鐵-35錳-7鋁-4鉻-0.7碳合金相變化

Abstract

The main studies of this paper are to analyze the phase transformation of the Fe-35Mn-7Al-4Cr-0.7C alloy. During the 1050℃/30min. solution heated, the microstructure of the present alloy is a single γ phase with lattice parameter a=0.369 nm. Aged at 450℃ for various times, a γ → (γ+κ+Al6Mn) transition can be found within matrix. The lattice parameter of the Al6Mn belonging to FCC structure is a=0.408nm. It is noted here that the observation of Al6Mn precipitate has not been reported in the Fe-Al-Mn-C alloy system. When aged at 550℃ for various times, a γ → (γ+Cr7C3) → (γ+Cr7C3+β-Mn) transition can be found. No evidence that the ferrite phase and κ-phase carbides could be found. The lattice parameters of Cr7C3 and β-Mn phase are a=1.392 nm, c=0.453 nm and a=0.610 nm, respectively. Increasing the aged temperature to 750℃, some DO3 phase particles with lattice parameter a=0.581 nm are found on the grain boundaries. Prolong the aged time, some Cr23C6 carbides with lattice parameter a=1.054 nm are found. Being heated at 850℃, both of the Cr23C6 and Cr7C3 carbides are observed. Meanwhile, the exist temperatures of the Cr7C3, β-Mn and Cr23C6 are in the range of 550-850℃, 550-750℃ and 750-850℃, respectively. Moreover, the twin of the austenite phase can grow along direction and stable along direction.