Comparison of Cold Drawing and Hot Rolling Processes for Seamless Steel Pipe

Seamless steel pipe material: Seamless steel pipe is made of steel ingot or solid tube billet by perforation into rough tube, and then hot rolled, cold rolled or cold drawn. The material is generally made of high-quality carbon steel such as 10, 20, 30, 35, 45, low alloy structural steel such as 16Mn, 5MnV or alloy steel such as 40Cr, 30CrMnSi, 45Mn2, 40MnB by hot rolling or cold rolling. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid delivery pipelines.
Usually, the production process of seamless steel pipes is divided into two types: cold drawing process and hot rolling process. The following is an overview of the process flow of cold-drawn seamless steel pipes and hot-rolled seamless steel pipes:
Cold-drawn (cold-rolled) seamless steel pipe process: tube billet preparation and inspection → tube billet heating → perforation → tube rolling → steel pipe reheating → sizing (reducing) diameter → heat treatment → finished tube straightening → finishing → inspection (non-destructive, physical and chemical, bench inspection) → storage
Cold-rolled seamless steel pipe billets must first be subjected to three-roll continuous rolling, and sizing tests must be performed after extrusion. If there is no response crack on the surface, the round tube must be cut by a cutting machine and cut into billets with a length of about one meter. Then enter the annealing process. Annealing must be pickled with acidic liquid. During pickling, pay attention to whether there is a large amount of bubbles on the surface. If there is a large amount of bubbles, it means that the quality of the steel pipe does not meet the corresponding standards.
Hot-rolled (extruded) seamless steel pipe process: round tube billet → heating → perforation → three-roll oblique rolling, continuous rolling or extrusion → tube removal → sizing (or reducing) diameter → cooling → billet tube → straightening → water pressure test (or flaw detection) → marking → storage
Hot rolling, as the name implies, has a high temperature for the rolled piece, so the deformation resistance is small and a large deformation amount can be achieved. The delivery state of hot-rolled seamless steel pipes is generally hot-rolled and heat-treated before delivery. The solid tube is inspected and surface defects are removed, cut into the required length, centered on the end face of the perforated end of the tube, and then sent to the heating furnace for heating and perforated on the perforator. While perforating, it rotates and moves forward continuously. Under the action of the rollers and the head, a cavity gradually forms inside the tube, which is called a rough tube. After the tube is removed, it is sent to the automatic tube rolling machine for further rolling, and then the wall thickness is adjusted by the leveling machine, and the diameter is determined by the sizing machine to meet the specification requirements. After hot rolling treatment, a perforation experiment should be carried out. If the perforation diameter is too large, it should be straightened and corrected, and finally labeled and put into storage.
Comparison of cold drawing process and hot rolling process: The cold rolling process is more complicated than the hot rolling process, but the surface quality, appearance, and dimensional accuracy of cold-rolled steel plates are better than those of hot-rolled plates, and the product thickness can be thinner.
Size: The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-200mm. The outer diameter of cold-rolled seamless steel pipe can be up to 6mm, the wall thickness can be up to 0.25mm, the outer diameter of thin-walled pipe can be up to 5mm, and the wall thickness is less than 0.25mm (even less than 0.2mm), and the dimensional accuracy of cold rolling is higher than that of hot rolling.
Appearance: Although the wall thickness of cold-rolled seamless steel pipe is generally smaller than that of hot-rolled seamless steel pipe, the surface looks brighter than thick-walled hot-rolled seamless steel pipe, the surface is not too rough, and the diameter does not have too many burrs.
Delivery status: Hot-rolled steel pipes are delivered in hot-rolled or heat-treated state, and cold-rolled steel pipes are delivered in heat-treated state.