Microstructure and Texture Evolution of X85MnAl29-9 Steel During Aging

The research presented in this paper is part of a larger project concerning high-manganese alloys with different chemical compositions (mainly in manganese content from 21 to 31 wt.%). The presented examination results concern the analysis of the microstructure and textures in high-manganese X85MnAl29-9 steel, an age-hardenable steel, during aging at 550 °C for various times. X85MnAl29-9 steel was first hot rolled and subsequently cold rolled up to a 30% reduction. The samples were aged after deformation at 550 °C for various times in an argon atmosphere and cooled in air. The studies include X-ray phase analysis, texture measurement and observation of the microstructure by light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), as well as microhardness measurement. Research using scanning and transmission electron microscopy identified carbides in the analyzed samples. The results indicate that, when aging takes place, precipitation of κ'-carbide in an austenitic matrix and carbide κ at grain boundaries occurs. The appearance of satellites on diffraction patterns suggests that (Fe, Mn)₃AlC nano-carbides are formed within the austenite matrix by a spinodal decomposition mechanism after the alloy is subjected to long-term aging, which is a key element for structure analysis in the design of safety systems. The use of shorter aging times (up to 24 h) leads to an increase in hardness caused by the precipitation of small κ'-carbide particles in the matrix. However, long aging times (100 h) lead to an increase in the precipitation of the carbide phase (κ and κ'), i.e., the steel becomes overage, which results in a decrease in hardness.