Effect of cold rolling on microstructure and mechanical properties of Fe-28Mn-8Al-1C low density steel
The urgent imperative within the automotive industry to realize the strategic objectives of"carbon peak-ing"and"carbon neutrality"has underscored the critical necessity for automobile lightweighting.Based on the merits of low density and excellent mechanical properties,Fe-Mn-Al-C low density steel is considered as one of the candi-date materials for the third-generation automobile steel.Nonetheless,the application process of automobile steel entails a pivotal stage in the form of cold rolling,the ramifications of which on the microstructure and mechanical properties of low-density steel remain unclear.Therefore,cold rolling deformation of Fe-28Mn-8Al-1C austenitic low-density steel with different deformation amounts was carried out.The effect of cold rolling on the microstructure and mechanical properties of Fe-28Mn-8Al-1C austenitic low-density steel was systematically investigated by opti-cal microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray dif-fraction(XRD),electron backscattering diffraction(EBSD),micro-hardness tester,and universal tensile testing machine.The results show that the grains of the tested steel are elongated gradually along the rolling direction from equiaxial shape with the increase of cold rolling deformation,and a large number of slip bands are generated within the grains to coordinate the severe plastic deformation,which eventually form a fibrous tissue at 90%deformation.Dislocation slip is the main mechanism of plastic deformation during cold rolling.Under low strain condition in which the deformation substructure is parallel slip bands,the corresponding deformation texture of the steel which exhibit dislocation slip characteristics is Copper texture.Under high strain condition,the steel exhibits cross slip char-acteristics,the deformation substructure is dislocation wall and dislocation cell,and the Copper texture gradually transforms into Brass texture.The grain size of the steel was refined to 76.5 nm at 90%deformation,because of a sharp increase in dislocation density and a significant enhancement of dislocation interaction induced by deformation.The significantly improved strength and hardness but sharply decreased elongation of the test steel are observed with the increase of deformation,and the tensile strength,yield strength and hardness of the steel reach the maximum at 90%deformation,which are 1 706 MPa,1 653 MPa and 531HV,respectively,while the elongation decreass to 5.3%.The corresponding fracture morphology changes from ductile fracture in the solid solution state to a mixed ductile-brittle fracture after 90%deformation.
low density steelcold rollingmicrostructuremechanical propertytexture
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