Difference between cold rolling and hot rolling of seamless steel pipe
Seamless steel pipe can be divided into hot rolling and cold drawing according to production methods. What’s the difference between them?
1. Different classification
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.
Cold rolled seamless steel 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, 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.
2. Different process flow:
Hot rolling seamless steel tube round billet → heating → piercing → three roll cross rolling, continuous rolling or extrusion → pipe stripping → sizing → cooling → billet pipe → straightening → hydrostatic test → marking → warehousing.
Seamless steel tube round billet → heating → piercing → heading → annealing → pickling → oiling → multi pass cold drawing → billet tube → heat treatment → straightening → hydrostatic test → marking → warehousing.
After hot rolling, the non-metallic inclusions (mainly sulfide and oxide, and silicate) in the steel are pressed into thin sheets,and delamination (interlayer) occurs. Delamination makes the tensile properties of the steel along the thickness direction deteriorate greatly,and it is possible that the interlaminar tear occurs when the weld shrinks.The local strain induced by weld shrinkage is often several times of the yield point strain,which is much larger than that caused by load.
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