| In this paper, static CCT curve was determined and the results showed that tested steels get all martensite organizations at all cooling rates. The Ac1 and Ac3 temperatures were 667? and 937?.The effects of annealing temperatures on the microstructure and mechanical properties of Fe-0.2C-5Mn-1.5A1 medium manganese steel were investigated on a chamber electric furnace RX-36-10 for 5mm hot-rolled steel sheet at 650 to 720? and for 1.2mm cold-rolled steel sheet at 650 to 750?. The microstructure and components of the steel during annealing were characterized by scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectroscopy. The amount of retained austenite in the steel was determined by X-ray diffraction analysis. The mechanical properties of the steel were investigated by uniaxial tensile testing. Experimental results show that after annealing at 700?, the microstructure of hot-rolled steel sheet is mainly alternating lamellar ferrite and retained austenite, and the amount of retained austenite is about 40%. The elongation and the product of strength and elongation reach their maximum values of 37% and 33115MPa% for the hot-rolled steel annealed at 700? holding for 4 hours, respectively, and the tensile strength is 895 MPa. After annealing at 700?, the microstructure of cold-rolled steel sheet is mainly isometric ferrite and retained austenite islands, and the amount of retained austenite is above 30%. The elongation and the product of strength and elongation reach 31.2% and 27924MPa% for the cold-rolled steel annealed at 700? holding for half hour, respectively, and the tensile strength is 895 MPa.The experiment results showed that austenite stability was affected by the shape of austenite. The austenite in hot-rolled steel was more stable than that in cold-rolled steel as a result of no room temperature deformation before annealing. |
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