Which process increases metal hardness by plastic deformation without removing material?

• A. Weight
• B. Weaving
• C. Work hardening
• D. Wood recycling

Answer: (C)

Work hardening, also known as strain hardening, is the process where a metal becomes harder and stronger due to plastic deformation performed below its recrystallization temperature, without removing material. The deformation creates a tangled network of dislocations that impedes further motion, raising hardness and yield strength while the total mass stays the same. This is typical of cold working methods like rolling, bending, or hammering. Other options don’t fit because they aren’t metalworking processes that increase hardness through plastic deformation (weighting isn’t a metal process, weaving is textile-related, and wood recycling concerns wood materials).