| As the third generation automobile steel, Fe-Mn-Al-C steel has the characteristics of low density, high strength and plasticity, good forming property and low cost, also, it can reduce the weight, fuel consumption and improve the safety performance of the car, therefore, it has a very good application prospects. The author designs three kinds of medium manganese steel with different Al content, Fe-10Mn-6Al-0.25 C, Fe-10Mn-8Al-0.25 C, and Fe-10Mn-10Al-0.25 C, which are cast by medium frequency induction furnace in the atmosphere. The study researches effect of experimental steel structure of casting state and mechanical property with different Al content by optical microscopy(OM), XRD, scanning electron microscopy(SEM) and energy spectrum analysis(EDS), electron probe(EPMA), and so on.. It also focuses on the effect of different solid solution treatment temperature, rolling parameter as well as the effect of heat treatment process on the microstructure and mechanical properties of laboratory to explore ways to further improve the mechanical properties of experimental steel.The results show that:The microstructure of test steel which is casting state with different Al content by using the intermediate frequency furnace at room temperature is coarse austenite and ferrite, and austenite is distributed in ferrite matrix, at the same time, there was a carbon enriched phase in the tissue. With the increase of Al content, the volume fraction of austenite of the steel decreases, and dimensional morphology has also changed. The experimental results are as follows:The morphology of the austenite phase of 6%Al steel is the block with poor stability, and the austenite of 8%Al steel is in bar shape, and the size of austenite in 10%Al steel becomes smaller, which is shorter. Along with the increase of Al content in steel, the enrichment of C elements decreases, at the same time, the concentration of Mn and C elements in steel austenite increases. Under the influence of coarse structure, the tensile strength of casting experimental steel is low, and the tensile strength decreases with the increase of Al element, and 8%Al and 10%Al steel are brittle fracture.The experimental steel with different Al content in the casting state is made of solid solution treatment at 900??950??1000? for an hour, which shows that the hardness of 6%Al steel and 8%Al steel is decreased, the strength ductility is improved obviously, and the yield platform of 8%Al steel in the process of the solid solution is obtained.Due to the dominant effect of the diffusion of Al elements, the proportion of ferrite in the three steels after solid solution treatment is increased, the size and morphology of austenite has also changed. 6%Al steel is changed into strip after treatment. The microstructure of 8%Al steel is changed fromrod-shaped to lath-shaped, furthermore, after the solution treatment of 6%Al and 8%Al steel at 900 ? and 950 ?, austenite were brought up on different degrees, besides, after solution treatment at 1000?, the austenite size becomes smaller, which is speculated that the decomposition of austenite occurs. Moreover, with the increase of solid solution temperature, the concentration of carbon in the steel gradually disappears and the transformation of the microstructure and properties in 10%Al steel is not obviousafter solution treatment.8%Al steel of casting state was processed by rolling processing of 40% and 60% two kinds of variable rows, which causes that austenite, ferrite in steel, in addition, with the increase of rolling deformation and under the action of rolling high temperature, austenite size increases, showing a long strip. Test steel after rolling is processed by isothermal quenching at 750? and 800?, which shows that the volume fraction of retained austenite in the test steel first increases and then decreases. |
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