Effect of Mn content on phase transition temperature and microstructure of Al- contained medium manganese steels

Combined with Thermo-Calc thermodynamic calculation, scanning electron microscopy, X-ray diffraction, EPMA, TEM and EBSD technologies, the effects of Mn content on phase transformation temperature and microstructure of the as-cast Fe-xMn-3.4Al-0.34C(x=4-8) experimental steels were investigated. Results show that with the increment of Mn content, A(e1) continuously decreases from 703.7 celcius (4Mn) to 501.2 celcius (8Mn), while final temperature of austenite transition (A(e3)) linearly decreases from 1005.6 celcius (4Mn) to 863.0 celcius (8Mn). With the increase of Mn content, residual austenite gradually increases from undetectable to 12.6%; the microstructure is gradually transformed from the dual-phase microstructure of cementite (& theta;)+ the high-temperature ferrite (& delta;) to the high-temperature ferrite (& delta;) + martensite (& alpha;& PRIME;) + residual austenite (& gamma;). The residual austenite is distributed in the boundary of & delta; ferrite and the martensite lath.