What are the differences between hot-rolled and cold-rolled seamless steel pipes?

What are the differences between hot-rolled seamless steel pipes and cold-rolled seamless steel pipes? Are common seamless steel pipes hot-rolled seamless steel pipes? Cold-rolled seamless steel pipes are often small-diameter, and hot-rolled seamless steel pipes are often large-diameter. The precision 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.
Seamless steel pipes are divided into hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes due to their different manufacturing processes. Cold-drawn (rolled) pipes are divided into round pipes and special-shaped pipes.

1) Different uses

Hot-rolled seamless pipes are divided into ordinary steel pipes, medium and low pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes. Cold-rolled (pulled) seamless steel pipes are divided into ordinary steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes and other steel pipes, as well as carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless steel thin-walled steel pipes, and special-shaped steel pipes.

2) Different sizes

The outer diameter of hot-rolled seamless pipes is generally greater than 32mm, and the wall thickness is 2.5-75mm. The diameter of cold-rolled seamless pipes can reach 6mm, and the wall thickness can reach 0.25mm. The outer diameter of thin-walled pipes can reach 5mm, and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling.

3) Process differences

1. Cold-rolled steel allows local buckling of the cross section, which can make full use of the bearing capacity of the steel bar after buckling; while hot-rolled steel does not allow local buckling of the cross section.

2. The reasons for the generation of residual stress in hot-rolled steel and cold-rolled steel are different, so the distribution on the cross section is also very different. The residual stress distribution of cold-bent thin-walled steel cross section is in the shape of a curve, while the residual stress distribution of hot-rolled thin-walled steel or welded steel cross section is in the shape of a film.

3. The free torsional stiffness of hot-rolled steel is higher than that of cold-rolled steel, so the torsional resistance of hot-rolled steel is better than that of cold-rolled steel.

4) Different advantages and disadvantages

Cold-rolled seamless pipe refers to steel plates or steel strips that are processed into various types of steel by cold drawing, cold bending, cold drawing and other cold processing at room temperature.

Advantages:

Fast forming speed, high output, no damage to the coating, can be made into a variety of cross-sectional forms to meet the needs of use conditions; cold rolling can cause steel to produce greater plastic deformation, thereby increasing the yield strength of the steel point.

Disadvantages:

1. Although there is no thermoplastic compression during the forming process, there is still residual stress in the cross section, which is bound to affect the overall and local buckling characteristics of the steel;

2. The style of cold-rolled steel is generally open-section, which makes the free torsional stiffness of the cross section lower. It is easy to twist when bent, and it is easy to bend and torsional buckling when under pressure, and the torsion resistance is poor;

3. The wall thickness of the cold-rolled steel plate is small, there is no thickening phenomenon at the corners of the plate joints, and the ability to withstand local concentrated loads is weak.

Hot-rolled seamless pipes are relative to cold-rolled seamless pipes. Cold-rolled seamless pipes are rolled below the recrystallization temperature, and hot-rolled seamless pipes are rolled above the recrystallization temperature.

Advantages:

It can destroy the casting structure of the steel ingot, refine the grains of the steel, eliminate microstructure defects, make the steel structure dense, and improve the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks, looseness, etc. formed during casting can also be welded under high temperature and high pressure.


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