Microstructure and mechanical behavior of a novel Fe–Mn–C–Cr–Si high-manganese steel

The microstructure and mechanical properties of a novel Cr and Si co-alloying Fe–0.6C–15Mn steels, labeled as 2Cr(3Si), 4Cr(3Si), 6Cr(3Si), and 4Cr(0Si), were investigated. All samples for mechanical property test and microstructure analysis were subjected to solution treatment at 1100 °C for 1 h after forging. The results indicate that the microstructure for the 2Cr(3Si), 4Cr(3Si) and 4Cr(0Si) steels mainly consists of the full austenite, and grain size is about 100 μm, whereas the microstructure of the 6Cr(3Si) steel exhibits austenite and some undissolved Cr7C3 carbides. The refined austenite grain size of 48 μm is obtained in 6Cr(3Si) steel. The strength and elongation of the experiment steels with Si and Cr increase significantly with the Cr contents. Among the steels, the 6Cr(3Si) steel has the maximum yield strength, tensile strength and elongation of 490 MPa, 987 MPa and 41.5%, respectively. And the impact toughness is 151 J cm−2. The Si-free steel (4Cr(0Si)) exhibits a low yield strength (372 MPa) and a high tensile strength (992 MPa). The high elongation of 74.8% and impact toughness of 320 J cm−2 are obtained. The results also demonstrate that the Cr and Si co-alloying in high-Mn steels is beneficial to improve work hardening capability, and the work hardening capability increases with the increase of Cr content. According to the results analyzed by the electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), the strain-induced ε-martensite is dominant at the low strain level and the content of ε-martensite increases with the increase of the tensile strain. The maximum amount of the ε-martensite is found in the 6Cr(3Si) steel. With the strain increasing, α'-martensite appears in microstructure, which is formed on the ε-martensite. In addition, the stacking faults (SF) and mechanical twins (MT) are also observed.