Study On The Design Basis In The High Specific Strength Of Fe-mn Based Austenitic Steel

Fe-Mn based austenitic steel with high impact energy absorption in the process of plastic deformation, has become a new development direction of steel for automobile. In order to achieve the lightweight and safety requirements, we need to ensure the plastic, reduce the density and increase the strength. Basing on stacking fault energy calculations, groping components by arc melting, a variety of experimental steels are made by induction melting, changing the process of heat treatment, and using the vanadium carbide precipitation to strengthen, to obtain the high specific strength of steel. For studying the law of precipitation in different aging treatment of vanadium carbide particles precipitated in austenite in steel and its influence on performance, using metallographic observation, XRD analysis, scanning electron microscopy and transmission electron microscopy and other characterization techniques.Research shows that there is no obvious strengthening effect with the low content of vanadium, the strengthening effect is obvious when the content improved to 1%.The age hardening is very sensitive to the aging temperature. The precipitation mechanism is observed to differ with different aging temperature. The microstructure shows mainly precipitate in the matrix, and a certain amount of dislocation precipitate by aging at 650℃. Holding at 750℃, the dislocation precipitate gradually dominate and the number of particles that precipitate on the matrix is decreased, also a small amount of stacking fault precipitation, but the precipitation particles dispersed obvious segregation. Aging at high temperature of 800 and ℃850℃, the microstructure shows no matrix point precipitation, but by the dislocation precipitation and stacking fault precipitation coexistence.In the initial deformation, the accumulation speed of the dislocation is to be improved by the precipitation particle, which making a high rate of work hardening. The precipitation particle will decrease the work hardening exponent, leading to reduced cold forming performance. The precipitation particles with different morphology and dispersion will make the uniform deformation capacity of the materials is significantly different.The tensile strength of Fe-30Mn-2.8Al-2.7Si-0.4V-1C alloy reach to 646 MPa,with the highest specific strength, by the addition of light elements Al and Si, density decreases to 7.29 kg/m3,getting the highest specific strength up to113.17 MPa·m3/kg,but the elongation is only 33%. Aging at 550 ℃ for 5 h give the best comprehensive properties, the yield strength increased from 331 MPa to 422 MPa, the elongation still reached 60%.