(1) Work hardening
The influence of work hardening 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 crack of the steel pipe.
(2) Hydrogen embrittlement
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. Cold drawn steel pipes are one type of steel pipes, that is, one classified according to different production processes, which is different from hot rolled (expanded) pipes. It is formed by multi-pass cold drawing in the process of expanding the diameter of the capillary tube or the raw material tube, and is usually carried out on a single-chain or double-chain cold drawing machine of 0.5 to 100T. Cold-rolled (dial) steel pipe in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, mechanical processing pipe, thick-walled pipe, small diameter plus internal die cold drawn pipe other steel pipe It also includes carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless thin-walled steel pipes, and special-shaped steel pipes. Cold drawn steel pipe can have an outer diameter of 6mm and a wall thickness of 0.25mm. The outer diameter of the thin-walled pipe can be up to 5mm and the wall thickness is less than 0.25mm. The precision and surface quality are obviously better than the hot-rolled (expanded) pipe, but the process is affected. Restricted, its caliber and length are subject to certain restrictions.