The Effect Of Alloying Elements On The Low Cycle Fatigue Behavior Of Fe-Mn-Si Alloys

The use of low yield point steel dampers is an important technical means to improve the seismic performance of buildings.However,the fatigue resistance of the currently used(ultra)low-carbon ferritic steels can no longer meet the actual needs.Fe-Mn-Si alloys with low stacking fault energy can have low yield strength and excellent low-cycle fatigue properties,potentially becoming a new type of seismic damping material.Studies have shown that the excellent low-cycle fatigue properties of Fe-Mn-Si alloys are closely related to the (?)martensite transformation and dislocation movement that occur during the tensilecompression cyclic deformation process,which can be adjusted by the alloy composition.This article analyzes the mechanical properties of 6Si,4Si,4Si1.0Al,4Si1.4Al,2.8Ni and Ni Cu alloys.In addition,the microstructure evolution and deformation mechanism of6 Si and 4Si1.4Al during fatigue deformation were studied to reveal the influence of alloying elements on the low-cycle fatigue behavior of Fe-Mn-Si alloys.Studies have found that reducing the Si content and adding Al,Ni and Cu are beneficial to reduce the work hardening rate of the alloy and improve the quasi-static plasticity of the alloy.Moreover,the addition of Al,Ni and Cu makes the alloy exhibit a three-stage hardening behavior during the low-cycle fatigue deformation process and improves the low-cycle fatigue life of the alloy.Further studies have shown that key alloying elements(Si?Al?Ni?Cu)can affect the alloy's microstructure evolution and fatigue deformation mechanism by affecting the stacking fault energy,thereby affecting the alloy's low-cycle fatigue behavior.The deformation mechanism of Fe-Mn-Si alloys in the process of low-cycle fatigue deformation are mainly planar slip of Shockley partials as well as the martensitic transformation and reverse transformation,which determine the evolution of the microstructure during the fatigue deformation process.Plane slip of infinitely dissociated Shockley partials and stress-induced ? martensite transformation are the main deformation mechanisms of 6Si with low SFE,the alloy has poor plastic reversibility,high hardening degree,fatigue life is only 2093 cycles,and the microstructure is mainly thick ? martensite plate.plane slip of finitely dissociated Shockley partials and stress-induced ? martensite transformation are the main deformation mechanisms of 4Si1.4Al with moderate SFE,the alloy has high plastic reversibility and exhibits three-stage hardening behavior(initial cycle hardening,cycle softening,and secondary cycle hardening)during fatigue deformation,fatigue life reaches 7647 cycles.Corresponding to the three different hardening stages,the main features are the proliferation of Shockley partials,the continuous formation of slip bands and the highly reversible martensitic transformation,and the significant increase in the number of martensitic thick plates and cross plates.