What is work hardening?

• A. The softening of metal due to heating
• B. The strengthening and stiffening of metal due to repeated shaping
• C. The loss of ductility due to corrosion
• D. The application of heat to relieve stress

Answer: (B)

Work hardening, also called strain hardening, is when metal becomes stronger and stiffer because it has been deformed plastically at room temperature. As you shape the metal—hammering, bending, or pulling—it accumulates dislocations in the crystal structure. These dislocations tangle and impede further movement of other dislocations, so the material’s yield strength and hardness increase. However, this also makes the metal less ductile and more resistant to further forming. It’s different from heating to soften (which lowers strength), corrosion-related brittleness, or stress-relief heating. In dent repair, repeated hammering can cause work hardening in a repaired area, which may require heating or other steps to restore formability.