Research On Thermodynamic Calculation And Microstructure-mechanical Properties Of Fe-Mn-Al-C Low Density Steel

In recent years,the study of automotive lightweight materials has become a hot area,because of the use of automotive materials facing environmental protection,resource conservation and other challenges.The development and research of Fe-Mn-Al-C steels with low density and excellent mechanical properties provides a new choice of materials for automotive lightweighting.In this paper,we try to establish the relationship between the composition design,thermodynamics calculation and deformation mechanism of Fe-Mn-Al-C low-density steel.The deformation mechanism is predicted by thermodynamics calculation of the series steel,which provides a basis for the development,design and research of Fe-Mn-Al-C low-density steel.In this paper,thermodynamics calculation results such as phase diagram and stacking fault energy of Fe-Mn-Al-C steel are studied in detail.The phase diagram of low density steels with a range of high aluminum content is calculated by Thermo-calc software.The phase type and precipitation of this steel are studied,and the influences of composition on phase diagram are analyzed too.The results show that the change of aluminum and manganese content in the steel will directly affect the size of each phase area and the precipitation temperature and content of precipitates.On the basis of the Olson-Cohen thermodynamic model,the calculation program was written to obtain the stacking fault energy of Fe-Mn-Al-C steel with different components.The results show that the value of SFE increases with the increase of the content of each element in the steel,and the influence degree of the three is ?SFE+Al> ?SFE+Mn> ?SFE+C,and the basic relationship between stacking fault energy and deformation mechanism is established.The relationship between microstructures and mechanical properties of the two designed steels Fe-28Mn-12Al-1C and Fe-20Mn-10Al-1C are studied in detail too,especially the relationship between the high temperature annealing state.The evolution of hot-rolled,cold-rolled and annealed microstructure of the Fe-28Mn-12Al-1C and Fe-20Mn-10Al-1C steel was studied by means of SEM+XRD+TEM.The room temperature microstructures of 28Mn-12 Al and 20Mn-10 Al steel were coexisted(? + ?),of ot-rolled,old-rolled nd nnealed microstructure of the and steel studied by means he oom temperature of 28Mn-12 Al nd 20Mn-10 Al oexistedand its' density are 6.5025g/cm3 and 6.767 g /cm3,respectively.The microstructures and properties of the steel at different annealing temperatures are different.For example,the microstructures of the 28Mn-12 Al steel annealed at 900? is coexisted in three phases(?+?+?).With the increase of the annealing temperature,the strength of the steel decreases and the plasticity increases,and the product of strength and plasticity is about30-60GPa%,which satisfies the mechanical properties requirements of the third generation AHSS.The deformation behavior of the two steels is closely related to slip bands,and it indicates that the planar glide of deformation bands occupies the main position of the tensile process.In addition,the refinement of the slip bands can also affect the deformation process and the mechanical properties of the steel.