1. State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan 430081, Hubei, China
Abstract：In order to study the microstructure evolution and work hardening mechanism of an austenitic low-density steel during tensile deformation,SEM,XRD,EBSD and TEM were used to observe and analyze the microstructure of a Fe-30Mn-8Al-0.8C austenitic low-density steel during deformation. The density of the experimental steel was reduced by 12% compared to pure iron upon 8% Al addition. The microstructure of the experimental steel after aging treatment was full austenite with κ-carbide precipitating at grain boundaries. The yield strength,tensile strength and total elongation of the experimental steel at room temperature were 525 MPa,823 MPa and 41.8%,respectively. The product of strength and elongation reached 34.4 GPa·%. The samples were deformed until engineering strains of 2%,10%,and 20% (corresponding to true strains of 0.020,0.095,and 0.182,respectively) and fracture. Dislocations tended to concentrate at grain boundaries and small grains at low strains and presented in large grains at high strains during deformation. With the increase of strain,the grains were refined gradually and the fraction of grain boundaries with low angle increased linearly. The density of dislocations and microhardness increased and twin fraction decreased with strain. The EBSD analyses for the uniformly deformed microstructure and XRD result for the fracture showed that no mechanical twins and deformation induced martensite presented in the deformed microstructure,proving that no TWIP or TRIP effect happened during deformation. Taylor lattice and microband plane dislocation structure were observed at high strain by TEM,indicating a deformation mechanism of microband-induced plasticity for the experimental steel. The evolution of the slip band spacing during tensile deformation was quantitatively analyzed. The flow stress was estimated according to the slip band spacing and formulas. The estimated value was consistent with the tensile test data,indicating that the dynamic slip band refinement was the dominant work hardening mechanism of the experimental steel.
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2023, Vol. 58 
