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Difference between precision and hardness of hot-rolled and cold-drawn seamless steel tubes

Hot-rolled seamless steel pipe is divided into general steel pipe, low and medium pressure boiler seamless steel pipe, high pressure boiler seamless steel pipe, alloy seamless steel pipe, stainless seamless steel pipe, petroleum cracking pipe, geological steel pipe and other seamless Steel pipes, etc.

Cold drawn steel pipe is divided into general steel pipe, electric resistance welded pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, other seamless steel pipes, and also includes carbon thin-walled steel pipe and alloy thin-walled steel pipe. Stainless thin-walled steel pipe and special-shaped steel pipe.

Accuracy

The accuracy is different: the outer diameter of hot-rolled seamless steel pipe is generally larger than 32mm, the wall thickness is 2.5-75mm, the outer diameter of cold-drawn seamless steel pipe can be 6mm, the wall thickness can be 0.25mm, and the outer diameter of thin-walled pipe can reach 5mm. The wall thickness is less than 0.25mm, and the cold drawn seamless steel pipe has higher dimensional accuracy than the hot rolled seamless steel pipe.

This is one of the reasons why the cold drawn seamless steel pipe is more expensive than the hot rolled seamless steel pipe.

Hardness

The free torsional rigidity of the hot-rolled seamless steel pipe is higher than that of the cold-drawn seamless steel pipe, so the torsional performance of the hot-rolled steel pipe is better than that of the cold-drawn seamless steel pipe. Cold drawn seamless steel pipe is a kind of high precision precision cold drawn seamless steel pipe material after cold drawing or hot rolling.

Because the inner and outer walls of the precision cold-drawn seamless steel pipe have no oxide layer, high pressure, no leakage, high precision, high smoothness, no cold deformation, no flaring, no cracking, no cracks, etc., so it is mainly used to produce pneumatic or hydraulic components. Such as cylinders or cylinders, can be seamless tubes.

1. Annealing is to heat the precision cold drawn seamless steel pipe to the appropriate temperature, using different holding time according to the material and the work piece size, and then slowly cooling, in order to make the internal structure of the metal reach or close to equilibrium, and obtain good process performance and Use performance or prepare for further quenching.

2. Normalizing is to cool the precision cold drawn seamless steel pipe to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, but the obtained micro structure is finer, which is often used to improve the cutting performance of materials, and sometimes used for For some less demanding parts, the final heat treatment.

3. Quenching is the rapid cooling of precision cold drawn seamless steel tubes after quenching in water, oil or other inorganic salts, organic aqueous solutions and other quenching media. After quenching, the precision cold drawn seamless steel pipe becomes hard, but at the same time becomes brittle.

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