Study On Microstructures And Mechanical Properties Of High-aluminum High-manganese Steels

In this paper, two different high-aluminum high-manganese steels, Fe-26Mn-3Al-C steel and Fe-26Mn-12Al-C steel, were studied. The microstructures and mechanical properties of the experimental steels after different processes of thermal treatment were investigated.By observing the changing TEM microstructures of the experimental steels at different plastic deformation stages, the deformation mechanism was analyzed. In addition, the preliminary study of the strain hardening behavior of the3A1experimental steel was carried out. The work having been done in this paper will provide theoretical and experimental basis for the massive industrial production and application of high-aluminum high-manganese steels in the future. The main contents and results in this paper are as follows:(1) The Gibbs free energy and stacking fault energy of both experimental steels were calculated. The results indicated that the stacking fault energy of the steels increased with the increase of aluminum content.(2) The microstructure of the hot rolled3A1experimental steel was fully austenitic. After solution treatment at different temperatures, the microstructure was still austenitic. With the solution temperature increasing, the grain size and the non-uniform deformation degree increased,while the yield strength, ultimate tensile strength, elongation and strain hardening rate decreased.(3) The microstructure of the12A1experimental steel was constituted with primary austenite and some ferrite. With the solution temperature increasing, the grain size increased,while the volume fraction of ferrite decreased. Moreover, in the microstructure of the12A1experimental steel after solution treated at1100℃, a super lattice structure in the austenitic matrix was observed by using TEM.(4) The microstructures of both experimental steels at different deformation stages were observed by TEM.The results indicated that the deformation mechanisms of3A1experimental steel are planar slip at the early stage of deformation and TWIP effect which occurred later.While,for12A1experimental steel,only slip band was observed.(5) The12A1experimental steel was aged at different temperatures and for different aging time.The experiment indicated that the volume fraction of the second phase increased most obviously with the aging time extending at600℃. When the aging time was extended to13h,most autenitic grains were swallowed by the second phase which became the main component in the matrix.(6) The macro hardness of the12A1experimental steel after different aging process was measured. The reasults indicated that the macro hardness value increased obviously with the aging time extending.This phenomenon is related to the increasing volume fraction of the second phase.