宝钛集团有限公司

In order to obtain Ti542222 high strength and high toughness titanium alloy for deep-sea pressure hull with the best matching of strength-plasticity-toughness, Ti542222 titanium alloy plate with a thickness of 40 mm developed by Baoji Titanium Industry Co., Ltd. was selected as the research object in this paper. α+β→β phase transition temperature was 897 ℃. The plate was prepared by phase-inversion temperature（T β ）+（30～50） ℃ heating and the deformation was 50%～80%. At the same time, according to the heat treatment test scheme designed by AMSH 81200-H-2014 titanium and titanium alloy heat treatment specification, the solid solution system was 750～880 ℃/1.5 h air cooling（AC）. The solution aging system was 860 ℃/1.5 h AC+（550～760） ℃/4 h AC. Axiovert 200MAT metallographic microscope（OM） was used to observe the microstructure of the alloy after hot rolling and heat treatment.JSM6480 scanning electron microscope（SEM） was used to detect and analyze the microstructure and tensile fracture of the solution treatment and solution aging treatment. The effects of solution temperature and aging temperature on microstructure, mechanical properties and fracture morphology of Ti542222 titanium alloys thick plate were studied by room temperature tensile test and Charpy impact test using Instron5885 electronic universal testing machine and JNS-300 impact testing machine. The results showed that after ordinary annealing at 750～800 ℃, the alloy was composed of primary α p phase and metastable β phase, and both of them grow up with the increase of temperature. The secondary α s phase on the β matrix changes from α s to β, and with recovery and recrystallization, the strength decreased and the toughness increased. When annealed at 800～860 ℃, the primary α p phase decreased, and α″ phase precipitates on β phase matrix. With the increase of temperature, the primary α p phase and β phase gradually coarsened, and α″ phase increased greatly, then the strength increased steadily, and the plasticity and toughness decreased. In the dual annealing of 860 ℃/1.5 h AC+（550～760） ℃/4 h AC, when the low temperature annealing temperature was 550 ℃, the microstructure was basically the same as that after 860 ℃/1.5 h AC annealing. The secondary α s phase formed by the decomposition of metastable β phase was relatively small and uniform, and the strength remained high, but the toughness could not meet the needs of materials for deep-sea pressure hulls. When the low temperature annealing temperature was 630～760 ℃, the microstructure was primary α p phase, β phase and α s phase. With the increase of low temperature annealing temperature, primary α p phase gradually gathered and grew, and the thicknesses of β phase and α s phase lamellar coarsened, then the strengthening effect decreased. The toughness was significantly improved. Only when the low-temperature annealing temperature was 700 ℃, the tensile strength, the yield strength, the elongation and the impact energy would be respectively 1134 MPa, 1057 MPa, 17.5% and 48 J, which could better meet the requirements of materials for deepsea pressure hulls. Therefore, the heat treatment system for determining the best strength-plastic-ductility matching of Ti542222 titanium alloy for deep-sea pressure shell was（860 ℃/1.5 h AC）+（700 ℃/4 h AC）. The successful development of high strength and high toughness Ti542222 titanium alloy had broad application prospects. It could not only meet the needs of deep-sea pressure hull, but also be used in submarines, unmanned submarines, surface ships, deep-sea space stations and other marine engineering equipment and aviation, aerospace and other fields.