Reasons for cracking of high precision cold drawn tube

- May 16, 2020-

High-precision cold-drawn tube is a drawing die, made of seamless steel pipe with a small diameter, usually processed by annealing, pickling and drawing. In the process of drawing cold-drawn small-diameter seamless steel tubes, cracks sometimes appear from the head to the tail like a bamboo pole. What is the reason for this phenomenon?

1. Work hardening

High-precision cold-drawn tube undergoes plastic deformation during cold-drawing, causing lattice distortion, increasing lattice energy and increasing energy in the metal, resulting in uneven residual stress in 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, resulting in cracking during work hardening.

2. Hydrogen embrittlement

The role of hydrogen embrittlement is that hydrogen and iron react with hydrogen in the process of removing scale from the 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 manifested as hydrogen embrittlement. High-precision cold-drawn tubes are different from hot-rolled (expanded) tubes. During the expansion of billets or raw material tubes, multiple cold-drawing processes are required. The outer diameter can be 6mm, the wall thickness can be 0.25mm, the outer diameter of the thin-walled tube can reach the size of 5mm wall thickness less than 0.25mm, the accuracy and surface quality are high, the length and length of the tube are limited by the process.