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What are the heat treatment processes for welded pipes?

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Welded steel tubes are generally formed by deforming steel strips or steel plates into round or square shapes under the action of external force, and then welding the seams on the surface to form welded steel pipes. The production process of welded steel pipe is simple, the production efficiency is high, there are many varieties and specifications, and the investment in equipment is small, but the general strength is lower than that of seamless pipe. Widely used in water supply engineering, petrochemical industry (octg pipe), chemical industry, electric power industry, agricultural irrigation, urban construction

There are many processes in the processing of welded pipes, and we need to pay attention to every detail. Welded pipes need to go through various processes before application. The heat treatment of welded steel pipes is a very important link in the processing of welded steel pipes. Thermal processing is a metal thermal processing process that first heats, heats, and cools metal materials in a certain medium, and controls its metal properties by changing the metallographic structure on the surface or inside of the material.

During the heating and cooling process of the structural welded pipe workpiece, due to the inconsistency of the cooling rate and time between the surface layer and the core, a temperature difference is formed, which will lead to uneven volume expansion and contraction and stress, that is, thermal stress. Under the action of thermal stress, since the temperature of the surface layer is lower than that of the core, the contraction is also greater than that of the core, so that the core is pulled. When the cooling is over, the surface is compressed and the core is pulled because the core cooling volume contraction cannot proceed freely. That is, under the action of thermal stress, the surface of the workpiece is compressed and the core is pulled.

This phenomenon is affected by factors such as cooling rate, material composition and heat treatment process. When the cooling rate is faster, the carbon content and alloy composition are higher, the uneven plastic deformation generated under the action of thermal stress during the cooling process is greater, and the residual stress formed is greater.

On the other hand, during the heat treatment process of steel, due to the change of the structure, that is, the transformation from austenite to martensite, the increase in specific volume will be accompanied by the expansion of the workpiece volume. Each part of the workpiece changes phase successively, resulting in inconsistent volume growth and tissue stress. The result of tissue stress changes is that the surface is subjected to tensile stress and the heart is subjected to compressive stress, which is just the opposite of thermal stress. The size of the organizational stress is related to the cooling rate, shape, chemical composition of the material and other factors of the workpiece in the martensitic transformation zone.

In order to make the welded pipe have the required mechanical properties, physical properties and chemical properties, in addition to the reasonable selection of materials and forming processes, the heat treatment process is often essential. In addition, aluminum, copper, magnesium, titanium, etc. and their alloys can also change their mechanical, physical and chemical properties through heat treatment to obtain different performance.

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