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Analysis of the causes of cracking of high-precision cold drawn tubes
High-precision cold drawn pipes are made from seamless steel pipes with smaller diameters using drawing dies and are usually processed by annealing, pickling and drawing. During the drawing process of cold-drawn small-diameter seamless steel pipes, cracks sometimes appear from the head to the tail like bamboo poles. What is the reason for this phenomenon?
1. Work hardening
High-precision cold-drawn tubes produce plastic deformation during the cold-drawing process, causing lattice distortion, which increases the lattice energy and the energy within the metal, resulting in uneven residual stress within the metal. In this way, the hardness of the metal is increased and the toughness is reduced. The higher the hardness of the metal, the greater the residual stress, leading to cracking during work hardening.
2. Hydrogen embrittlement phenomenon
Hydrogen embrittlement occurs when hydrogen and iron react with hydrogen during the removal of scale from an acidic solution. Hydrogen penetrates into the steel in the form of atoms or ions, forming a solid solution. The effect of hydrogen on the mechanical properties of steel is usually manifested as hydrogen embrittlement. High-precision cold-drawn pipes are different from hot-rolled (expansion) pipes. During the diameter expansion process of the blank or raw material pipe, a multi-pass cold drawing process is required. The outer diameter can be 6mm and the wall thickness can be 0.25mm. The outer diameter of the thin-walled tube can reach 5mm with a wall thickness less than 0.25mm. The precision and surface quality are high. The length and length of the tube are limited by the process.
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