Seamless steel pipe for structural use in general structure and mechanical structure, a large number of structural steel pipe structures used in construction, machinery, transportation, aviation, oil exploitation and other industries. Seamless steel pipe type outer diameter 10.0mm-168.3mm thickness in cold drawing. In the production process of precision steel pipes, there are cold work hardening and hydrogen embrittlement, which are the main causes of cracking of cold drawn seamless steel pipe. This article analyzes two phenomena and proposes some measures to prevent cracking of cold-drawn small-diameter seamless steel tubes. Analysis of the bursting phenomenon The cold drawn seamless steel pipe is formed by shrinking the diameter of the precision steel pipe with a small diameter through a drawing die, and the process route is generally annealing, pickling, and drawing. In the process of drawing, the cold-drawn small-diameter seamless steel pipe sometimes has the same rapid cracking phenomenon from the beginning to the end, and we call this phenomenon unified as cracking.
The reasons for cracking are: (1) work hardening; (2) hydrogen embrittlement.
a. The effect of work hardening
The seamless steel tube produces a large amount of plastic deformation during cold drawing, causing obvious lattice distortion, which increases the lattice energy and increases the internal energy of the metal, resulting in uneven internal stress of the metal and residual internal stress. This increases the hardness of the metal and reduces the toughness. The higher the hardness of the metal, the greater the residual internal stress during cold drawing and the more obvious the work hardening phenomenon. When the residual stress reaches a certain value, the metal will tear along a certain grain boundary to form a seamless steel pipe.
b. Effect of Hydrogen Embrittlement
During the process of descaling with acid, sulfuric acid and iron react to evolve hydrogen. Hydrogen penetrates into the steel in the form of atoms or ions to form a solid solution. The effect of hydrogen on the mechanical properties of steel is typically manifested in hydrogen embrittlement.
