Microstructure control and ductility improvement of the two-phase γ-Fe/κ-(Fe, Mn)3AlC alloys in the Fe–Mn–Al–C quaternary system

We have conducted a series of investigations to design γ-Fe based heat resistant alloys strengthened by the E21 type intermetallic compound (Fe, Mn)3AlC, κ phase. The γ-Fe/κ-(Fe, Mn)3AlC two-phase microstructures were examined with phase equilibria in the Fe–Mn–Al–C quaternary system. Mechanical properties of as-annealed γ/κ two-phase alloys were evaluated by compression and tensile tests from room temperature to 1073 K. All the alloys show excellent compressive plastic deformability at all test temperatures, however, they exhibit almost zero ductility in tension particularly at ambient temperature. Coarse κ phase or/and thick κ phase film precipitating on γ grain boundaries was found to be one of the causes of this brittleness. Improvement of ambient temperature tensile ductility was attempted by the specific heat treatment to form the γ/κ lamellar microstructure via discontinuous precipitation; to diminish κ precipitates on γ grain boundaries and to soften γ matrix being fully strengthened by fine κ precipitates.