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

Abstract

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, Ae1 continuously decreases from 703.7 ℃ (4Mn) to 501.2 ℃ (8Mn), while final temperature of austenite transition (Ae3) linearly decreases from 1005.6 ℃ (4Mn) to 863.0 ℃ (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 (θ)+ the high-temperature ferrite (δ) to the high-temperature ferrite (δ) + martensite (α′) + residual austenite (γ). The residual austenite is distributed in the boundary of δ ferrite and the martensite lath.

Keywords

• medium-manganese steel
• residual austenite
• partitioning
• cementite