Effect of Strain Amplitude on Low Cycle Fatigue Properties at Room Temperature of Low Stacking-Fault-Energy Fe-Mn-Si Alloy
Low-cycle fatigue tests at room temperature were carried out on annealed low stacking-fault-energy Fe-29.4Mn-4.3Si-1.4Al-0.049C alloy at low loading strain rate(8×10-3 s-1).The low-cycle fatigue properties and microstructure after fatigue fracture were studied at different strain amplitudes(1％,2％,3％),and the effecting law and action mechanism of strain amplitude on low-cycle fatigue deformation behavior and fatigue life were revealed.The results show that with the increase of strain amplitude,the fatigue life of the test alloy decreased significantly,and the fatigue deformation behavior showed three stages of work hardening characteristics,including initial cycle hardening,cycle saturation and secondary cycle hardening.Increasing the strain amplitude would increase the cycle hardening degree and the rate of increase with the number of cycles,and shorten the initial cycle hardening stage and cycle saturation stage.With the increase of strain amplitude,the average transformation rate of ε martensite in the test alloy increased,the content and size of irreversible massive ε martensite in the microstructure increased after fatigue fracture,and the irregularity degree of strain distribution in the microstructure increased.The fatigue deformation mechanism of the test alloy was plane slip of Shockley partial dislocation and phase transition and reverse phase transition of e martensite.Increasing strain amplitude could increase the mean peak stress of fatigue deformation,promote Shockley partial dislocation separation and formation of massive ε martensite,increase the size of massive ε martensite,and weaken the reversibility of ε martensite transformation and deformation.
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