How Much Do You Know About the Causes of Cracking in Precision Steel Tubes?

Those who frequently work with precision steel tubes likely have their own understanding of the drawbacks of these tubes. One common issue with precision steel tubes is their tendency to crack. Once a precision steel tube cracks, it needs to be repaired, and the process can be quite cumbersome. What factors contribute to the cracking of these tubes? Let’s take a look at the following explanations.

Influence of Work Hardening

During the cold drawing process, the steel tube undergoes significant plastic deformation, causing noticeable lattice distortion. This increases the lattice energy and the internal energy of the metal, leading to uneven internal stress and the generation of residual internal stress. Consequently, the hardness of the metal increases while its toughness decreases. The higher the hardness of the metal, the greater the residual internal stress during cold drawing, and the more pronounced the work hardening phenomenon becomes. When the residual stress reaches a certain level, the metal will tear along a series of grain boundaries, resulting in the cracking of the steel tube.

Influence of Hydrogen Embrittlement

During the acid pickling process to remove oxide scale, sulfuric acid reacts with iron, releasing hydrogen gas. Hydrogen penetrates the steel in atomic or ionic form, forming a solid solution. The typical effect of hydrogen on the mechanical properties of steel is manifested in hydrogen embrittlement. Cold-drawn steel tubes are a type of steel tube classified based on their manufacturing process, distinct from hot-rolled (expanded) tubes. They are produced through multiple stages of cold drawing of the raw tube billet or raw material tube, typically on single-chain or double-chain cold drawing machines with capacities ranging from 0.5 to 100 tons. Cold-drawn (rolled) steel tubes include general steel tubes, low and medium-pressure boiler tubes, high-pressure boiler tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, machined tubes, thick-walled tubes, small-diameter cold-drawn tubes with inner molds, and other types of tubes. In addition, they encompass carbon thin-walled tubes, alloy thin-walled tubes, stainless thin-walled tubes, and profiled tubes. The outer diameter of cold-drawn steel tubes can reach 6 mm, with wall thicknesses up to 0.25 mm. Thin-walled tubes can have an outer diameter of 5 mm and wall thicknesses less than 0.25 mm. The dimensional accuracy and surface quality of cold-drawn tubes are significantly better than those of hot-rolled (expanded) tubes, although the diameter and length are limited by the manufacturing process.