Investigation of the aging behavior and orientation relationships in Fe-31.4Mn-11.4Al-0.89C low-density steel

Abstract

The aging behavior and orientation relationships in Fe-31.4Mn-11.4Al-0.89C low-density steel were investigated with respect to constituent phases and precipitates, including gamma-austenite matrix, beta-Mn, and alpha-precipitate. After aging treatment at 550 degrees C for various periods of time, the microstructural changes and corresponding mechanical response were characterized by Vickers hardness measurement combined with EBSD and TEM observations. The precipitation sequence during the aging treatment showed that nano-sized kappa-carbides firstly precipitated within the gamma-austenite matrix at the incipient stage of aging, and induced the primary age hardening. After aging for 300 min, the lath-type beta-Mn phase was formed, leading to the dramatic secondary hardening response. The alpha-precipitates with partial D0(3) order were subsequently produced at the beta-Mn interior, grain/phase boundary region, and the gamma-austenite interior after further aging over 10,000 min. The misorientation-angle distribution, RodrigueseFrank vector space, and orientation relationship stereogram (OR stereogram) from EBSD measurements were employed for analyzing gamma-matrix/beta-Mn and beta-Mn/alpha-precipitate interphase boundaries, respectively. The OR stereograms showed that the preferred orientation relationships were represented as (111)gamma//(221)(beta-Mn), (01 (1) over bar)(gamma)// (01 (2) over bar)(beta-Mn), ((2) over bar 11)(gamma)//((5) over bar 42)(beta-Mn) for gamma-matrix/beta-Mn interface, and (012)(beta-Mn)//(001)(alpha), (02 (1) over bar)(beta-Mn)// (010)(alpha), (100)beta-Mn//(100)alpha for beta-Mn/alpha-precipitate interface, respectively. The orientation relationships obtained from the OR stereograms were clarified by checking the deviation angle distributions of interface segments from the ideal orientation relationships, as well as the TEM diffraction patterns at the interface boundaries. In addition, the misorientation distribution between gamma-matrix and alpha-precipitate was examined and compared to conventional fcc/bcc orientation relationships.