There are many processes in the processing of welded square pipes, and we need to pay attention to every detail. You can learn about the heat treatment of high-frequency welded square pipes during processing as follows:
Square tubes need to go through various processes before application. The heat treatment of square tubes is a very important link in the processing of welded steel pipes. Thermal processing is a metal thermal processing process that first places metal materials in a certain medium for heating, insulation, and cooling, and controls its metal properties by changing the surface or internal metallographic structure of the material. During the heating and cooling process of the structural high-frequency welded pipe workpiece, due to the inconsistent cooling speed and time between the surface layer and the core, a temperature difference is formed, which will lead to uneven volume expansion and contraction and generate stress, that is, thermal stress.
Under the action of thermal stress, since the initial temperature of the surface layer is lower than that of the core, the shrinkage is also greater than that of the core, causing the core to be stretched. When the cooling is completed, the cooling volume shrinkage of the core cannot proceed freely, causing the surface to be compressed and the core to be stressed. pull. That is, under the action of thermal stress, the surface layer of the workpiece is compressed and the core is stretched.
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 larger, and the residual stress formed is larger. On the other hand, due to the change of the structure of steel during the heat treatment process, that is, when austenite transforms into martensite, the increase in specific volume will be accompanied by the expansion of the volume of the workpiece, and various parts of the workpiece will undergo phase transformation, resulting in inconsistent volume growth and the formation of structures. stress.
The result of tissue stress changes is that the surface layer is subject to tensile stress and the core is subject to compressive stress, which is exactly the opposite of thermal stress. The size of the structural stress is related to the cooling rate, shape, chemical composition of the material and other factors of the workpiece in the martensitic transformation zone.
