The Causes of Cold Cracking of Small Diameter Seamless Steel Tubes in the Drawing Process

In the production process of cold-drawn seamless tubes, there are cold work hardening and hydrogen embrittlement phenomena, which are the main reasons for the cracking of the seamless tube. This article analyzed two phenomena and put forward some measures to prevent cracking of small-diameter seamless steel tubes.

Burst phenomenon analysis cold-drawn seamless pipe is formed by reducing the diameter of the seamless steel pipe through a drawing die, and the process route is generally annealing, pickling, and drawing. In the process of drawing cold-drawn small-diameter seamless steel tubes, cracks may begin to crack as much as the bamboo ridges from head to tail. We call this phenomenon collectively cracking.

The reasons for the cracking are:
(1) Work hardening;
The influence of work hardening on the steel pipe during cold drawing produces a large number of plastic deformations, causing significant lattice distortions, thereby increasing the lattice energy and increasing the internal energy of the metal, resulting in nonuniform metal internal stress and residual internal stress. This increases the hardness of the metal and decreases its toughness. The higher the metal hardness, the greater the residual internal stress during cold drawing, the more obvious the work hardening phenomenon. When the residual stress reaches a certain value, the metal will tear along a certain column of grain boundaries, forming a crack in the steel pipe.

(2) Hydrogen embrittlement.
Effect of hydrogen embrittlement phosphoric acid reacts with iron to evolve hydrogen during descaling with acid. Hydrogen penetrates into the steel as atoms or ions to form a solid solution. The effect of hydrogen on the mechanical properties of steel is typically manifested in hydrogen embrittlement.