Grain Refining and Texture Control of Nonferrous Metals through High Speed Hot Rolling

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The effects of hot rolling condition on the structure of quenched sheet of Ti-6Al-4V alloy, Ti-15V-3Cr-3Sn-3Al alloy and oxygen free copper are investigated. In high speed hot rolling of Ti6Al-4V sheet, shear deformation produces a severely sheared region beneath the surface. The shear strain increases with increasing rolling temperature and decreases with reducing friction coefficient at the roll surface. Extremely fine recrystallized equiaxed alpha-grains appear in the severely sheared region of the sheet rolled in alpha + beta region. These fine alpha grains grows to diameter of 3mum on annealing at 1173K for 3.6ks. In the severely sheared region of the sheet rolled at beta region, extremely fine acicular alpha'-martensite transformed from fine recrystallized beta grains appears, which does not form equiaxed structure after annealing. In the central layer of the sheet where shear strain is negligibly small, lamellar structure develops. The preferred orientation of alpha phase in the … More severely sheared region changes with rolling temperature. In the sheet rolled at 1323K(beta region), only the transformed texture from (110)<001> orientation through the Burgers' relation, which is the shear texture of bcc metals known as Goss texture. In the severely sheared region of the sheet rolled in alpha + beta region, the texture consists of main components of transformed texture from shear texture of beta-phase and shear texture of alpha-phase (<0001>*ND). The intensity of the shear texture of the sheet rolled in alpha + beta region is weaker than that of the sheet rolled in beta region. After annealing, intensity of shear texture increases and T-texture(<0001>*TD) develops. In hot rolling of Ti-15V-3Cr-3Sn-3Al sheet, shear deformation also accumulates beneath the surface to form severely sheared region and a band of extremely fine recrystallized grains appears. The average grain size of recrystallized grains decreases with decreasing rolling temperature and with decreasing holding time af ter rolling. Grain size is 3mum after hot rolling and grows to 10mum on anneal ing af ter cold rolling. The microstructure of the copper sheet quenched immediately after high speed hot rolling changes from wrought grains to recrystallized grains with increasing rolling temperature and reduction. From the optical and TEM micrographs, it is concluded that static recrystallization occurs within very short interval after hot rolling. Less