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 gamma-Fe based heat resistant alloys strengthened by the E2(1) type intermetallic compound (Fe, Mn)(3)AlC, kappa phase. The gamma-Fe/kappa-(Fe, Mn)(3)AlC two-phase microstructures were examined with phase equilibria in the Fe-Mn-Al-C quaternary system. Mechanical properties of as-annealed gamma/kappa 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 kappa phase or/and thick kappa phase film precipitating on gamma 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 gamma/kappa lamellar microstructure via discontinuous precipitation; to diminish kappa precipitates on gamma grain boundaries and to soften gamma matrix being fully strengthened by fine kappa precipitates. (C) 2004 Elsevier Ltd. All rights reserved.