Red Seal Tool and Die Maker Practice Exam

What effect does cold working have on the ductility of a metal?

1. It increases ductility

2. It decreases ductility

3. It has no effect on ductility

4. It transforms ductility into brittleness

The correct answer is: It decreases ductility

Cold working refers to the process of deforming a metal at temperatures lower than its recrystallization temperature, typically at room temperature. During this process, dislocations in the metal's crystal structure accumulate, which hinders the movement of these dislocations. As a result, the metal becomes harder and stronger due to work hardening. However, this increase in strength comes at the cost of decreased ductility. Ductility is a measure of a material's ability to deform under tensile stress, and while the metal can become stronger through cold working, the dislocation density inhibits further deformation. Consequently, the ability of the metal to undergo additional plastic deformation without fracturing is reduced, resulting in decreased ductility. This relationship between increased strength and decreased ductility during cold working is critical for manufacturing processes, as it influences the design and selection of materials for various applications. Understanding the impact of cold working helps tool and die makers to anticipate how a material will behave during different machining processes.