Effect Of Heat Treatment On Microstructure And Properties Of Ti-Al-V-Mo-Zr Titanium Alloy Drill Pipe

The Ti-Al-Mo-V-Zr titanium alloy drill pipe selected in this paper is the pipe after forging,rolling and extrusion.The final formed structure is the original structure,and its structure type is lamellar.The purpose of this paper is to study the changes of microstructure and mechanical properties of titanium alloy in the process of annealing,solution aging and multiple solution aging heat treatment,and find the best heat treatment process with matching strength and toughness,so as to improve the service level of titanium alloy drill pipe in harsh oil and gas well environment.Finally,the physical performance of Ti-Al-Mo-V-Zr titanium alloy drill pipe is evaluated.(1)Compared with 980?and 1000?annealing,it is found that with the increase of temperature,the size and length of?phase in widmanstatten become wider and larger,the strength of the alloy decreases,and the plasticity and toughness increase.However,compared with the process of 1000?/1h/FC?600?/AC,it is found that the strength increases when annealing starts from 1000?,which is mainly related to the faster cooling rate of 600?air cooling in the second stage.At this time,the widmanstatten structure is more fine and dense,the grains are finer,and the strength increases.It is also found that the double annealing process from 980?/1h/FC?920?/1h/FC can greatly improve the plasticity of titanium alloy,and the yield plateau of tensile curve is increased by 53%.(2)Through(850?/900?/950?)/1h/AC+650?/6h/AC solution aging process,it is found that the strength is significantly higher than that of annealing,and below the transformation point,with the increase of temperature,the strength first decreases and then increases,mainly due to the recrystallization phenomenon at 900?and the decrease of grain size.The results show that the strength and impact energy of 1000?/1h/FC?600?/1h/AC+550?/6h/AC are higher than those of the first three groups.The analysis shows that the microstructure of the former three processes is similar to the two-state structure,and the latter is widmanstatten structure,so the impact power is high,and the aging temperature is low,there are more dispersed phase precipitation,which improves the strength.The yield strength of 1000?/1h/FC?600?/1h/AC+550?/6h/AC process reaches 931MPa,which meets the mechanical property requirements of S135 steel drill pipe.The strength toughness matching of multiple solution is lower than that of solution aging.(3)It is found that the yield strength and tensile strength of Ti-Al-Mo-V-Zr drill pipe material decrease with the increase of tensile temperature,but the elongation and reduction of area increase.When the high temperature tensile temperature of the original sample exceeds300?,the strength decreases and the plasticity increases rapidly.But at 200?,the material still has good mechanical properties,R_m=847MPa,R_0.2=737MPa,A=14%.At this time,it still meets the mechanical properties of 105ksi steel grade drill pipe.After heat treatment,the tensile strength and yield strength of Ti-Al-Mo-V-Zr titanium alloy drill pipe material are about 50MPa higher than the original structure in the temperature range of 25??250?,But after 250?,the strength is almost the same.The analysis shows that when the temperature exceeds 250?,it is equivalent to low-temperature aging treatment of Ti-Al-Mo-V-Zr titanium alloy drill pipe material,the microstructure is more uniform,the content of martensite??is gradually reduced,and the plasticity is improved.At this time,the reduction of area is significantly higher than that of the original unheated structure,and the strength is reduced.