The effect of grain size on stretch-flangeability was investigated to determine its influence on stretch-flangeability of high strength steels. To avoid other effects of microstructure, single-phase twinning-induced plasticity (TWIP) steels were selected for the investigation. To control the grain size of two types of TWIP steels, 1) the initial specimen was annealed at 1100 ℃ to increase its grain size, or 2) subjected to high-pressure torsion then annealed at 650 ℃ to reduce the grain size. The microstructural features were analyzed using the electron backscatter diffraction. The stretch-flangeability of TWIP steels with various grain sizes was evaluated using a hole-expansion test. It was found that the hole-expansion ratio follows the Hall-Petch correlation as does fracture toughness. To improve the stretch-flangeability of high strength steels, microstructural features should be designed to increase their fracture toughness.

研究了晶粒尺寸对拉伸凸缘性的影响，以确定其对高强度钢拉伸凸缘性的影响。为避免微观结构的其他影响，研究选择了单相孪生诱导塑性（TWIP）钢。为了控制两种TWIP钢的晶粒尺寸，1）将初始试样在1100℃退火以增大其晶粒尺寸，或2）进行高压扭转然后在650℃退火以减小晶粒尺寸。使用电子反向散射衍射分析了微观结构特征。使用扩孔试验评估了各种晶粒度的TWIP钢的拉伸凸缘性。已经发现，孔膨胀率与断裂韧性也遵循霍尔-帕奇（Hall-Petch）相关性。