690合金传热管疲劳裂纹扩展研究

Fatigue Crack Growth of Alloy 690 Tubing

采用销加载拉伸方法和直流电压降法测试技术,测量了室温和高温325℃空气中3种不同工艺的690合金传热管的疲劳裂纹扩展速率.试验采用Paris-Erdogan公式进行拟合分析,证明了结果的真实性和可靠性.高温加速了疲劳裂纹扩展.由疲劳裂纹扩展速率曲线可以预测出3种690管材在高温325℃下的门槛应力强度因子幅值ΔKth,扫描电子显微镜下观察断口形貌,疲劳裂纹的扩展为穿晶形式,在穿晶断口上观察到明显的疲劳辉纹和微塑性区.

Fatigue crack growth rate （FCGR） data of three kinds of alloy 690 by different manufacturing process were generated in air at room temperature and 325 ℃ using the pin-loading tension （PLT） specimen and direct current potential drop （DCPD） method. The testing data were modeled with the Paris-Erdogan equation, and a linear relation between log（da/dt） and log（ΔK） was observed, which indicated good veracity and reliability of results. The threshold stress intensity factor amplitude ΔKth of the three alloys was predicted from the fatigue crack growth curve at 325 ℃, and material B has the highest ΔKth, showing best fatigue resistance performance. Scanning electron microscopy （SEM） examination of the fatigue fracture surfaces revealed transgranular attack, and the transgranular regions of the fatigue fracture surface were covered with striation-like features, indicative of micro-plastic deformantion.