From the 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;
From the appearance: the surface of cold-rolled seamless steel pipe is bright, and the diameter is smaller than that of hot-rolled seamless steel pipe. The diameter of hot-rolled seamless steel pipe is larger than that of cold-rolled seamless steel pipe, and there is obvious oxide scale or red rust on the surface;
From the precision: the precision of cold-rolled seamless steel pipe is higher than that of hot-rolled seamless steel pipe, and the price is also higher than that of hot-rolled seamless steel pipe.
From the use: hot-rolled steel pipe is used in fluid transportation, mechanical structure, and other occasions with low size requirements and cold-rolled steel pipe is 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 the defects of the microstructure so that the steel structure is dense and the mechanical properties are improved. Disadvantages are: 1. The tensile performance of the steel along the thickness direction greatly deteriorates, 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; 2. Residual stress caused by uneven cooling. It may hurt deformation, stability, fatigue resistance, etc.
Process flow:
Hot rolling (extruded seamless steel pipe): round tube billet → heating → piercing → three-roller oblique rolling, continuous rolling or extrusion → tube removal → sizing (or reducing diameter) → cooling → billet tube → straightening → hydraulic pressure test (or flaw detection) → marking → storage.
Cold drawn (rolled) seamless steel pipe: round tube billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multiple passes of cold drawing (cold rolling) → billet tube → heat treatment → straightening → water pressure test (defect detection) → marking → storage.
Post time: Dec-24-2024