The true stress-strain curve for ultra-high strength steel Q&P980 is obtained through cyclic loading of the ultra-high strength steel in terms of the number of cycles, cyclic position and anisotropy of the cyclic tensile test. The properties of the unloading ring were also analyzed to accurately characterize the mechanical properties. A metallographic microscope using X-ray diffraction (XRD) was then used to study the microstructural changes. The results show that increasing the deformation reduced the slope of the unloading and reloading curves. In addition, reducing the austenite content increased the springback strain, elongation and strength, which is called the transformation induced plasticity (TRIP) effect. For similar amounts of deformation, increasing the number of cycles did not increase the springback strain but reduce it when the cycle number increased to 10. The cyclic loading weakens the sheet anisotropy, but has little effect on the elastic modulus and springback.
摘要 为研究超高强钢的循环加载性能, 以淬火配分 (quenching & partitioning, Q&P) 980超高强钢为研究对象, 通过循环次数、循环位置以及各向异性的拉伸实验, 得到真实应力应变曲线, 分析卸载环的性质, 对其力学性能进行准确表征, 再通过金相显微镜、X射线衍射 (X-ray diffraction, XRD) 等检测手段, 分析相应的微观组织变化。发现随着形变程度的增加, 卸载和重新加载斜率不断降低, 回弹应变、延伸率和强度不断增加, 相应的奥氏体含量不断下降, 即具有相变诱导塑性 (transformation induced plasticity, TRIP) 效应。当变形程度相近时, 随着循环次数的增加, 回弹应变不是持续增加, 而是在循环次数增加到10时出现回弹应变减小的情况。循环加载过程会减弱板材的各向异性, 但是对弹性模量和回弹的影响不大。