What is the difference between hot rolled seamless steel pipe and cold rolled seamless steel pipe? Is ordinary seamless steel pipe hot rolled seamless steel pipe?
Most cold-rolled seamless steel pipes are small-caliber, and most hot-rolled seamless steel pipes are large-caliber. The accuracy of cold rolled seamless steel pipe is higher than hot rolled seamless steel pipe, and the price is also higher than hot rolled seamless steel pipe.
Due to different production processes, seamless steel pipes are divided into hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes. Cold-drawn (rolled) pipes are divided into round pipes and special profile pipes.
1) Various uses Hot-rolled seamless pipes are divided into ordinary steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, oil cracking pipes, geological steel pipes and others. steel tubes. . Cold-rolled (dial) seamless steel pipes are divided into ordinary steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, oil cracking pipes, other steel pipes and carbon pipes. . Pipes steel double-walled, alloyed Pipes steel thin-walled, pipes steel profile.
2) The outer diameter of various sizes of hot-formed seamless pipes is usually over 32mm, and the wall thickness is 2.5-75mm. The diameter of cold rolled seamless pipe can be up to 6mm, and the wall thickness can be up to 0.25mm. The outer diameter of the thin-walled pipe can be up to 5mm, and the wall thickness is less than 0.25mm. Cold rolling has a higher dimensional accuracy than hot rolling.
3) Differences in process 1. Cold-rolled steel profile can allow local bending of the section, which can fully utilize the bearing capacity of the bent steel bar, while hot-rolled steel profile does not allow local bulging of the section. .
2. The reasons for the occurrence of residual stresses in hot-rolled and cold-rolled products are different, so the distribution over the section is also very different. The distribution of residual stresses in the cross section of cold-formed thin-walled steel is curvilinear, and the distribution of residual stresses in the cross section of hot-rolled or welded steel is film-like.
3. The free torsional rigidity of hot-rolled steel is higher than that of cold-rolled steel, so the torsional performance of hot-rolled steel is better than that of cold-rolled steel.
4) Various Advantages and Disadvantages Cold rolled seamless pipes are steel sheets or steel strips that are processed into various types of steel by cold drawing, cold bending, cold drawing, etc. at room temperature.
Advantages: fast molding speed, high productivity, no damage to the coating, the ability to produce various cross-sectional shapes according to the needs of the conditions of use; cold rolling can cause a large plastic deformation of the steel, thereby increasing the yield strength. steel.
Disadvantages: 1. Although there is no thermoplastic contraction during the forming process, there are still residual stresses in the section, which inevitably affect the general and local buckling characteristics of the steel 2. The style of cold rolled steel is generally open section, which makes the rigidity of the section to free torsion relatively low. It is easy to twist in bending, easy to bend and bend in compression, and has poor torsional resistance 3. The wall thickness of cold rolled steel sheets is small, and the joint angles of the sheets are not thickened, so the ability to withstand local concentrated loads is weak.
Hot rolled seamless pipes are cold rolled seamless pipes. Cold-rolled seamless pipes are rolled below the recrystallization temperature, while hot-rolled seamless pipes are rolled above the recrystallization temperature.
Advantages: It can destroy the casting structure of the steel ingot, refine the steel grains, eliminate structural defects, make the steel structure compact, and improve the mechanical properties. This improvement is mainly reflected in the direction of rolling, so that the steel ceases to be isotropic to a certain extent; bubbles, cracks and friability generated during casting can also be welded at high temperature and high pressure.
Disadvantages: 1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets and delaminate (interlayer). The delamination significantly degrades the tensile properties of the steel in the thickness direction, and an interlaminar fracture may occur when the weld shrinks. The local deformation caused by the shrinkage of the weld often reaches several times the yield strength deformation, which is much greater than the deformation caused by the load;
2. Residual stress caused by uneven cooling. Residual stress is an internal self-balancing stress without external force. This residual stress exists in hot-rolled steel sections of various cross sections. As a rule, the larger the cross section of the steel profile, the greater the residual stress. Although the residual stress is self-balancing, it still has a certain effect on the performance of steel components under the action of an external force. For example, it can adversely affect deformation, stability, and fatigue resistance.
3. It is not easy to control the thickness and side width of hot rolled steel. We are familiar with thermal expansion and contraction. Because at the beginning, even if the length and thickness are in line with the standard, there will be a certain negative difference after the final cooling. The larger the negative difference, the thicker the thickness and the more obvious the performance.
Post time: Jan-02-2023