surface composition to the same extent as case hardening does.

The heat-treating operation that chemically alters the surface of metal by introducing a high carbide or nitride content is case hardening. This process involves diffusing carbon or nitrogen into the surface of the steel at high temperatures, which significantly enhances surface hardness while maintaining a tough interior.

Case hardening is commonly used for gears and other components that must withstand high surface stresses because it provides a hard, wear-resistant layer that can endure mechanical wear and fatigue. The carbon or nitrogen diffuses into the outer layer, creating a hardened case, while the core remains softer and more ductile, allowing for better impact resistance.

Normalizing, annealing, and quenching are processes that primarily focus on altering the microstructure of the metal to modify its properties, such as hardness or brittleness, but do not involve the chemical alteration of the surface composition to the same extent as case hardening does.