Cold Drawn Tubes

Product Specification

Principles of Metallurgy

Cold-drawn steel pipes are work-hardened. During cold drawing, the metal undergoes plastic deformation, and multiple slip systems are activated inside the crystal, and the dislocation movements intercept each other, and many dislocations are pinned, resulting in dislocation accumulation, and at the same time, the dislocation source stops moving. The above-mentioned series of processes lead to a decrease in the mobility of dislocations and a significant increase in the dislocation density in the crystal. When the plastic deformation occurs further, the stress increases enough to make the pinned dislocations start to move, and the screw dislocations slip, but the edge dislocations cannot slip, so the dislocations intersect, and the immobility order increases.

Therefore, the dislocation density inside the metal is increased by cold drawing, and the mobility of dislocations is reduced. It is difficult to generate dislocations and move dislocations, so the hardness and strength of metal materials are improved. This is the metallurgical principle of cold drawing.

Mechanics

During cold drawing, the steel pipe passes through a mold of a certain shape and size under the action of force and undergoes plastic deformation. The drawing methods in production can be roughly divided into three types: reducing diameter drawing, reducing outer wall drawing, and reducing inner wall drawing. The deformation mostly goes through three stages of diameter reduction, wall reduction, and sizing, and corresponding stresses are generated inside the deformation zone, in which the axial direction is tensile stress, and the radial and circumferential directions are compressive stress. Two-dimensional compressive stress state, which is the basic mechanical characteristic of the deformation process of cold-drawn tubes.

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