Cold working of metals — effects on mechanical properties In manufacturing and materials engineering, cold working (plastic deformation below the recrystallisation temperature) tends to alter several properties. Which of the following increases due to cold working?

Introduction / Context:
Cold working, also called work hardening or strain hardening, is plastic deformation carried out at a temperature below the metal’s recrystallisation temperature. It is widely used to strengthen sheets, wires, and fasteners without adding alloying elements. Understanding which properties increase or decrease is vital for selecting subsequent heat treatments and predicting service behaviour.

Given Data / Assumptions:

• Deformation is below recrystallisation temperature (typically room temperature for steels and many non-ferrous alloys).
• No intermediate anneal is applied during the cold work.
• Microstructure accumulates dislocations and internal stresses.

Concept / Approach:
Work hardening raises the dislocation density. Dislocations interact and impede further motion, so a higher applied stress is required to continue plastic flow. Consequently, yield strength, tensile strength, and hardness increase. Ductility and impact toughness usually decrease, and electrical conductivity may decline in some alloys. Springback also increases due to a higher yield/elastic modulus ratio.

Step-by-Step Solution:
Identify property changes due to dislocation accumulation.Yield strength increases because more stress is needed to initiate plastic flow.Ultimate tensile strength increases as the entire stress–strain curve shifts upward.Hardness increases because resistance to indentation correlates with flow stress.Therefore, the correct comprehensive choice is “all of these”.

Verification / Alternative check:
Tensile tests on cold-rolled steels or drawn copper wires show higher proof stress and UTS after deformation; hardness numbers (e.g., Vickers or Rockwell) also rise proportionally to cold work percent.

Why Other Options Are Wrong:

• Tensile strength / Yield strength / Hardness individually: each is true but incomplete. The question asks what increases, and multiple properties increase together.
• Impact toughness: generally decreases due to reduced ductility and notch resistance.

Common Pitfalls:
Assuming all properties improve with cold work. In reality, ductility and toughness fall, and residual stresses may necessitate stress-relief or annealing steps.

Final Answer:
all of these