Large diameter straight welded pipe cooling process

　　The magnitude of the tissue stress is related to the cooling rate, shape, and chemical composition of the workpiece in the martensitic transformation zone. The faster the cooling rate, the higher the carbon content and alloy composition, the greater the uneven plastic deformation caused by thermal stress during cooling, and the greater the residual stress formed.

　　On the other hand, in the process of heat treatment, when steel changes to austenite to martensite, the increase of specific volume is accompanied by the expansion of the volume of the workpiece, and the parts of the workpiece are successively transformed, resulting in inconsistent volume growth and tissue formation. stress. The final result of the change in tissue stress is the tensile stress on the surface layer and the compressive stress on the core, just opposite to the thermal stress.

　　When the large-diameter straight-welded welded pipe is finished at the end of cooling, the core portion of the surface is not pulled freely due to the contraction of the final cooling volume of the core. That is, under the action of thermal stress, the surface of the workpiece is finally pressed and the core is pulled. This phenomenon is affected by factors such as cooling rate, material composition and heat treatment proc.

　　http://www.xysteelpipe.com/info/Large-diameter-straight-welded-pipe-cooling-process-1263-1.htm

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