Seamless steel pipes are divided into hot rolled and cold rolled (drawn) seamless steel pipes.
Cold-rolled seamless steel pipes:
Cold-rolled seamless pipes are used for mechanical structure, hydraulic equipment with high dimensional accuracy and good surface finish.
In addition to general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, also includes thin-wall carbon steel pipes,thin-wall alloyed steel pipes, thin-wall stainless steel pipes, special-shaped steel pipes.The outer diameter of hot-rolled seamless pipes is generally bigger than 32mm, the wall thickness is 2.5-75mm, the diameter of cold-rolled seamless 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, the wall thickness is less than 0.25mm, and the dimension precision of cold-rolled pipe is higher than hot-rolled pipe.
Hot rolled seamless steel pipes:
Hot rolled seamless steel pipes are divided into general steel pipes, low and medium pressure boiler tubes, high pressure boiler tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, geological steel tubes and other steel tubes.
General seamless tube: it is made of high quality carbon bonded steel such as 10,20, 30, 35 and 45. 16Mn, 5MwV and other low alloy structural steel, or alloy steel such as 40Cr, 30CiMnSi, 4512 and 40MnB. Hot rolled or cold rolled 10, 20 and other low carbon steel manufacturing seamless pipes are mainly used for fluid transport pipelines.Seamless pipes made of medium carbon steel such as 45 and 40Cr are used to make mechanical parts, such as stressed parts for cars and tractors.We need to ensure the strength and flattening test of generally used seamless steel tubes .Hot rolled steel tubes are delivered in hot rolled or heat treated state.Cold rolled steel pipes are delivered in heat treatment condition.
Main differences between hot rolled and cold rolled seamless tubes:
- Local buckling is allowed in the section of cold-rolled steel pipes, which can make full use of the bearing capacity of the pipes after buckling;However, local buckling of section is not allowed in hot rolled section.
- The causes of residual stress of hot rolled section and cold rolled section are different, so the distribution on the section is also very different.The residual stress distribution on the section of cold-formed thin-walled steel is of bending type, while that on the section of hot-formed steel or welded steel is of thin film type.
- The free torsional stiffness of hot-rolled sections is higher than that of cold-rolled sections, so the torsional resistance of hot-rolled sections is better than that of cold-rolled sections.
Cold rolled seamless tube is at room temperature, after cold drawing, cold bending and other cold processing,making steel plate or steel strip into a variety of steel tubes.
Advantages of cold rolled seamless steel pipes:
Fast molding speed, high yield, and no damage to the coating, can be made into a variety of cross section forms, to meet the needs of the use conditions;Cold rolling can produce a lot of plastic deformation of steel, thus increasing the yield point of steel.
Advantages of hot-rolled seamless steel pipes:
Compared with the cold rolled seamless tube, which is rolled below the recrystallization temperature,the hot rolled seamless tube is rolled above the recrystallization temperature. It can destroy the casting structure of steel ingot, refine the grain of steel, and eliminate the defects of microstructure, so that the microstructure of steel can be compactness and mechanical properties can be improved.This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to some extent.Bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.