Study On Deformation Behavior And Physical Model Of Fe-Mn-Al-C Low Density Automobile Steel

High manganese and high aluminum Fe-Mn-Al-C steel owns high strength and ductility,as well as low density.It will reduce weight and fuel consumption,if low density steel would be used by automotive industry.In addition,the strength-ductility balance of Fe-Mn-Al-C steel can resist plastic deformation during impact,which can improve collision performance of vehicle.In order to deepen the understanding of the mechanical properties of the high manganese and aluminum Fe-Mn-Al-C steel,this article established a stress-strain physical model from the point of view of uniform plastic deformation,which suits for austenite ferrite dual phase steel in plastic deformation stage.The concept of statistically stored dislocation and geometrically necessary dislocation were adopted.Fe-18Mn-10Al-0.5C steel was chosen as the experimental object,the evolution of the dislocation substructure was analyzed,according to that,the stress-strain physical model was modified.The main innovative research results are as follows:(1)The Gibbs free energy and the stacking fault energy of the experimental steel were calculated.The results show that the Gibbs free energy equals to 851.06 J/mol,and the stacking fault energy equals to 70.21mJ/m2,which indicates the main plastic deformation mode of the experimental steel is dislocation slip.(2)Different inhomogeneous plastic deformation situations in metals are described,and the stress-strain physical model for inhomogeneous plastic deformation in dual-phase steel was established based on geometrically necessary dislocation density and statistically stored dislocation density:(3)Conducts solid solution treatment to Fe-18Mn-10Al-0.5C experimental steel at different temperatures.With the increase of solid solution temperature,the yield strength and tensile strength decreased,the grain size,austenite phase ratio and elongation rate increased;Conduct tensile test of the experimental steel under different strain rate has been carried out,it was indicated the yield strength and tensile strength of the experimental steel increase with the increase of strain rate,and the elongation increases with the increase of strain rate.In addition to that,the deformation inhomogeneity of the experimental steel increases with the increase of the strain rate.(4)The effect of strain rate on deformation behavior of the experimental steel under different deformation degree were studied:when the strain rate is 10-3s-1,as the plastic deformation increased from 20%to 30%,Taylor lattice and micro band appeared in austenite respectively;when the strain rate achieves 10-1s-1,as the plastic deformation increased from 20%to 30%,the dislocation movements in austenite evolved from dislocation walls into multiple slip.In comparison,the plastic deformation mode of ferrite is independent of strain rate,and dominated by dislocation slip,which has accompanied by severe dislocation entanglement.(5)The effect of strain rate,phase ratio and grain size on the accuracy of the stress-strain physical model of austenite ferrite dual-phase steel was verified.The results show that,when strain rate was 10-1s-1,the calculated results and the experimental data were consistent;when strain rate was 10-4s-1,the effect of dislocation substructure on the mean free path of dislocation motion should be considered;the model can reflect the influence of phase ratio and grain size variation on the hardening behavior of the experimental steel well.