科研之友
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摘要
The composition, morphology, size, and number of inclusions in Fe-22Mn-xAl-0.7C (x = 0.5%, 5.2%, and 10.5%) lightweight steels after smelting and heat treatment experiments are characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy from both 2D and 3D perspectives. The inclusions are classified into eight categories according to chemistry and morphology. For the steel sample with a low Al content (0.5%), the inclusions are MnS, AlN-MnS, and Al2O3-MnS, among which Al2O3-MnS is the primary type. With the increase in Al content in the steel sample (to 5.2%), the populations of AlN and AlN-MnS inclusions of 1-3 mu m in diameter increase. A further increase in Al content (to 10.5%) leads to a significant decrease in the amount of AlN inclusions of 1-3 mu m in diameter, and an increase in the amount of AlN-MnS inclusions. The precipitation behavior during the phase transformation is also studied by FactSage 8.0 thermodynamic software, and a precipitation mechanism is proposed based on the calculation results. During the heat treatment, AlN inclusions re-precipitate out, due to the interactions between Al and dissolved N in the steel matrix. However, AlN inclusions cannot grow large because of unfavorable kinetic conditions. The re-precipitation phenomenon of AlN is predominant under low Al and high N conditions but not at high Al cases.
