1. Cold-rolled formed steel allows local buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; while hot-rolled steel does not allow local buckling of the section.
2. Hot-rolled steel and cold-rolled steel have different causes of residual stress, so the distribution on the cross section is also very different. The residual stress distribution on the cross-section of cold-formed thin-walled steel is curved, while the residual stress distribution on the cross-section of hot-rolled or welded steel is thin-film.
There is not much difference between the two steel pipes in the finished product, and they are generally manufactured according to standards. There is no difference in mechanical properties.
Most of the existing ones are different processing techniques and different final precisions. Generally speaking, the cold-drawn dimensional accuracy and surface finish are higher.
Hot rolling process: tube billet---heating---piercing---rolling tube---sizing---cooling bed---straightening---cutting tube---inspection---packing--- Ship
Cold drawing process: tube blank --- heating --- piercing --- hot rolling (second wear), etc. --- heading - pickling - phosphating - cold drawing - annealing (multiple passes can be repeated (From head to post process)---Straightening----Cutting---Inspection---Packing---Delivery
As an important part of steel products, steel pipes are divided into two categories: seamless steel pipes (round billets) and welded steel pipes (plates, strip billets) due to their different manufacturing processes and different shapes of billets.
(1) Seamless steel pipe
Because of their different manufacturing processes, they are divided into two types: hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes. Cold drawn (rolled) tubes are divided into round tubes and special-shaped tubes.
a. Process overview
Hot rolling (extruded seamless steel pipe): round tube billet → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or reducing) → cooling → billet tube → straightening → water pressure Test (or flaw detection) → mark → warehousing.
Cold drawn (rolled) seamless steel pipe: round tube billet → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → Hydraulic test (flaw detection) → mark → warehousing.