Research On Forging-free Direct Rolling Mechanism And Hot Rolling Process Of TA1 Large Ingot Cast By Single EB Furnac

Industrial pure titanium plates/strips have good mechanical properties,excellent corrosion resistance,and weldability,which is widely used in fields such as ocean engineering,seawater desalination,chemical engineering,metallurgy,and power,and the demand of industrial pure titanium plates/strips is growing day by day.Yunnan Titanium Industry Co.,Ltd.,in collaboration with Kunming University of Science and Technology,have developed a short process preparation method that uses an electron beam cold bed furnace to melt and cast pure titanium flat ingots,directly hot rolling the flat ingots into titanium coils.By shortening the process flow,improving the yield rate,and reducing the production cost of titanium strips.But the microstructure of TA1 ingots cast in EB furnace is extremely coarse(with grain size reaching centimeter level).There are currently few reports on how the coarse structure in the cast state can be broken and refined to micrometer level during plastic deformation to obtain excellent mechanical properties.Therefore,in this paper,a single EB furnace melt-cast TA1 pure titanium flat ingot of 1570 mm wide x 200 mm thick x 8000 mm long was sampled in the rolling direction and then subjected to a multi-pass reduced temperature thermal deformation experiment with a total deformation of 75% at a deformation temperature of 860°C to 920°C and a strain rate of 10s-1 using a Gleeble-1500 thermal simulation tester to simulate its plate /strip rough rolling process and conduct a comprehensive analysis of the experimental rolling.Through the study of the thermal deformation behaviour,microstructure,structure and mechanical properties of large ingot billets of TA1 melted in a single EB furnace under different process parameters,the following conclusions were obtained:The as-cast structure of the single EB furnace molten TA1 large ingot billet is coarse equiaxed and columnar with an average grain size of 3.5 cm and a relatively homogeneous tissue distribution..The flow stress curves of different parts of TA1 undergoe process hardening and dynamic softening at deformation temperature of860℃～920℃,and the flow stress gradually decreases with the increase of initial compression temperature;After 5 passes of compression,the coarse as-cast microstructure of TA1 ingot is broken and refined,resulting in incomplete recrystallization α In terms of phase structure,the average grain size decreases from centimeter level to micrometer level,and the preferred orientation of the grains first decreases and then slightly increases.According to the results of multi-pass temperature reduction thermal deformation behavior,microstructure,texture,and substructure evolution,it can be seen that under different deformation temperature conditions,the single EB furnace melt-cast TA1 ingot billets are mainly refined by discontinuous dynamic recrystallisation during the noforging direct rolling process,with the grain boundaries bowing out of nucleation,consuming distortion energy and forming new distortion-free grains to replace the original ones.The new distortion-free grains replace the original deformed structure.Based on the simulation results of multi pass temperature reduction thermal deformation,the hot rolling process of TA1 pure titanium ingot was studied.After rough rolling at a deformation temperature of 860℃～920℃,the TA1 ingot billets undergo dynamic recrystallisation.As the initial rolling temperature increased,the degree of recrystallization gradually increases,and the average grain size after crystallization also increases.The mechanical properties of the plate are related to the degree of recrystallization and grain size,with the best overall mechanical properties at an initial rolling temperature of 890°C.The average grain size and mechanical properties of the deformed slabs are similar after rolling at 890°C.After further finishing,the organization and mechanical properties of the slabs in different parts are more uniform at an initial rolling temperature of 890°C.According to the evolution results of microstructure and mechanical properties during rough rolling and finishing rolling,it can be seen that after hot rolling at an initial rolling temperature of 890℃,the recrystallization degree and grain size of of TA1 plates are moderate and the mechanical properties are more excellent,.with an average grain size of 22.2±0.5μm,tensile strength of 375±3 MPa,yield strength of 316±5 MPa and elongation after break of 33.1%±1.6%.The elongation after break was 33.1%±1.6%..Comprehensive analysis show that the as-cast microstructure of TA1 large ingots cast in a single EB furnace is uniform.When hot compression is carried out at different parts at an initial deformation temperature of 860℃～920℃,the microstructure refinement mechanism of straight rolling without forging is discontinuous dynamic recrystallization,and the microstructure is more uniform at deformation temperatures of890℃ and 920℃;When the deformation temperature is 890℃,the microstructure and comprehensive mechanical properties of different parts of the plate are the best,which is suitable for hot processing.