Microstructure and Properties of a Low-Density Steel with High Strength of 1350 MPa

A low-density steel Fe-20Mn-10Al-1.0C with high strength of 1350 MPa was developed. The mechanical properties and microstructure evolutions of Fe-20Mn-10Al-1.0C steel under various heat treatment conditions were investigated by means of optical microscopy, X-ray diffraction and high resolution electron microscopy. The results show that the alloy goes through spinodal decomposition leading to the L′12 ordered phase-κ′ carbide (Fe, Mn)3AlCx formation. After solution-treatment at 950 ℃, diffused precipitates of (Fe, Mn)3AlCx with the sizes of 2-5 nm are formed inside the austenite substrate. After the subsequent ageing process, the size of κ′ carbides is increased, and the particles tend to be aligned and agglomerated along the <100> directions with the aging temperature increases. Periodic modulated structures are finally formed into resembling regular "checkered lattice". Ordering effect strengthening by the nano-sized κ′ carbides and elastic misfit strengthening by spinodal decomposition cause a high tensile strength up to 1350 MPa with a good elongation, and the density is lower than 6.80 g/cm3