Study On Microstructure,Mechanical Properties And Heat Treatment Of Fe-12.6Mn-9Al-0.8C Low Density Cast Steel

Fe-12.6Mn-9Al-0.8C low density steel was fabricated by smelting,ingot casting and heat treating,etc.The low density cast steel with tensile strength higher than 600 MPa,elongation higher than 45%,and weight loss higher than 10 was exploited successfully.The microstructure,mechanical properties,hardness of the low density steel was tested and analyzed by tensile test,impact test,OM,XRD,SEM and fracture scanning,etc.The results are as follows:Fe-12.6Mn-9Al-0.8C low density steel is a stable two-phase structure of austenite and ferrite.The lattice constant of austenite is 3.6643 ?,and the lattice constant of ferrite is 2.8978 ?.The addition of lightweight elements of Al and Mn expands the matrix of the Fe and decreases its density.The solid solution treatment affects the toughness of Fe-12.6Mn-9Al-0.8C low density steel by controlling grain boundary carbide precipitation.After solid solution treatment at 700? and 750?,the grain boundary of austenite and ferrite has continuous ?-carbide precipitation,and the strength and toughness of steel are reduced.Solid solution treatment can transform the morphology of dendrites,reduce the long ferrite phase and increase the strength and plasticity of steel.Nevertheless,too high solid solution temperature or time will result in the ferrite structure to be coarse and the strength and toughness of steel will decrease.After solution treatment at 1000°C,the low density steel showed a good combination of strength and toughness.The tensile strength was 644.16 MPa,and the elongation after was 40.31%.Aging treatment significantly increases the strength of low density steels without significantly reducing plasticity,thus obtaining a better combination of high strength and toughness.The morphology and distribution of carbide in the aging treatment of low density steel and the effect of carbide on the mechanical properties of steel was investigated by XRD and SEM.The results demonstrate that as the time of ageing treatment increases,the size and number of the carbide increase,mainly distributed at grain boundaries.After 5 hours aging treated at 500°C,the low-density steel showed a good combination of toughness and toughness.The tensile strength was 735.53 MPa,and the elongation was 20.1%.The effect of homogenization annealing and normalizing process on the microstructure and properties of low density steel were studied.The results demonstrate that the homogenization annealing can effectively eliminate the dendrite segregation of low density steel,making the structure and composition more uniform,but the phenomenon of grain growth is serious.Normalizing treatment can make the grain of low density steel become fine and the plasticity increases.The tensile strength was 618.49 MPa,and the elongation was 45.13% after normalizing at 850°C.