Study on Behavior of Micro crack and Propagation Characteristic of Mild Steels in Corrosive Environment

1.多个初始裂纹萌生，其中工艺区域最发达的一条裂纹为微裂纹。微裂纹沿晶界扩展。在微裂纹扩展过程中，经历了三个阶段。在第一阶段中，工艺区域1裂纹沿晶界以之字形方向扩展，靠近两个工艺区域的根部。微裂纹在新的工艺区域扩展之前停止扩展。通过这种行为可以估计微裂纹扩展速率与应力强度因子之间的关系，发现当K小于其长裂纹下限时，微裂纹扩展速率随应力强度因子的增加而降低。用扫描电子显微镜观察了腐蚀裂纹和大气疲劳裂纹的断口，明确了两种环境下的不同之处。

1. Multiple initial cracks initiate and one of these cracks that has most developed process zone has microcrack. Microcrack propagated along the grain boundary.2. In the behavior of microcrack propagation, there were three steps. In the first step, process zones 1 the crack propagated along the grain boundary in zigzag direction, near the root of two process zones. microcrack stopped propagating until growing of new process zone. Microcrack propagated by the this behavior.It has been able to estimate relationship between microcrack growth rate and stress intensity factor has found to propagate when K is less than its lower limit of long crack that is general consideratic crack growth rate in microcrack decreased in accordance with an increase of stress intensity factor.4. Behavior of crack opening and closure was found to occur even in microcrack.Fractogragrapy of corrosive and atmospheric fatigue crack are permed by scanning electron microsc clear the difference in two types environments.