Research On Annealing Structure And Mechanical Properties Of Fe-Mn-Al-Si Cold Rolled Lightweight Steel

In this paper,six experimental steel with Fe-10Mn-xAl-ySi-0.8C and Fe-15Mn-xAl-ySi-0.8C compositions were investigated.The stacking fault energy?SFE?of six experimental steel was calculated to determine its deformation mechanism.The microstructure and properties of the six cold rolling steel annealed at 900? were investigated.The effect of alloying elements on the microstructure and properties of the annealed steel and the influence of annealing time and annealing temperature on the microstructure and properties were analyzed.The research methods were mainly microscopic observation of the annealed structure by metallographic and SEM;phase analysis and elemental content determination by XRD and EDS;the recrystallization degree,grain size and the orientation relationship analyzed by EBSD;the mechanical properties of the annealing experimental steel measured by room temperature tensile test and the fracture observed by SEM.The research contents and main conclusions of this paper are as follows:?1?The SFE of the experimental steel with six components was calculated.7¹0wt.%Al in the experimental steel leads to the calculation of the SFE more than 60 m J/m²,resulting in the deformation mechanism of the experimental steel being the plane slip of dislocation.The difference of microstructure and properties of cold-rolled experimental steel annealed at 900? and the influence of alloying elements on microstructure and properties were analyzed.It was found that Mn element can improve the austenite stability during annealing,inhibit the precipitation of carbides,and improve the ratio of austenite in the annealed experimental steel.It was also found that the increase of Al element and the decrease of Si element can inhibit the precipitation of the DO₃ phase.When the content of Mn element is 15 wt.%,the content of Al is 8.5wt.%and the content of Si is1.5 wt.%,which is 15Mn-2#experimental steel,there is no carbide and DO₃ phase in the steel annealed at 900?.The tensile strength of the steel can reach 1190 MPa and the product of strength and plasticity reaches 43.7 G Pa·%,which has excellent comprehensive mechanical properties.?2?The effect of annealing time at 900? on the microstructure and properties of the 15Mn-2#steel was investigated.It was found that???transformation occurred during the annealing of 15Mn-2#steel.The amount of???transformation increases with annealing time,increasing the content of solid solution C in austenite phase.It enhances the solid solution strengthening,which leads to the yield strength of experimental steel improving significantly.At the same time,the change of the two-phase orientation relationship during the growth process of?-ferrite leads to more grain slip system of the two-phase tending to be parallel,which improves the ability of dislocation slip between austenite and?-ferrite and leads to an increase of plasticity.?3?Taking 15Mn-2#and 15Mn-3#steel as the research object,the experimental steel was annealed at 840¹000? for 1 min to investigate the effect of annealing temperature on the microstructure and properties.The increase of the annealing temperature can inhibit the precipitation of?-carbide and improve the deformation coordination of ferrite and austenite,improving the plasticity of the experimental steel.The plasticity of the 15Mn-2#steel annealed at 1000? for 1 min can reach 41.7%,the tensile strength reaches 1000 MPa,and the product of strength and plasticity is as high as 42 G Pa*%.The plasticity of the 15Mn-3#steel annealed at 1000? for 1 min reaches 41%,the tensile strength is 1200MPa,and the strong plastic product is as high as 48.4GPa·%,which fulfill the requirements of the third generation of advanced high-strength automotive steel.Therefore,in order to ensure the comprehensive mechanical properties of the experimental steel,the annealing temperature should be selected to avoid precipitation of carbides during annealing.