| 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. |
PDF Full Text Request