基于加工图的新型钛合金斜轧穿孔温度预测

Piercing temperature prediction via processing map for a new marine titanium alloy

摘要:

采用GLeeble-3500热模拟机对新型海洋用钛合金Ti80进行压缩试验,研究了该合金流动应力在不同变形参数下的变化,并建立了高温本构方程和热加工图。由加工图中优化出的高功率耗散安全区,初步判断斜轧穿孔法制备Ti80合金无缝管坯时的棒料初始温度；并由有限元模拟及物理实验予以验证。结果表明：在同一应变速率下,Ti80合金流动应力对温度的敏感程度不同,在两相区变形,流变应力会随温度的降低而急剧增大；在单相区变形,流动应力则相差不大。建立的应变补偿型Arrhenius双曲正弦函数,经验证能够准确预测流动应力的变化。所绘热加工图明确指出了Ti80合金热塑性成型时两个优化的工艺窗口：一是在两相区低应变速率,即925-975℃/0.01-0.1s_-1附近；二是在单相区中等应变率,即1050-1100℃/0.1-1s_-1附近。进一步对棒料初始温度在950、1050和1100℃条件下的斜轧穿孔过程进行三维热力耦合有限元模拟,发现950℃穿孔时顶头轴向力会激增为单相区穿孔时的5-6倍,从而导致扎卡；而单相区穿孔均能顺利进行。为降低能耗,最终确定棒料初始温度1050℃为最优穿孔温度,并且在狄舍尔斜轧穿孔机上一火次成功试制出Ti80合金无缝管坯。

Abstract:

Isothermal hot compression tests of a new marine titanium alloy Ti80 were conducted on a Gleeble-3500 thermal simulator. The variation of flow stress under different processing parameters was studied and elevated temperature constitutive equation and processing map were established. Based on the analysis of high power dissipation efficiency in safe region, the initial temperature of bar stock was preliminary determined as Ti80 alloy seamless tube was prepared through rotary piercing process. Finally, the judgment was proven by 3D thermo-mechanical coupled simulation as well as physical experiment. The results show that the flow stress of Ti80 alloy varies with sensitivity of the temperature under different strain rate. The stress will increase sharply with decreasing temperature in α+β phase field; while has slight difference in single β phase field. Taking strain compensation into consideration, the modified hyperbolic-sine Arrhenius type equation could give an accurate estimation of flow stress for hot deformation of Ti80 titanium alloy. The developed processing map shows two high power dissipation efficiency domains, one is in α+β phase field with low strain rate, i.e. 925-975℃/0.01-0.1s_-1; the other is in the β regime with intermediate strain rate, i.e. 1050-1100℃/0.1-1s_-1. Finite element simulation for rotary piercing process was further conducted at initial temperature of 950, 1050 and 1100℃ for bar stocks. It is found that the plug force at temperature of 950℃ increases significantly about 4-5 times to that at temperatures in single β phase field, and what is worse, piercing in α+β phase field leads to rolled stock jamming in Diescher mill. However, the piercing process in β phase field can be conducted well. For reducing energy consumption, the temperature of 1050℃ is considered as the optimal choices. In the end, Ti80 alloy seamless tube was produced successfully in Diescher mill.