Effect of E2₁-Fe₃AlC precipitation on mechanical properties of γ -austenite stabilized by addition of Mn and Co

Effects of Co addition on the phase relation and mechanical properties of an E2₁-Fe₃AlC phase in the Fe-Mn-Al-C system are investigated. The relation between the γ-austenite and E2₁ phases is the same with Co-free alloys. Two kinds of precipitation processes of E2₁ phase from γ-austenite matrix are observed: a fine E2₁ phase precipitation and a cellular structure formation from grain boundaries. The cellular structure formation is explained in relation to the lattice mismatch evaluated by XRD. The lattice mismatch is estimated to be ∼3%, rather higher than that of γ/γ' in Ni-based superalloys, and the volume fraction of the E2₁-Fe₃AlC phase precipitated in the γ-austenite phase is as large as 30%. The micro-vickers hardness increases with increasing Al or C, caused by the increase in the volume fraction of the E2₁-Fe₃AlC phase.