大口径厚壁管道热挤压成形过程微观组织模拟及实验研究

Simulation and experimental study on microstructure of large diameter and thick wall pipes during hot extrusion forming process

针对某型核能发电用P91大口径厚壁无缝管道进行了不同挤压比条件下的垂直正挤压成形过程缩比数值模拟,研究了管道微观组织在挤压过程中的演变规律。研究表明:挤压过程中金属温度场变化和局部变形速率对管道晶粒组织演变具有重要影响。相同工艺因素条件下,平均晶粒尺寸在轴向上从变形区到挤出端逐渐递增,而在径向上从管道内侧到外侧逐渐递减;管道内侧的动态再结晶百分数高于外侧;管道金属在轴向比径向有更高的动态再结晶发生率,且动态再结晶晶粒尺寸比径向更小。管道的平均晶粒尺寸随着挤压比的增加呈减小的趋势,挤压比越大,动态再结晶发生的越充分,越利于晶粒细化。进行了与数值模拟相配套的缩比挤压成形实验,并针对获得的样件分别进行了金相实验和晶粒度评定,所测得的平均晶粒尺寸变化规律与数值模拟基本吻合,证明了数值模拟的正确性,同时验证了增大挤压比对管道晶粒细化具有重要的促进作用。

The scaling numerical simulations of the vertical forward extrusion process of a certain type of P91 large diameter and thick wall seamless pipe for nuclear energy power generation under different extrusion ratios were carried out to research the microstructure evolvement regularity in the extrusion process.The results show that the change of metal temperature field and local deformation rate in the extrusion process has important effect on the microstructure evolution of extruded pipe.Under the same process factor condition,the average grain size increases gradually from the deformation zone to the extrusion end in axial direction,and decreases gradually from the inner side to the outer side of the pipe in radial direction;the percentage of dynamic recrystallization inside the pipe is higher than that outside the pipe;the dynamic recrystallization rate of pipe material in axial direction is higher than that in radial direction,and the dynamic recrystallization grain size is smaller than that in radial direction;the average grain size of the pipe decreases with the increase of extrusion ratio;the greater the extrusion ratio is,the more sufficient the dynamic recrystallization occurs,the better the grain refinement is.The metallographic experiments and grain size evaluation were carried out for the samples obtained by scaling extrusion experiments matched with numerical simulations,it is indicated that the experimental results about average grain size variation are basically consistent with the numerical simulations,which shows the correctness of numerical simulations and verifies that increasing extrusion ratio plays an important role in promoting grain refinement.