What effect does cold working of steel plates have on the metal?

Cold working refers to the process of deforming metals at temperatures below their recrystallization temperature, which leads to changes in the properties of the material. One of the primary effects of cold working on steel plates is the increase in hardness. This phenomenon occurs due to the introduction of dislocations—defects in the crystal structure of the metal—during the deformation process. As the material is worked, these dislocations interact, making it more difficult for the layers of atoms to slide past one another, which is a key factor in increasing hardness.

Additionally, cold working leads to strain hardening (also known as work hardening), where the strength and hardness of the steel increase while the ability to deform plastically (ductility) typically decreases. This is particularly important in engineering applications, as hardening can improve wear resistance for components subjected to heavy loads or friction.

While cold working can indeed improve toughness in certain conditions, the most significant and consistent effect is the increase in hardness. Therefore, the choice indicating that the cold working makes the steel plates harder accurately reflects the primary outcome of the process.