Microstructure And Mechanical Properties Of 0.1C5Mn3Al Warm-drawn Duplex Steel With Laminated Structure

In recent years,in order to achieve the goals of energy saving and environmental protection,researchers have spent more energy and time in the lightweighting of steel materials.Studies have shown that adding moderate amounts of aluminum to medium manganese steel(such as 5Mn3 Al duplex steel)can reasonably reduce the density of the material.Recent researches have shown that laminated 5Mn3 Al duplex steel fabricated by hot rolling have very good elongation,but the strength is slightly low.In this research,0.1C5Mn3 Al duplex steel was used.Higher strain was achieved by warm drawing at 600? in order to refine the layer thickness and to improve the strength of the material without scarification the elongation.Furthermore,86% strain(?3mm)drawn sample was heat treated in the temperature range of 500?-850? and the time range of 5min-10 min to tune the microstructure and the mechanical properties.The mechanical properties of different samples in the drawn state and the annealed state were tested using a universal tensile machine and a hardness tester;the microstructure analysis of the drawn state and the annealed state of the material was carried out using optical microscopy and scanning electron microscopy(SEM).The main results are as follows:(1)The laminated 0.1C5Mn3 Al dual phase steel can be prepared by warm drawing.With the increase of the drawing strain,the strength of the material increases,but the elongation decreases.23% drawing strain can improve the yield strength of the material greatly,from 600 MPa in hot rolled state to 920 MPa.On the other hand,the plasticity of the material decreases rapidly,and its total elongation is even less than5%.(2)With the increase of the drawing strain,the lamellar spacing between the ferrite phase and the martensite phase is gradually refined.When the drawing strain is86%,the layer thickness of the ferrite-martensite layer is reduced from the original6.68?m before drawing to 2.26?m after drawing.(3)The results of heat treatment studies show that with the increase of annealing temperature and the extension of annealing time,the yield strength and tensile strength of the material decrease,and the uniform elongation and total elongation increase.Annealing at 750? for 5 minutes has a better mechanical property where the strength is 861 MPa and the total elongation is 20%.Tts strength exceeds the original hot rolled state,and the elongation is similar.(4)After annealing at 500-550? for 5 minutes,the microstructure maintains the martensite-ferrite dual-phase layered structure,and carbides precipitate in the martensite phase;after annealing at 600-650? for 5 minutes,the original ferrite phase is slightly After recovery,the original martensite phase decomposed into a new ferrite phase and carbonized precipitates;after annealing at 700-750? for 5 minutes,the ferrite grains obviously recovered and recrystallized,and grew thick in the rolling direction After annealing at 800-850? for 5 minutes,equiaxed fine ferrite grains and martensite / austenite island-like structures are formed in the martensite.