The metal deforms plastically during cold drawing, and multiple slip systems start inside the crystal. The dislocation motion intercepts each other, causing dislocation jamming, and the dislocation source stops acting at the same time. The above-mentioned series of processes led to a decrease in the dislocation mobility and a significant increase in the density of dislocations in the crystal. When the plastic deformation further occurs, the stress increases enough to start the movement of the pinned dislocations, the screw dislocations intersect and slip, and the blade dislocations cannot intersect and slip, so that the dislocations intersect and the fixed order increases. Therefore, through the cold drawing process, the internal dislocation density of the metal is increased, and the dislocation mobility is reduced. It is difficult to generate dislocations and it is difficult to move the dislocations, so the hardness and strength of the metal material are improved.