Study On The Microstructure And Properties Of Fe-Mn-Al-C-Cr-Ni Lightweight Steel Modified By TiC/TiB₂ Nanoparticles

With the rapid development of the automotive industry,the pollution caused by exhaust emissions to the environment is becoming increasingly serious.Automobile lightweight is a very important energy-saving and emission reduction measure.The Fe-Mn-Al-C series lightweight steel,as the most promising candidate material for automotive lightweight,has sparked a new research trend.At present,in the study of the mechanical properties of Fe-Mn-Al-C low-density steel,the traditional method of strengthening steel properties often uses the addition of semi coherent intermetallic compounds,carbides,and alloying components,but this will reduce the plasticity and toughness of materials accordingly,which makes it difficult to achieve the balance between strength and toughness of steel.In recent years,increasing the strength and ductility of steel at the same time througth the addition of trace nanoparticles has attracted the attention of scholars.Therefore,the effect of the addition of nanoparticles on the structure and properties of Fe-Mn-Al-C light-weight steel still remains to be explored,and it is worth our in-depth study.In this paper,the effect of trace Ti C/Ti B₂nanoparticles on the casting microstructure and mechanical properties of Fe-Mn-Al-C-Cr-Ni light-weight steel was studied,and the phase precipitation behavior of M₂₃C₆was analyzed.On this basis,the effect of solution treatment on the microstructure and mechanical properties of cast steel was further studied.The hot-rolled Fe-Mn-Al-C-Cr-Ni light steel with Ti C/Ti B₂nanoparticles was used as the research object,it was treated with solution and aging,the influence of process parameters on the precipitation rules of carbides and its properties was discussed.The specific research content and results are as follows:（1）The addition of trace amounts of nanoparticles can significantly inhibit the precipitation of M₂₃C₆carbides at the interface of light-weight cast steel,and can refine the grains,which can increase the tensile strength and elongation of light cast steel by 8.2%and 213%,respectively.The Ti C/Ti B₂nanoparticles increase the content of austenitic phase and reduce the diffusion rate of Cr and C elements through heteromorphic nucleation,thereby inhibiting the nucleation and growth of M₂₃C₆.In addition,the addition of Ti C/Ti B₂nanoparticles increase the number of small-angle grain boundaries and grain boundaries withΣ<9,the lower interfacial energy also inhibited the formation of M₂₃C₆.After the light-weigth cast steel was solution treated at 1000℃,the interphase carbides were completely dissolved.The addition of trace nanoparticles increased the elongation by nearly 1 times after solution treatment..（2）There was no precipitation of carbides in the hot-rolled experimental steel with nanoparticles,the yield strength and tensile strength were 676 MPa and 901 MPa,respectively,and the elongation was 38%.After solid solution treatment,the grain size and ferrite content of the nanoparticle hot-rolled experimental steel increased with the increase of solution temperature.The strength plasticity first increased and then decreased,and the best combination of plasticity and toughness was achieved at 1000℃after solid solution treatment.When subjected to short-term aging at 550℃,no precipitates appeared in the experimental steel structure.With the increase of aging time,the precipitation phase gradually increased,and the precipitation position developed from grain boundary to intracrystalline.After aging for 10 min,the experimental steel still maintained good mechanical properties,with yield strength,tensile strength,and elongation of 484 MPa,754 MPa,and 33%,respectively.After aging treatment at 750℃for different times,the content of precipitated phases in the experimental steel structure increased with the increase of aging time.When the aging time reached 60 min,M₂₃C₆was dispersed in the matrix and the density reached its maximum.Its yield strength and tensile strength were486 MPa and 834 MPa,respectively,and the elongation reached 45%.As the aging time continued to increase,the size of precipitates in the sample further increased,but the density of precipitates decreased.