X20CrMoV12.1钢的组织结构和缺口疲劳强度

Microstructures and notch fatigue strength of X20CrMoV12.1 steels

用扫描电镜和透射电镜观察X 20CrMoV12.1耐热钢在545℃长期运行后的微观组织结构变化,研究了不同运行时间后材料的缺口疲劳强度和硬度.结果表明:经过高温长期运行后,X20CrMoV12.1钢的组织明显退化,其显微组织由原来的马氏体板条结构和弥散分布的细小碳化物逐步转变为亚晶粒和分布在晶界上的粗化球形碳化物组织;随着在高温下运行时间的增加,耐热钢的显微硬度和疲劳强度逐渐降低.其原因是基体中固溶体主要合金元素Cr,Mo,V发生贫化,固溶强化效果降低,沿晶界分布的粗化球形碳化物弱化了材料晶界强度,从而导致X20CrMoV12.1耐热钢高温服役寿命下降.

The evolution of microstructures of X20CrMoV12.1 heat-resistant steels exposed at 545 ℃ after long time running was investigated through scanning electron microscope and transmission electron microscope in this study. Notch fatigue strength and hardness of the materials running for different time were also measured. The results show that the microstructures became degraded significantly after long time running. The microstructures were changed from the original martensite lamellar/fine carbides to subgrains/coarsened spherical carbides along boundaries. With increasing running time at high temperature, the microhardness and the notch fatigue strength gradually decreased. The reduction of Cr, Mo and V in matrix results in the loss of solidification strengthening. The coarsened spherical carbides along boundaries reduce grain boundary strength of the material. As a result, the reliability of the X20CrMoV12.1 steels under a long-term service condition at high temperature is degraded.