A Review of the Physical and Mechanical Properties of a Cast High Strength and Lightweight Fe-Mn-Al-C Steel

Lightweight, age-hardenable steels in the Fe-Mn-Al-C system are currently being developed as an alternative to quenched and tempered steels. At a composition of Fe-30Mn-9Al- 1Si-0.9C-0.5Mo, all compositions in weight percent, these alloys are almost 15% less dense than traditional steels and are completely austenitic when solution treated above 950° C. Recent research has focused on variations of this base composition and this paper serves as a compilation of the associated mechanical and physical properties of mostly cast materials. In the solution treated condition, lightweight steels have high work hardening rates and excellent ductility with elongations up to 64%. Tensile strength depends on the degree of age-hardening with cast tensile strengths greater than 1,000 MPa and wrought strengths as high as 1,160 MPa. In the aged condition, high strain rate compression tests have recorded yield strengths at 1,334 MPa with work hardening to ultimate strengths of 1,650 MPa. Notch toughness in these steels is mainly a function of the amount of phosphorus, inclusion content, and age-hardening. First principles calculations show that phosphorus substitutes for aluminum in the k-carbide structure and lowers the cleavage energy by 45%. However, with proper steelmaking practice and elimination of phosphorus to levels below 0.006%, this alloy attains Charpy \u27V\u27 notch (CVN) breaking energies of 39 J at -40° C and room temperature dynamic fracture toughness values of up to 420 kJ/m2 in the aged condition. Measured physical properties such as thermal conductivity and thermal expansion were close to those reported for high manganese austenitic steels. The modulus of elasticity was measured in hot rolled plate and found to increase slightly from 156 to 161 MPa with increased aging time