Difference between hot and cold seamless tube

Seamless steel tube has a hollow section, a large number of which are used for conveying fluid, such as crude oil, natural gas, coal gas, water and some solid materials, etc. Compared with solid round steel, when the torsional strength is same, the weight of the seamless steel pipe is relatively light, so it is a kind of economical steel, which is widely used in manufacture oil tubular goods and mechanical parts. The use of seamless steel tube can improve the utilization of materials, simplify the manufacturing process, save materials and processing time.

Generally seamless steel tubes are made by hot rolling or cold rolling with 10,20,30,35,45 high quality carbon steel and 16Mn, 5MnV low alloy structural steel or 30CrMnSi, 40Cr, 45Mn2, 40MnB alloy steel. Seamless pipe, made by 10,20 and other low carbon steel production, is mainly used for conveying pipe, while made by 45,40Cr medium carbon steel to manufacture mechanical parts. What’s the difference between hot rolled seamless steel tube and cold rolled seamless steel tube?

Cold rolling seamless tube

Cold rolled seamless tube is a seamless steel tube for high dimensional accuracy and good surface finish. Cold rolled seamless pipe in addition to include the general steel, low and medium pressure boiler tube, high-pressure boiler tubes, alloy steel pipe, stainless steel pipe and oil cracking tube, also includes carbon thin wall steel pipe, alloy thin wall steel tube, thin-walled stainless steel pipe and special-shaped steel tube. The diameter of cold rolled seamless steel pipe is 6mm, wall thickness is 0.25mm, while the diameter of thin-walled tube can be 5mm, wall thickness can less than 0.25mm. The dimensional accuracy of cold rolling is higher than that of hot rolling.

Hot rolling seamless tube

Hot rolling is relative to the cold rolling. Cold rolling carries on rolling below the temperature of recrystallization, and hot rolling is above the recrystallization temperature. Hot rolled seamless steel pipe is generally divided into low, medium, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, oil cracking pipe, geological steel pipe and other steel pipe. The outside diameter of hot rolled seamless tube is generally greater than 32mm and the wall thickness of that is 2.5-75mm.

Difference

• The cold rolled seamless tube allows local buckling, which can make full use of bending bearing capacity. While, hot rolled steel does not allow local buckling.
• The causes of residual stress are different, so the distribution of the cross section is also very different. The distribution of the residual stress on cold rolling thin wall steel is bending. However, the distribution of the residual stress on hot rolled steel is film type.
• The free torsional rigidity of hot rolled steel is higher than that of cold rolled steel. In other words, the torsion resistance of hot rolled steel is better than that of cold rolled steel.

Technological process

Hot rolled seamless steel pipe
round billet→heating→perforation→extrusion→sizing→hot rolling→cooling→straightening→hydrostatic test→signing→storage

Cold rolled seamless steel pipe
round billet→heating→perforation→annealing→pickling→annoit→cold rolling→heating→straightening→hydrostatic test→signing→storage