Seamless steel pipes are generally made by hot rolling or cold rolling of high quality carbon-bonded steel 16Mn, 5MnV or alloy steel 40Cr, 30CrMnSi, 45Mn2, 40MnB etc. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid conveying pipes. Seamless tubes made of medium carbon steel, such as 45, 40Cr, are used to manufacture mechanical parts, such as stress parts of automobiles and tractors. Generally, seamless steel tube should be used to ensure strength and flattening test.
Seamless steel pipes can be divided into hot-rolled and cold-rolled seamless steel pipes: hot-rolled steel pipes are delivered in hot-rolled or heat-treated state; cold-rolled steel pipes are delivered in heat-treated state.
Cold rolled seamless steel pipes are divided into general steel pipes, low medium pressure boiler tubes, high pressure boiler tubes, alloy steel pipes, stainless steel pipes, oil cracking pipes and other steel pipes. They also include carbon thin-walled steel tubes, alloy thin-wall steel tubes, stainless steel thin walled steel tubes, and special-shaped steel tubes. The outer diameter of hot rolled seamless pipe is generally larger than 32mm and the wall thickness is 2.5-75mm. The cold-rolled seamless steel pipe diameter can reach 6mm, the wall thickness can reach 0.25mm, the outer diameter of the thin-walled tube can reach 5mm, the wall thickness is less than 0.25mm, and the cold rolling ratio is higher than the hot rolling dimension accuracy.
Hot rolled seamless steel tubes are divided into general steel pipes, low and medium pressure boiler tubes, high pressure boiler tubes, alloy steel tubes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.
The main differences between hot rolled and cold rolled seamless steel tubes are:
1. The local section of the permitted section of cold-rolled steel can be partially buckled, which can make full use of the post buckling capacity of the rod.
2. The cause of residual stress of hot rolled and cold rolled steel is different, so the distribution of cross section is also very different. The distribution of residual stresses on cold-formed thin-walled steel sections is curved, while the residual stress distribution on hot rolled steel or welded steel sections is thin film type.
3. The free torsion stiffness of hot-rolled steel is higher than that of cold rolled steel, so the torsion resistance of hot-rolled steel is better than that of cold rolled steel.
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