The long mandrels produced by method of rolling on special mills are used for tube production at continuous, three-high and other mills. Taking into account the high cost and complicated production of this kind of tools the strength increasing resulting in cutting of product cost becomes of the paramount importance. During the process of rolling the mandrel is influenced by the usual compression stresses from the rolls side, longitudinal tensile stresses from friction forces and thermocycling stresses caused by heating and cooling of mandrel's surface. Besides the misalignment of adjacent stands causes sign-variable mandrel curve and as the result its surface layers are undergone to additional stresses. During the contact of the mandrel with the heated metal comparatively thin surface layer of the mandrel is heated and resulted in its weakening. The influence of tensile stresses on the weakened surface results in reducing of resistance to the thermal fatigue and cracks formation in the first place on those mandrels' parts which are working at the most loaded stands.
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