高锰奥氏体TWIP钢的单向拉伸与拉压循环变形行为

MONOTONIC TENSION AND TENSION-COMPRESSION CYCLIC DEFORMATION BEHAVIORS OF HIGH MANGANESE AUSTENITIC TWIP STEEL

对高锰奥氏体孪晶诱发塑性(TWIP)钢室温单向拉伸与拉压疲劳行为进行了研究.单向拉伸和疲劳实验的应变速率均为6×10-3s-1.疲劳实验采取轴向总应变控制,应变比为-1.结果表明,随拉伸应变的增加,应力-应变曲线上的锯齿状塑性流动呈现出不同的特征,具有很强的应变敏感性.在不同应变幅下的低周疲劳实验中,高锰奥氏体TWIP钢表现出很强的循环硬化能力.低应变幅时表现为初始循环硬化,随后稳定;中等应变幅时,表现为初始循环硬化后出现不同程度的循环软化,然后稳定;高应变幅时经短暂循环硬化后开始循环软化,直至失效.较高应变幅下循环失效后的奥氏体晶粒内产生了大量的位错、位错墙、迷宫结构以及位错胞等位错结构,在部分晶粒内还观察到了细小的形变孪晶.

Twinning-induced plasticity （TWIP） steel, having a great potential in applications in the automotive industry as a new generation of advanced steels, has attracted much attention in recent years because of the excellent combinations of strength and ductility resulting from deformation twinning. The monotonic tension behavior of TWIP steels has been extensively investigated; however, the serration behavior and low-cycle fatigue （LCF） properties have not been well understood. In order to obtain a good understanding of the mechanisms of room temperature serrated flows and the cyclic deformation behavior, the monotonic tensile deformation and fully reversed tension-compression LCF behaviors along with the deformed microstructures of an annealed TWIP steel were investigated in the present work. Both monotonic and fatigue tests were performed at room temperature with a strain rate of 6× 10^-3 s^-1. The fatigue tests were conducted under total strain amplitude control with strain amplitudes ranging from 0.002 to 0.01. The tensile results show that the serrated plastic flows of stress-strain curves, presenting distinct characteristics at various strain levels, exhibit strong strain-level sensitivity. With increasing strain, the type A serrations featured by fine step-like flow are gradually replaced by the largely increased amplitude of type A serrations and their oscillation frequency decreases apparently; however, the frequency of type B serrations increases and the amplitude reduces slightly. The LCF fatigue results show that high cyclic hardening capacity is exhibited at all strain levels. At low strain amplitudes, the steel exhibits a very small initial cyclic hardening followed by a long saturation untill fracture. At medium strain amplitudes, a moderate initial cyclic hardening is followed by different degrees of cyclic softening depending on the applied strain amplitude, and then saturation untill fracture. At high strain amplitudes, the steel shows a rapid cyclic hardening quickly followed by softening till final fracture, almost without a saturation stage. Furthermore, at higher strain amplitudes, cyclic loading is found to lead to the generation of fine deformation twins in addition to high density of dislocation substructures, including dislocation wails and cell-like structures.