Effect Of Grain Boundary Design And Control On The Mechanical Behavior Of SUS304

Grain boundary design and control can improve the grain boundary character distribution of materials, make special grain boundary can break network connectivity of large angle boundary effectively, and radically improve the resistance of intergranular failure. It has become an effective means of improving the polycrystalline material performance. So in this dissertation, the widely used SUS304are chosen as model material. Through cold rolling deformation and subsequent high temperature annealing as a method to improve the grain boundary character distribution of materials, we studied the effect of grain boundary characteristic distribution on material’s low cycle fatigue property, room temperature static tensile mechanical property, impact property and high temperature creep property systematically. And we explored the impacting mechanism about special boundary for crack initiation and propagation by fracture Scanning Electron Microscope (SEM) and crack Electron Back-Scattered Diffraction (EBSD). From this work, the following conclusions are drawn:(1) Low cycle fatigue results show that the fatigue life of SUS304is almost twice as long as that of base material under the same plastic strain condition and the transitional fatigue life increased about15times after the optimization of grain boundary character distribution. The secondary hardening strength is greatly improved under the precondition of cyclic softening and hardening behavior not being changed.(2) Tensile results show grain boundary design and control increased yield strength and tensile strength by100MPa and200MPa respectively, elongation reached to72%. Impact results show impact toughness increased by33%after grain boundary design and control. The optimization of grain boundary character distribution enhanced the blocksge of micro crack initiation and propagation.(3) Grain boundary design and control could greatly enhance the high temperature creep properties of304ASS. Under600℃and200MPa condition, matreial’s creep life increased from286h to716h and high temperature elongation boosted from4.35%to6.15%, the average creep strain rate reduced from4.22×10-8s-1to2.38×10-8s-1.(4) By using grain boundary engineering, cold rolling followed by annealing treatment, it not only increased the fraction of special boundaries, but also interrupted random grain boundary connectivity. More low energy special boundaries, especially∑3, prevent crack propagate along the general high angle grain boundaries. So the fracture mechanism of SUS304changed, the crack expand route tend to transgranularly from intergranularly.