退火温度对TA31钛合金大口径无缝管组织与性能的影响

利用真空自耗电弧炉+电子束冷床炉熔铸了Ti-6Al-3Nb-2Zr-1Mo(TA31)钛合金圆锭,通过铸坯直接斜轧穿孔制备出ø178 mm×12 mm大口径无缝管,研究了不同退火温度(800、850、900、950 ℃)对TA31钛合金组织演变和力学性能的影响。结果表明:轧制态无缝管为变形的魏氏组织,主要由片层状α相集束和原始β相晶界组成;退火处理后,片层状初生α相减少,原始β相晶界消失,组织逐渐均匀化,但当退火温度超过900 ℃后,α相集束粗化并转变为网篮组织;随退火温度的升高,抗拉强度与屈服强度先略微降低后缓慢增大,而伸长率呈先增大后减小趋势,断口形貌由韧性+准解理混合型断裂逐渐变为韧性断裂再转变为韧性+准解理混合型断裂。综合分析认为,短流程制备的TA31钛合金大口径无缝管适宜退火温度为900 ℃左右,此时抗拉强度、屈服强度和伸长率平均值分别为873 MPa、785 MPa和12.8%。

Effect of annealing temperature on microstructure and properties of large-diameter TA31 titanium alloy seamless tube

Ti-6Al-3Nb-2Zr-1Mo(TA31) titanium alloy round ingots were cast by using vacuum consumable electric arc furnace and electron beam cooling bed furnace, and a ø178 mm×12 mm large-diameter seamless tube was obtained by directly cross piercing, then the effect of annealing temperature (800, 850, 900, 950 ℃) on microstructure and properties of the seamless tubes was studied. The results show that the rolled seamless tube in deformed Widmanstätten structure is mainly composed of lamellar α-phase colonies and original β-phase grain boundaries. After annealing, the lamellar primary α-phase reduces and the original β-phase grain boundaries disappear, with the microstructure being gradually homogenized. But when the annealing temperature exceeds 900 ℃, the α-phase colonies are coarsened and transform into a basketweave structure. With the increase of annealing temperature, the tensile strength and yield strength of the tube first decrease slightly and then slowly increase, while the elongation first increases and then decreases, and the morphology of fracture changes from ductile + quasi-cleavage mixed fracture to ductile fracture and then to ductile + quasi-cleavage mixed fracture. The comprehensive analysis shows that the suitable annealing temperature for the TA31 titanium alloy large-diameter seamless tube prepared in a short process is about 900 ℃, at which the average values of tensile strength, yield strength and elongation are 873 MPa, 785 MPa and 12.8%, respectively.