碳氮共渗层残留奥氏体对疲劳裂纹扩展抗力的影响

Influence of Retained Austenite in Carbonitriding Cases on Resistance to Propagation of Fatigue Crack

采用表面裂纹法研究了残留奥氏体在碳氮共渗层中疲劳裂纹的扩展行为，证实残留奥氏体在疲劳裂纹扩展过程中会形成应变诱发马氏体，从而导致疲劳裂纹扩展速率明显降低．通过裂纹前端塑性区的能量估算，指出上述现象是由于应变诱发马氏体时吸收大量能量的结果．

The investigations in this research aimed to assess the effects of retained austenite in the cases of carbonitriding on the resistance to the propagation of fatigue crack of 20CrMnMo steel by means of the surface-flawed testing method. The results verified that some of the retained austenite in the cases was transformed into strain-induced martensite and as a result, the rate of fatigue crack growth dc/dN diminished remarkably. This transformation, by estimating the energy within the plastic zone in the crack tip, would consume most of the total energy absorbed by the propagation of the crack.