The high-precision cold drawn tube is made of a small diameter seamless steel tube using a drawing die, usually processed by annealing, pickling and drawing. During the drawing process of cold-drawn small-diameter seamless steel pipes, cracking from the head to the tail like bamboo poles sometimes occurs. What is the reason for this phenomenon?
1. Work hardening
The high-precision cold drawn tube is plastically deformed during cold drawing, causing lattice distortion, increasing lattice energy, and increasing energy in the metal, resulting in uneven residual stress in the metal. This increases the hardness of the metal and reduces the toughness. The higher the hardness of the metal, the greater the residual stress, which leads to cracking in the work hardening.
2, hydrogen embrittlement
The effect of hydrogen embrittlement is that hydrogen and iron react with hydrogen during the process of removing scale from an acidic solution. 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 usually characterized by hydrogen embrittlement. The high-precision cold drawn tube is different from the hot-rolled (expanded) tube, and a multi-pass cold drawing process is required in the process of expanding the blank or raw material pipe. The outer diameter can be 6mm, the wall thickness can be 0.25mm, the outer diameter of the thin-walled tube can reach 5mm wall thickness less than 0.25mm, the precision and surface quality are high, and the length and length of the tube are limited by the process.