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

In this paper, two different high-management high-aluminum steels, Fe-26Mn-6Al-C steel and Fe-26Mn-12Al-C steel, were studied. The microstructures and mechanical properties of the steels at different heat treatment states were investigated. By detailed observing the microstructures at different plastic deformation stages, the deformation mechanism of the experimental steels was analyzed. In addition, by comparing and analyzing the tensile results of the two experimental steels, the strain hardening behaviors were studied. This work may provide important theoretical basis and useful experimental evidences for the future engineering production and application on high-management high-aluminum steels. The main contents and results can be summarized as following:(1) The Gibbs free energy and stacking fault energy of two different Al content high-management high-aluminum steels were calculated. The results indicated that the stacking fault energy of the steels increased with the increase of aluminum content.(2) The microstructures and mechanical properties of Fe-26Mn-6Al-C steel, which was labeled as No.6Al experimental steel, were investigated. The results showed that the microstructure of the hot rolled No.6Al steel was fully austenitic. After solution treatment at different temperatures, the microstructure was still austenite. With increasing the solution treatment temperatures, the strength decreased and the elongation increased. After1100℃solution treated, the yield strength, ultimate tensile strength and elongation were378MPa,756MPa and57%.(3) The microstructures and mechanical properties of Fe-26Mn-12Al-C steel, which was labeled as No.12Al experimental steel, were investigated. The results indicated that the microstructures of the steel were constituted with primary austenitic phase and some ferrite. After solution treatment at different temperatures, the tensile strength decreased and the elongation increased with increasing the treatment temperatures. For the1100℃solution treated steel, the yield strength and elongation were952MPa and37.3%. Moreover, in the microstructure of the steel after1100℃solution treated, a super lattice structure in the austenite matrix was observed by using TEM.(4) The microstructures of the two experimental steels at different deformation stages were observed. For No.6Al steel, both the planar slip and TWIP effect are the main deformation mechanisms. However, for No.12Al steel, only planar slip was observed.(5) The two experimental steels were aged at550℃for different aging time. It was found that the aging strengthening of the two steels is significant. Especially, for the No.6Al steel, the comprehensive mechanical performance has been well improved after10hours aging treatment. The elongation of No.12Al steel after aging treatment should be further enhanced.(6) The TWIP effect was observed in the deformation stage of No.6Al steel with lower stacking fault energy, but not in No.12Al steel. As a result, the strain hardening exponent of No.6Al steel was larger and varied in a wider range than that of No.12Al steel.