The difference between hot-rolled seamless steel pipe and cold-rolled seamless steel pipe

In terms of processing technology: hot rolling is hot processing, and cold drawing is cold processing. Hot rolling is rolling above the recrystallization temperature, and cold rolling is rolling below the recrystallization temperature;

Distinguish from appearance: cold-rolled seamless steel pipes have a bright surface and smaller diameters than hot-rolled seamless steel pipes. The diameter of hot-rolled seamless steel pipes is larger than that of cold-rolled seamless steel pipes, and there is obvious oxide scale or red rust on the surface;

In terms of accuracy: the accuracy of cold-rolled seamless steel pipes is higher than that of hot-rolled seamless steel pipes, and the price is also higher than that of hot-rolled seamless steel pipes.

Distinguished by use: hot-rolled steel pipes are used in fluid transportation, mechanical structures, and other situations where size requirements are not high, while cold-rolled steel pipes are used in precision instruments, hydraulic systems, pneumatics, and other places with high requirements. In terms of wall thickness, cold-drawn seamless pipes are more uniform than hot-rolled seamless pipes.

Advantages and disadvantages of hot-rolled seamless pipes: The advantage is that hot rolling can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate defects in the microstructure, thereby making the steel structure dense and improving its mechanical properties. The disadvantage is that ①The tensile performance of the steel along the thickness direction has greatly deteriorated, and interlayer tearing may occur when the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by the load; ②Residual stress caused by uneven cooling. It may have adverse effects on deformation, stability, fatigue resistance, etc.

Process flow:

Hot rolling (extruded seamless steel pipe): round tube blank → heating → perforation → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → billet tube → straightening → hydraulic pressure Test (or flaw detection) → Mark → Warehouse.

Cold drawn (rolled) seamless steel pipe: round tube blank → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → Hydrostatic test (flaw detection)→marking→warehousing.