Thermodynamic calculation,microstructure and property of Fe-Mn-Al lightweight high-strength steel containing rare earth Ce
In order to acquire the phase composition and microstructure and performance characteristics of the Fe-Mn-Al lightweight high-strength steel containing rare earth Ce,and then improve its comprehensive mechanical prop-erties,the phase composition,microstructure and typical mechanical properties of it are studied by combining thermo-dynamic calculations and experiments and the effect of solution treatment temperature at 900-1 100 ℃ on its micro-structure and properties are analyzed.The results show that the main phases of the tested steel includes ferrite,aus-tenite,κ carbide,Ce2C3 and NbC in the temperature range of 600-1 200 ℃.When the temperature is higher than 865 ℃,the carbides are almost completely dissolved in the matrix and the single-phase austenite region exists be-tween 865-915 ℃.When the temperature exceeds 915 ℃,ferrite begins to precipitate from the austenite.The ferrite content gradually increases with the increase of temperature,and the temperature range of 915-1 200 ℃ is the two-phase region of austenite and ferrite.The austenite content in the hot-forged test steel is about 86.4％,with an aver-age austenite grain size of about 28 μm and a large amount of deformation twinning inside.After solution treatment,the ferrite content increases and the grains begin to coarsen.Most of the ferrite in the banded structure is broken and separated,distributed in small particles along the austenite grain boundaries,and a small amount of annealing twins begin to appear inside the austenite.Besides,the tensile strength of the test steel is significantly reduced,and the plasticity is improved.When the solution temperature is 1 000 ℃,the tensile strength of the tested steel is 889.6 MPa,the elongation at break is 47.1％,and the strength-ductility prod uct reaches a maximum of 42.08 GPa·％.It is for that,on the one hand,the plasticity of the test steel is significantly improved due to the increase of ferrite content,and on the other hand,the two-phase structure of austenite and ferrite is evenly distributed,and the grains are fine,which is conducive to the improvement of strong plasticity.Therefore,compared with that at the solution temperature 900 ℃,the tensile strength of the test steel at 1 000 ℃ did not decrease significantly,while the plasticity increased by nearly double.
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