Effect of solid solution temperature on microstructures and mechanical properties of Fe-30Mn-8Al-0.8C low density steel
To study the microstructure evolution and mechanical properties of Fe-30Mn-8Al-0.8C(wt.％)low densi-ty steel treated at different solid solution temperatures varying from 900 ℃ to 1 100 ℃,the growth behavior of aus-tenite grains was analyzed using OM,EBSD and XRD.Sallars model was adopted to fit the austenite grain size after solution treatments with different temperatures and time.The growth model of austenite grains was established.Tensile tester and hardness tester were used to test the mechanical properties of the experimental steel.The rela-tionship between the microstructure and mechanical properties of the experimental steel was analyzed based on the results of tensile tests and hardness measurements.The results show that the microstructure of experimental steel was austenite with undissolved κ-carbides after solid solution treatment at 900 ℃ for 90 min,which became fully aus-tenitic after solid solution treatment at other temperatures.The austenite grain size increased with solid solution temperature.The austenite grain growth behavior was fitted and analyzed to give a model for the relationship among solid solution temperature,holding time and austenite grain size.The elongation,yield strength and tensile strength decreased gradually with increasing solid solution temperature.Due to the presence of incompletely solidified K-car-bides in the 900 ℃ specimens,which led to early fracture of the specimens,the elongation of the specimens solution-treated at 900 ℃ was slightly lower than that of the 950 ℃ specimens.The optimum strength and plasticity combi-nation of the experimental steel was obtained after solution treatment at 950 ℃ for 90 min.The product of strength and elongation reached 44.3 GPa·％.As the solid solution temperature increased,the work-hardening rate de-creased,resulting in a lower work-hardening term for the tensile strength.According to the Hall-Petch relationship,the equation for the relationship between yield strength and grain size of the experimental steel was given.The me-chanical properties of as-solid-solution Fe-30Mn-8Al-0.8C austenitic low-density steels with high-Mn and high-Al concentration can be predicted by considering the growth model of austenite grain.
low density steelsolid solution treatmentaustenitegrain growthmechanical property
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