In terms of processing technology, hot rolling is hot working, cold drawing is cold working. Hot rolling is carried out at temperatures above recrystallization temperature, and cold rolling is rolled below the recrystallization temperature.
Distinguish from appearance: cold-rolled seamless steel tube has bright surface and smaller caliber than hot-rolled seamless steel tube. The caliber of hot-rolled seamless steel tube is much larger than that of cold rolled seamless steel tube, with obvious oxide scale or red rust on the surface.
In terms of accuracy, the accuracy of cold-rolled seamless steel tubes is higher than that of hot-rolled seamless steel tubes, and the price is higher than that of hot-rolled seamless steel tubes.
From the use of the distinction: hot-rolled steel pipe used in fluid transport, mechanical structure, such as the size requirements are not high, cold-rolled steel pipe used in precision instruments, hydraulic systems, pneumatic ... and other places where the requirements are high. The cold-drawn seamless tube is more uniform than the hot-rolled seamless tube in terms of wall thickness.
Finish Rolled Seamless Steel Pipe
Advantages and disadvantages of hot-rolled seamless pipe: The advantage is that hot-rolled steel can destroy the casting structure of ingot, refine the grain size of steel and eliminate the defects of microstructure, so that the structure of steel is compact and the mechanical properties are improved. The drawbacks are as follows: 1. The tensile properties of steel along the thickness direction are greatly deteriorated, and interlayer tearing may occur when the weld shrinks. Local strain induced by weld shrinkage often reaches several times of yield point strain, which is much larger than that caused by load. 2. Residual stress caused by uneven cooling. It may have adverse effects on deformation, stability and fatigue resistance.
Large caliber hot rolled seamless steel tube
Hot rolling (extruded seamless steel pipe): round tube billet, heating, piercing, three roll skew rolling, continuous rolling or extrusion, tube drawing, sizing (or reducing diameter), cooling to blank tube to straightening, water pressure test (or flaw detection), marking, storage.
Cold drawn (rolled) seamless steel tube: round tube billet, heating, piercing, heading to annealing, acid pickling, oiling (copper plating), multi pass cold drawing (Leng Zha), blank tube to heat treatment, straightening, water pressure test (flaw detection), marking, storage.
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