Study On Short Process Preparation And Heat Treatment Process Of TA31 Titanium Alloy Seamless Tube

Ti-6Al-3Nb-2Zr-1Mo(TA31)titanium alloy,which is a near?-type titanium alloy.It has high strength,plasticity and corrosion resistance,especially high fracture toughness,stress corrosion fracture toughness,impact toughness and weldability.Its pipes,plates and profiles have a wide range of applications in the field of marine engineering.The traditional TA31 alloy seamless pipe preparation process mainly uses TA31 alloy ingots melted by VAR for at least three times.After forging,the finished seamless pipe is prepared by rolling,drawing,spinning and other methods.However,the preparation process has the problems of long preparation cycle,complicated forming process,low yield rate,etc.,which greatly increases the preparation cost of TA31 alloy seamless pipe and limits the wide application of its alloy seamless pipe.Based on the above reasons,this article proposes a high-efficiency and short-flow preparation proce ss to shorten the process flow and reduce the preparation cost.First,the raw materials are alloyed by VAR furnace melting technology,and then remelted in an electron beam cooling bed melting furnace(EB)to directly obtain TA31 alloy ingots.After that,the TA31 alloy seamless tube is obtained by directly performing cross-rolling and piercing without forging.This paper analyzes the composition and thermal deformation behavior of TA31 alloy melted by VAR+EB,and at the same time obtains seamless tube of TA31 alloy after forging-free straight rolling.The seamless pipe was annealed,and the effect of annealing temperature on the structure and mechanical properties of the seamless pipe was studied.The following conclusions were obtained:The TA31 alloy ingots smelted by VAR+EB,the composition of each element meets the requirements of the national standard GB/T 3620.1-2016,and the distribution of the elements is uniform,and the ingot structure is a uniform Widmanstatten structure.The flow stress of the a lloy under deformation parameters was obtained through the study of thermal deformation behavior,and then the constitutive equation of VAR+EB smelting TA31 alloy ingot was established.The thermal activation energy of the material was 790.478k J/mol and th e thermodynamic index was 4.070..According to the thermal processing map when?=0.6 established by the dissipation judgment criterion of the DMM model and the Prasad instability criterion,the instability zone of the ingot is the low temperature and high strain zone,and the processing safety zone of the ingot is the high temperature and high strain zone.In the TA31 alloy seamless pipe prepared by a short process,the structure of the rolled seamless pipe is a deformed Widmanstatten structure,which has o bvious processing flow lines and uneven structure.The average value of its mechanical properties is R_m=854MPa,R_p0.2=730MPa and A=10%.The seamless tube is annealed at 800?950?.With the increase of annealing temperature,the structure gradually becomes uniform,and the crystal grains gradually shift from?01 0?to?0001?.The preferred orientation of the grains first weakens,then increases,and then gradually weak ens.When the annealing temperature reaches 900°C,the TA31 alloy seamless tube has good comprehensive mechanical properties,the lamellar primary?phase and the original?phase grain boundaries disappear,and the structure is very uniform.The grains hav e a strong preferential orientation in the direction close to<0001>,and the average mechanical properties are R_m=873MPa,R_p0.2=785MPa and A=12.8%.At this time,the mechanical properties of the TA31 alloy seamless pipe have reached the mechanical propert ies of the TA31 alloy seamless pipe obtained by the traditional process.In summary,it is shown that the TA31 alloy seamless pipe obtained by the short-flow seamless pipe preparation process can reach the mechanical properties of the seamless pipe obtaine d by the traditional process.Compared with the traditional process,it has the advantages of short molding cycle,simple process flow,high yield rate,etc.,which greatly reduces the preparation cost of alloy seamless pipes to promote the wide applicatio n of TA31 alloy seamless pipes.