Hot rolling and cold rolling technology of seamless steel tube

Seamless steel pipes are made of steel ingots or solid tube billets through the perforation into capillary tubes and then made by hot rolling, cold rolling, or cold drawing. The specifications of seamless steel pipes are expressed in millimeters of outer diameter * wall thickness. Seamless steel pipes are divided into two types: hot-rolled and cold-rolled (dial) seamless steel pipes.

The process flow of seamless steel pipe: round tube billet → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → pipe removal → sizing (or reducing) → cooling → straightening → hydraulic test (or flaw detection) → Mark → Warehousing

Hot-rolled seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes, and other steel pipes. Cold-rolled (dial) seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, and other steel pipes, as well as carbon thin-walled steel pipes, alloy thin-walled steel pipes, Stainless thin-walled steel pipes, special-shaped steel pipes. The outer diameter of the hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-75mm. The diameter of the cold-rolled seamless pipe can be up to 6mm, the wall thickness can be up to 0.25mm, and the outer diameter of the thin-walled pipe can be up to 5mm and the wall thickness is less than 0.25mm. Rolling has higher dimensional accuracy than hot rolling.

Hot rolling, as the name implies, the temperature of the rolled piece is high, so the deformation resistance is small, and a large amount of deformation can be achieved. Taking the rolling of steel plate as an example, the thickness of the continuous casting billet is generally about 230mm, and after rough rolling and finishing rolling, the final thickness is 1-20mm. At the same time, due to the small width-to-thickness ratio of the steel plate, the dimensional accuracy requirements are relatively low, and the shape problem is not prone to occur, and the crown is mainly controlled. The requirements for the organization are generally achieved through controlled rolling and cooling, that is, controlling the start-rolling temperature and final rolling temperature of finishing rolling.

Generally, seamless steel pipes are made of 10, 20, 30, 35, 45, and other high-quality carbon steels such as 16Mn, 5MnV, and other low-alloy structural steels or 40Cr, 30CrMnSi, 45Mn2, 40MnB, and other composite steels by hot rolling or cold rolling. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid transportation pipelines. Seamless pipes made of medium carbon steel such as 45 and 40Cr are used to manufacture mechanical parts, such as the stressed parts of automobiles and tractors. Generally, seamless steel pipes must be used for strength and flattening tests. Hot-rolled steel pipes are delivered in the hot-rolled state or heat-treated state; cold-rolled steel pipes are delivered in the hot-heated state.