(1) after hot rolling, the inside of the SPA - H non-metallic inclusions (mainly sulfide and oxide and silicate) was pressed into thin slices, appear statified phenomenon (sandwich). Layered make SPA - H plate along the thickness direction tensile performance is much worse, and may in the weld shrinkage occurs when torn between the layers. Weld shrinkage induced local strain often reach the yield point several times as much, much bigger than the load caused by the strain.
(2) the residual stress caused by uneven cooling. Residual stress is without external force within the phase equilibrium under the action of stress and all sorts of cross section of hot-rolled SPA - H steel has this kind of residual stress, the general SPA - h-beam section size, the greater the residual stress. Although the residual stress is the phase equilibrium, but the action of external force of SPA - H steel component performance still has certain influence. Such as the deformation, stability, fatigue resistance, etc, are likely to produce adverse effect.
(3) hot rolling can not very precise control of SPA - H the required mechanical properties, microstructure and mechanical properties of hot rolled products can't be smooth. Its strength index under cold work hardening of the products, and higher than the full annealing products, plastic index higher than that of cold work hardening of the products, and less than full annealing products.
(4) the thickness of hot rolled SPA - H size are difficult to control, control accuracy is relatively poor; Cold-rolled products from the hot SPA - H surface roughness Ra value is in commonly 0.5 ~ 1.5 microns. Therefore, the cold rolling process of hot rolled SPA - H as much as blank.
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