What is the difference between hot-rolled seamless steel tube and cold-rolled seamless steel tube?

- Oct 31, 2019-

Difference between hot rolled seamless steel tube and cold rolled seamless steel tube:
     1) cold rolled seamless steel pipe is usually small diameter, while hot-rolled seamless steel pipe is usually large diameter.
     2) the precision of cold-rolled seamless steel tube is higher than that of hot-rolled seamless steel tube, and the price is also higher than that of hot-rolled seamless steel tube.
     3) hot rolled seamless pipe is divided into general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, oil cracking pipe, geological steel pipe and other steel pipes.
     4) cold rolled (drawn) seamless steel pipe includes general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe and other steel pipes, as well as carbon thin-walled steel pipe, alloy thin-walled steel pipe, stainless thin-walled steel pipe and special-shaped steel pipe.

technological process:
         Sizing (or reducing) → cooling → blank pipe → straightening → hydrostatic test (or flaw detection) → marking → warehousing.
         Cold drawing (rolling) seamless steel pipe: round tube blank → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi pass cold drawing (cold rolling) → blank tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → warehousing.
Hot rolling is relative to cold rolling, cold rolling is rolling under recrystallization temperature, and hot rolling is rolling above recrystallization temperature.

Hot-rolled seamless tube:

Advantages:

        It can destroy the cast structure of steel ingot, refine the grain of steel and eliminate the defects of microstructure, so that the microstructure is compacted and the mechanical properties are improved.The improvement is mainly reflected in the direction of rolling so that the steel is no longer isotropic to some extent.The bubbles, cracks and looseness formed during pouring can also be welded under high temperature and 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 layered.The tensile properties of the steel along the thickness are greatly deteriorated by the layering, and interlaminar tears may occur during weld shrinkage.The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than the strain induced by load.

       2. Residual stress caused by uneven cooling.Residual stress is the internal self-balancing stress without external force. All kinds of hot-rolled sections have this kind of residual stress.Although the residual stress is self-balanced, it has some influence on the performance of steel member under the action of external force.Such as deformation, stability, anti - fatigue and other aspects may have adverse effects.

       3. Hot rolled steel products are difficult to control in terms of thickness and edge width.We are familiar with thermal expansion and contraction, because at the beginning of hot rolling, even if the length and thickness are up to the standard, there will still be a certain negative difference after cooling, the wider the negative difference edge is, the thicker the thickness is, the more obvious.Therefore, for large steel, the steel side width, thickness, length, Angle, and edge can not be too accurate.

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